Proposed housing complex

TASK 1

1.1 Explain what are thefctors to be considered when selecting at Homagama for this proposed housing complex

Before constructing a building selecting a land is very important.When we selecting a land,most of the factors to be considered according to the usage of the land.The following are some of the main factors to be considered:

1. Safety:

Proximity to high- Voltage power transmission lines.We should check whether there is any high voltage transmission line near to the site.

Presence of toxic and hazardous substances- Before selecting a site we should aware is there any dangerous things stay in that site.

Hazardous air emission and facilities within close proximity Other health hazards Noise

2. Location: We have to see is the place is good for living.mainly we have to

see the lay of land and the water flow.

We should check whether it has any possibility storm. Lay of the land- Try to get the maximum usage of sloping. Water flow- When we select a site we have to control the

water flow in order to avoid erosion.

3. Soil conditions:

Soil type- Check the soil type while doing the site investigation. Soil compaction- According to the soil type decide the

compaction of the site.

4. Topography:

View- We have to decide the plan according to the view of the land.

Position of boundaries.

5. Size and Shape: Check whether the size and shape of the land is suitable for

our plan.

6. Accessibility:

Public infrastructure- We have to think is the place approachable by visitors.

Road- Find is the land close to the main road and can we bring the construction materials easily.

7. Utilities:

Water supply and pressure Sewer collections system Electricity supply

All these services can be given when the land is in a town area or famous side.So it will be better if the land is situated in one of these areas.

8. Cost:

We have to decide is the land valuable for the particular cost.

9. Availability: Find whether the necessary things are available in the

surrounding of the site.The availability and quality of local labors.

10.Public acceptance: We have to ask the neighbours permission for the new

building construction.

11.Drainage: Find out how can we connect and put out the waste water

drainage.Muncipal authorities,terms and conditions related to the building.

12.Local government regulation: Land should be registered under the local government

regulations.

13.State regulations: The land should be situated according to the state regulations.

14.Business value: It is considered mainly for the financial purpose of the building.

1.2 Explain the purpose of site investigation and describe briefly why it is necessary at the initial stage of the project.

We should know the purpose of this investigation before start any construction projects.there are 2 types of site investigation:

1) Surface investigation- This is related with location of the land and surrounding area.(check the design materials)

2) Sub surface investigation- Water table level and soil condition of the land,geological map and previous history of the land.

In construction the design of a structure should be:

Economical Safe to construct Durable Has low maintenance

Achieving of these will depend upon an adequate understanding of the nature of the ground. An adequate and properly structured site investigation is therefore an essential part of construction.

1. Site investigation is a process of site exploration consisting of Boring, Sampling and Testing. The following are the purpose of site investigation. Suitability:

To check whether the site and surrounding are suitable for the project mainly soil condition, land size, shape and location.

2. Design: Obtain all the design parameters necessary for the work.By

this we can decide whether the land is good for our own.

3. Construction: Are there any potential ground or ground water conditions

that would affect the construction.In this matter we should think about the water table level.

4. Materials: Are there any materials available on site? What quantity and

quality? If there not any materials how can we bring it to the site?

5. Effect of changes: How will the design affect adjacent properties and the ground

water? In future is there any disturbance like wind, storm to the building?

6. Identify alternatives:Before start the construction we should clearly know is this the

best location to built this home?

Why is the site investigation necessary at the initial stage of the project?

When select a land, site investigation is very important. Without site investing we can’t build a good construction .If we start the construction without consider about the above factors we will have to face most problems.Some time we can’t do the construction according to the plan.It means the land is not suitable for our construction plan.Even we did the construction,it won’t have stability because of the bad condition of the soil and the affects of the changes.There is a possibility to can’t transver the construction materials to the site.To avoid these matters we should consider about the suitability,design,construction,materials,effect of changes and identify alternatives.

1.3 List out the necessary investigations to be carried out by the consultant B.

If the sub soil investigation is not carried out for construction of two storey building on filled land, assess how it affects the construction affects the constructions affects once it’s started.

The basic steps to be carried out b the consultant B.

Desk study Site reconnaissance Exploratory investigation Laboratory testing Report

Desk study:

The work involves researching the site to gain as much as possible geological data.

Topographic maps, survey maps,geological maps,arial maps etc should be examined.

Therefore consultant B has to research the site and check the topographic servey,geological mps and arial photographs as desk study.

Site reconnaissance: it is divided into 3 types

I. Site inspectionII. Arial reconnaissance

III. Geophysical methods

Site inspection:

This means going over the site and surrounding areas and get an idea about structure and texture of soil,cross-section of formation,ground water condition.For the site inspection consultant B has to go over the site and look for hydrology,slope instability,mining access to site etc.

Arial reconnaissance: Main features like general topography,drainage erosion,soil patterns and

texture can be examined closely from the air and finishes more details within a short time.for the arial reconnaissance consultant B has to take some photographs in air for subsequent detailed study.

Geophysical methods: These methods are used to locate the boundaries between different strata

of soil.They need supplementation by other methods.but it doesn’t produce the properties of strata.

Exploratory investigations: This is mainly done for get accurate and sufficient information of the soil

condition.Therefore consultant B has to take some informations like type of soil,depth and thickness of soil in each stratum,location ofwater table,strength and compressibility of strata.To obtain details of soil he can use 2 types of samples.there are:

I. Disturbed samples- In which the natural structure of soil gets partly or fully modified and destroyed although with suitable precautions the natural water content may be preserved.

II. Undisturbed samples: In which the natural structure and properties remain preserved.

For this sample collection consultant B can use 2 methods

1) Open trial pits

2) Boring

Open trial pits:

• Pits are excavated at the site exposing the sub soil surface thoroughly

• Soil samples are collected various levels

• Soil strata can be inspected in their natural conditions and samples can be obtained conveniently

• Can be used only for shallow depths

This is the chiepest method of exploration to shallow depths.Pits are dug at the exposing the sub soil surface thoroughly.

Boring:Commonly used borings are as followings

Auger boring Wash boring Hollow stem auger boring Percussion boring Rotary boring

Laboratory testing: When the consultant B finished the exploratory investigation,he has to send the

soil for the laboratory test.

Report: After the laboratory testing consultant B has to submit the report of the site investigation.

If the sub soil investigation is not been carried out,how it affects the construction once it started

If the sub soil investigation is not been carried out for construction of two storey building on filled land, we cannot determine the nature of the sub soil and we cannot get details of the seasonal volume changes in the soil,possibility of the ground movement.We can’t predict the likely behavior of the subsoil under seasonal and ground water level changes.By this we unable to find out the bearing capacity of the soil.If we build the construction without knowing the bearing capacity there is a possibility to lack the stability of the building.

1.4 Give the boring method for the sub soil investigation.

Select and justify the applicable method for this housing project.

When, the depth of exploration is large, borings are used for exploration. A vertical bore hole is

drilled in the ground to get the information about the sub-soil strata. Samples are taken from the

bore hole and tested in a laboratory..

Depending upon the type of soil and the purpose of boring, the following methods are used for

drilling the holes.

Auger boring: There are two types of auger,

1) Hand auger2) Machine driven boring

Hand auger boring: An auger has a cutting end which advances the device through the

sub surface as it is turned.

light weight inexpensive equipmenteasy to carry to field sidedisturbed samples taken limited depth

Machine driven Auger :Those are mechanically operates augers.

No extra effort during drilling processDisturbed samples takenCan be used for great depth

Wash boring : A casing tube will be driven to the ground and water forced under

pressure,Water jet will dislocates the material and forms a slurry which is sucked up to the surface,The slurry sucked out from different depths will be collected for examination.

Hollow stem auger boring : Auger will be driven to the ground until the sampling

depth is attained, A center rod inside the hollow pipe rotates with the auger during drilling,After a sample interval is reached, the center rod can be removed and a sampling tool can be introduced within the hollow stem of the auger, which stays inside the borehole to prevent walls from collapsing.

Percussion boring : Heavy chisel or bit dropped repeatedly on the ground, water is added to

the hole during boring,Pulverized material past is brought t the surface for necessary examinations.

Rotary Drilling:

A method of making hole that relies on continuous circular motion of the

bit to break rock at the bottom of the hole. This method, made popular after the

discovery of the East Texas Field by "Dad" Joiner in 1930, is much more efficient

than the alternative, cable tool drilling. Rotary drilling is a nearly continuous

process, because cuttings are removed as drilling fluids circulate through the bit

and up the wellbore to the surface. Cable tool operations are discontinuous and

cuttings removal is inefficient. This difference in efficiency becomes particularly

significant as hole depth increases

Applicable method for this housing plan

According to this sub soil investigation

top soil layer 200mm

filled soil layer water table 3.5m

sandy gravel layer 2.5m

clay gravel layer 3m

wash boring method is good for this housing project.Acasing tube will be driven to the

ground and water forced under the pressure.here the clay gravel layer is higher than the

sandy gravel layer.compaction also wasn’t done satisfactorily.therefore wash boring method

is easy to collect the sample.

1.5 Classify the soil for the purpose of building construction.

Soil:

Soil consists of grains with water and air in the voids between grains.The water and air

contents are readily changed by changes in conditions and locations.Soil can be perfectly dry or

be fully saturated or be partly saturated.Engineers are primarily interested in a soil’s mechanical

properties: strength, stiffness, permeability. These depend on the nature of the soil gains, the

current stress, the water content and unit weight. Soil is a natural material not manufactured

products. Soil is a particulate material and very necessary material; it is not a continuous mass.

The size distribution of soil particles are established by means of sieving and

sedimentation.However, many soils are formed a combination of particles from the main soil

groups and this classification can be illustrated using a triangle called soil classification

triangle.Mainly soil was divided as follows:

1. Cohesive soil:

cohesive soil is composed of extremely small mineral grains shaped like

plates. Water is attracted between the plates by electrostatic forces to varying

degrees based on the chemical composition of the clay. When dry, clay is hard and

rigid due to the close attraction between the grains. When clay is very wet, it

exhibits an almost soupy consistency. these include clays where the fine grained

particles are closely integrated and stick together

2.Cohesion less soil:

Cohesion less soil is composed of larger.

Cohesive Clay

Cohesion less Silt, sand, gravel

Bedrock classification

Igneous Granite, basalt

Metamorphic Gneiss, schist, slate, marble

Sedimentary: Shale (claystone), siltstone, sandstone, conglomerate,

limestone, glauconite, lignite

Soil classification:

• Clay • Silt

• Sand

• Gravel

• Cobble boulder

Clay:

Several different chemical weathering processes from clay minerals.[ Ex.

Orthoclase - ] Three most common clays are Kaolinite, Montmorillonite and

Elite. Clay is microscopic particle and it is less than 0.002 . These are called inorganic

soil and not compressible. They always have variety of particle size mixed together. More liquid/water and no air.Normaly clay particles are <0.002mm in size. This is a very heavy soil and it holds moisture for long periods of time when wet. This soil will retains nutrients and is very fertile but is heavy, sticky and very hard to dig and the last to warm up in the sun.

Silt:

This soil retains moisture and feels slippery when wet. This soil will retains nutrients better than sand but dose not dry out as quickly. Shape of the silt may be sub rounded, rounded and well rounded

Silt Size

Coarse Silt 0.02-0.06

Medium Silt 0.006-0.02

Fine Silt 0.002-0.006

Sand:

This soil tends to be very light and dries out swiftly. Water drains very quickly and makes the soil easy to dig. It is the first to warm in the sun. Sand is fine aggregate, shape of the sand may be sub rounded, rounded and well rounded. Sand is deeply used in construction Engineering

Sand Size

Coarse Sand 0.6-2mm

Medium Sand 0.2-0.6mm

Fine Sand 0.06-0.2mm

.

Gravel:

Gravel is normally the result of physical and mild chemical weathering process. Shape of gravel may be very angular, sub angular, sub rounded, well rounded. Where natural gravel deposits are insufficient for human purposes. This is often produced by quarrying and crushing hard-wearing rocks, such as sandstone, limestone, or basalt. Quarries where gravel is extracted are known as gravel pits.

Gravel Size

Coarse Gravel 20-60

Medium Gravel 6-20

Fine Gravel 2-6

.

.

Boulders:

These are very course soils which >200mm in size.

Bearing capacity of the soil

In Construction Engineering, bearing capacity of the soil determines the type of foundation and number of floors in the building.The safest load per unit area of the ground can carry is called bearing capacity.Bearing Capacity depends upon:

• Compressibility of the soil.

• Structure of soil layers.

• Position of the water table level.

• Quality of the soil

Bearing capacity of soil

Soil TypeBearing Capacity

Rock 600 – 10,000

Hard well compacted gravel 300

Hard late rite soil 200

Good late rite 150

Sandy soil with low water table 150

Sandy soil with high water table 100

Clayey soils 50 – 75

characteristics of silt & clay

Characteristics Silt Clay

Dilatancy (reaction to

shaking), movement of

water in voids

Rapid reaction. Water appears on

surface when shaken. Squeezing

soil causes water to disappear.

Sluggish and no reaction. No

water appears on surface when

shaken.

Dry strength

(cohesiveness in dry state)

Low to medium reaction. Powder

easily rubs off surface of sample.

Slakes readily in water.

High to very high reaction.

Powder does not rub off surface.

Variable slake rate.

Toughness (plasticity in

moist state)

Plastic thread has little strength.

Crumbles easily as it dries. Dries

quickly.

Plastic thread has good strength.

Dries slowly.

Dispersion (settlement in

water)

Settles out of suspension in 15 to

60 minutes.

Settles in several hours or days

unless flocculation occurs.

Visual inspection and feel Some grains barely visible. Feels

slightly gritty when rubbed

between fingers. Dries quickly

and dusts off easily.

No individual grains observed.

Smooth greasy feel when rubbed

between fingers.

Dried coat Easily crumbled in hands. Will not crumble in hands. Dry

lumps can be broken but not

powdered.

Bite test Gritty feeling between teeth. No gritty feeling between teeth.

TASK 2

II.1 List out the type of foundations used in buildings.

Generaly any structure is considered to have 2 parts.Those are

1.sub structure

2.super structure

Foundation is the sub structure which transmits the load of super structure to the underlying soil.All foundations consists of 3 essential parts.

1.foundation bed:which consists of the soil or rock upon which the building or structure rests.

2.footing:it’s normally widened and rests on the foundation bed.

3.fondation wall: which rises from the foundation to a location somewhere above the ground.

Foundation can be broadly classified into 2 types.

1. Shallow foundations.Deep foundations

Strip footing Pile footing Combined footing Mat or raft foundation Plain slab rafts Plain slab stiffened edge Slab & beam raft foundation Down – stand beam raft foundation

Up-stand beam raft foundation

Cellular raft foundation

Deep foundation

Caisson foundations

Pile foundations by method of installation

Displacement piles

Replacement piles

By method of load transmission

End bearing piles

Frition piles

Concrete piles

Precast concrete piles

Cast in-situ piles

Other types of piles

Sheet piles

Fender piles

Anchor piled

Batter piles

Spread footing foundation-

In this, the base of the member transmitting load to the soil is made wider so that load of the

structure is distributed on sufficient area of the soil in such a way that

the safe bearing capacity of the soil not exceeded.

II.2 A

2.1 D by considering the given borehole data, assess the foundation type

for the above housing block. Student can use the appropriate data for

any calculations if necessary.

By considering the given borehole data raft foundation is suitable for the

above housing borehole data. Because the soil at the site is soft and

marshy having uncertain behaviour (sand gravel layer 2.5m, clay gravel

layer 3m)raft foundation eliminates the possibility of differential

settlement. The above housing block is constructed with basement area

for parking facility. Raft foundation distribute of load on entire area as

uniform. This foundation is used to distribute heavy column and wall

loads across the entire building area. To lower the contact pressure

compare to conventional spread footing. It can be used as a bottom of

basement , and candle severed meters

3.2 Functions of a Founda tion

The functions of a foundation are as follows;

To sustain, distribute and safely transfer the total load (dead load, imposed load and wind load) to the

suitable subsoil.

To prevent excessive and differential settlement of the structure.

To provide stability to the structure against many disturbing forces such as wind, rain earthquake, Tsunami

etc.

To provide a level surface for building operations.

To take the structure deep into the ground and thus increase its stability, preventing overturning

3.3 Types of Foundation

Foundations are mainly categorized as two groups as follows;

1. Shallow foundation: Those transfer the loads to the subsoil at a point near to the ground level.

2. Deep foundation: Those transfer the loads to the subsoil some distance below the ground level such as Pile.

There are two type of foundation used in the building process

2. .

Identify and discuss various factors considered in selecting a suitable foundation

Introduction When selecting a building ground for foundation the type of soil must be taken into consideration. The soil have to be tested on the type of foundation is decide according to the bearing capacity of the soil. Lighter structural concepts now enable slimmer foundation to be designed that carry these loads safely.

Foundation is depending mainly on following things.

*The total loads of the building

a. Roof load on the wall.b. Floor load on the wall.c. Wall load on the foundation.

*The nature and bearing capacity of the sub soil

a. Trial holes and subsequent investigationb. Borehole and cone analysisc. Local knowledge

According to the site:-

There have already been many fourteen storied story building finish this reweals that the soil is favorable for constructing many story buildings as it has heavy bearing capacity. So according to local knowledge, almost the bearing capacity of the soil is good.

Borehole: - 0.3-3.0 there is very fine clayey sand is available. So clay is the most difficult of all subsoil with to deal.

There are mostly used three types of foundation available.

In these three according to the borehole Raft foundation was suitable for the construction

Foundation The stability of any structure depends on the suitability of the foundation to take up the load transmitted to it from the superstructure. Foundation is a lowest part of the structure.Which transmits Wight of the structure, together with the effect of live load and pressure, to the material on which the structure resist in

such a manner that the underling material is not stressed beyond its safe bearing capacity. The material of superstructure may be steel, cement, stone or brick, can withstand comparatively higher stress than the earth strata to which the foundations transmit the load. It is therefore necessary to provide a much larger area at the base of foundation. The loads coming on the foundation are broadly classified into the following three types namely.

1) Self weight of the foundation2) Dead load of superstructure3) Live load of superstructure

Types of foundationThe type of foundation chosen will depend on two distinct variables, the total building load, i.e., the weight of the house, and the type and quality of the subsoil. In addition, different weather conditions and soil types may reduce the effectiveness of foundation, depending on the type of soil. The reverse problem is drought, which causes shrinking of the land and is most common in clay soils. Both conditions can seriously affect the self build foundations, causing disturbance and, in extreme cases, cracking of the self build foundations. They are, however, easily avoided if we dig deep enough.

1) Shallow Foundation.2) Deep Foundation.

Foundation is the lowest part of the structure which provides the base for the super structure. This term includes the

portion of the structure below the ground level as well as the artificial arrangement of concrete block, piles raft grillage

etc. provided to transmit the loads on the structure including the dead weight of the structure it self to the soil below.

Purpose of the foundation:

The foundation is provided for main four reasons mentioned below

1. Distribute the forces of super structure and other elements including the self weight over a large area.

2. To load the sub stratum evenly and thus prevent unequal settlement.

3. To provide a level surface for building operation

4. To increase the stability and preventing overturning

Major parts of a foundation

These footings and foundations are influence by

Load bearing capacity of the soil.

Weight of the structure to be erected on the land.

Foundation is classified under two categories they are

Shallow foundation

Deep foundation

3.2.1 Shallow foundation Most sallow foundations are simple concrete footings such as wall footing and column footing. Shallow

foundations are those that bear at a depth of bearing/ Base width equal to less than five. When designing shallow foundation when any of the factors, excavations, soil stabilization, expensive soils are present for a particular site.

There are three types of shallow foundations available;

FOUNDATION

FOUNDATION BED FOOTING FOUNDATION WALL

1.SHALLOW FOUNDATION:- The main objective of shallow foundation is to distribute the structural loads over a wide horizontal area at shallow depth below the ground level. The different three types of foundations which can be included under shallow foundation these are:

Pad foundations Strip foundations Mat or Raft foundations

Shallow foundation-

The object of this kind of foundations is to distribute the structural load to over considerable area of foundation bed.

There are several types of shallow foundation:

Strip footing

Pad Footing

Combined footings Foundations can be broadly classified into two types

1. Shallow foundations

2. Deep foundations

1. Shallow foundation When the foundations place immediately beneath the lowest part of the super structure, it is

termed as shallow foundation. This object to distribute the structural loads over a wider

horizontal area at shallow depth below the ground level.

Shallow foundations are those founded near to the finished ground surface, generally where

the founding depth is less than the width of the footing and less than 3m. These are not strict

rules, but merely guidelines. Basically, if surface loading or other surface conditions will affect

the bearing capacity of a foundation it is 'shallow'. Shallow foundations include pads strip

footings and rafts. Shallows foundations are used when surface soils are sufficiently strong and

stiff to support the imposed loads; they are generally unsuitable in weak or highly compressible

soils, such as poorly-compacted fill, peat and alluvial deposits, etc.

The various types of foundation which can be included under the shallow foundation.

Pad foundation

Strip foundation

Raft or Mat foundation

Foundations are generally classified in two categories those are

Shallow foundation

Deep foundation

Shallow foundations: (sometimes called 'spread footings') include pads ('isolated footings'), strip footings and rafts. Deep foundations: includes piles, pile walls, diaphragm walls and caissons.

Shallow foundations

Pad foundation Strip foundation Raft foundation

Types of foundation

In building construction field, the foundations are act a main role. According to Some qualities of the

foundations, it can be dividing for different types. Those are following.

SHALLOW FOUNDATION

A shallow foundation is one whose width is greater than its depth. They are located just below the

lowest part of the wall or column which they support. Footings are the structural members of shallow

foundation, which are made of brick work, rubble masonry or concrete, those are used to transmit the loads of

the wall or column such that the load is distributed over a large area.

SHALLOW FOUNDATION

A shallow foundation is one whose width is greater than its depth. They are located just below the lowest par of the wall or column which they support. Footings are the structural members of shallow foundation, which are made of brick work, rubble masonry or concrete, those are used to transmit the loads of the wall or column such that the load is distributed over a large area.

There are three types of shallow foundation. They are,

3.3.1 Strip Foundation

This is simple type of foundation used in low to medium rise buildings.

These are used to support and transmit the loads from heavy walls (or load bearing walls).

These can be made out of Random rubble or Mass/Reinforced concrete. It will depend upon the bearing

capacity of the soil and other structural design.

Strip Foundation

(Sources: http://nzdl.sadl.uleth.ca/gsdl/collect/cdl/archives/HASH5149/5f314e8d.dir/p137.gif

Analysis

Strip foundation is used for single storey building. This foundation excavation method is easy and less cost. But in visited

site construction is 6 storey accommodation building. So in visited site this foundation is not suitable.

Strip foundation

This type of foundation is most suitable for light loading structures such as low to medium rise dowelling.(Figure:03)

(Figure:03)

STRIP FOUNDATION

Strip foundations consist of a continuous strip, usually concrete formed centrally under load bearing

walls. The continuous strip serves as a level base on which the wall is built and is of such width as is necessary

to spread the load on the foundations to an area of sub soil capable of supporting the load without undue

compaction. We are using strip foundation for light load structures. It is provided for a load-bearing wall

and also provided for a row of columns which closely spaced that their pad foundations over lap or nearly touch

each other.

Materials

Mass concrete / Rubbles

Type excavation needed

Trench

Number of stories can be construct

Single or two storey

Structural type of the element

Bar / rod element

Strip Foundation

.

Figure 2

Figure 1

Figure 3

Figure 4

Strip footing

Strip footing foundation consists of a continuous strip, under walls. Generally this

Strip consists of a concrete footing which is normally widened and rests on the

Foundation bed, and the foundation wall, which rises from the foundation to a

Location somewhere above the ground. This foundation wall may be constructed

Either by using rubble or brick.

Strip foundation

Strip foundations are used to support a line of loads, either due to a load-bearing wall, or if a

line of columns need supporting. Even where it possible to have individual bases. It is often

simpler and more economic to excavate and construct the form work for a continuous base.

Figure 13_Strip foundation

Figure 14_Strip foundation

Stripe foundation

Strip foundations consist of a continuous strip, usually of concrete formed centrally under load bearing walls. The spread of the strip depends on foundation loads and the bearing capacity and shear strength of the subsoil. The thickness of the foundation depends on the strength of the foundation material. The two types of strip are commonly used.

Wide stripe foundation Deep stripe foundation

Deep strip foundation

The deep strip foundation used to reduce the quality of excavation, backfill and removal of excessive soil. Also it is provide greater resistance to the settlement. Here the depth of foundation is more than 900mm.

Wide strip foundation:

The wide strip foundation will be used when the load bearing capacity of the ground is very low. This foundation type may be used to carry load-bearing walls.

Fig No-05 Strip foundation

Discussion

This foundation is mainly used for one or two storey building. This foundation excavation method is cheap and simple. But our selected site construction is 7 storey building. So that this foundation is not suitable.

3.3.2 PAD Foundation

(Sources: http://www.nottingham.ac.uk/sbe/projects/yr1_CD1_diaries/craig_CD1/Sourceimages/groundworks/

padfoundation_txu.JPG)

Analysis

Pad foundation is usually used for single storey and two storey buildings. Bearing capacity is good visited site put pad

foundation for 4 or 5 storey building. In visited site bearing capacity is not enough to put 6 storey building. So this

foundation also not suitable for this site.

Pad foundation

This type of foundations depends on the load on the foundations and the bearing and shear strength of foundation materials. It is sometimes economical to construct a foundation of isolated piers or columns of brick or concrete supporting reinforced concrete ground beams, in turn supporting walls, rather than excavating deep trenches and raising walls off strip foundations, some depth below ground

Fig No-06 Pad foundation

Discussion

pad foundation is usually used for single storey or double storey buildings. if Bearing capacity is good, we can put pad foundation for 2 - 4 storey building. bearing capacity is not sufficient to put 7storey building. our selected site. So pad foundation also not suitable for this site

Pad Foundation

Pad foundation is isolated slab foundation which support and transmit the load from column

. In general,pad foundation are in rectangular shape and consist of a slab of

uniform thickness.

This type foundation is used for subsoil except loose sand, loose gravel and filled areas.This is divided by two types

1. Isolated foundation

Reinforced concreatbase

Centrally placed reinforced concreate column

50 to75mm thick blinding layer of ash, coarse sand or a lean mix concreat

ISOLATED PAD

o o o o o o o o o o

cloumns or piers placed so that their center of gravity coincides with that of the base

reinforced concretebase

COMBIEND PADblinding

75 mm cover

75 mm cover

50 to 75 mm thick blinding layer of weak concrete toprovide accurate starting level

2. Combined foundation (Figure:02)

(Figure:01)

(Figure:02)

Pad/Isolated Foundation

This type of foundation is used to support and transmit the loads from piers and columns. The most economic plan shape is a square but if the columns are close to the site boundary it may be necessary to use a rectangular plan shape of equivalent area. The reaction of the foundation to the load and ground pressures is to cup, similar to a saucer, and therefore main steel is required in both directions. The depth of the base will be governed by the anticipated moments and shear forces, the calculations involved being beyond the scope of this volume.

This is usually constructed of reinforced concrete and where possible are square in plan. These are isolated slab foundations, which support columns. The most economical form of construction is to provide each column with its own base, the column being set centrally on that base. The thickness of the slab should be equal to the projection of the slab from the side of the column.

Typical Pad Foundation Types

Material

Reinforced concrete

Type of excavation needed

Pits

Number of stories can be construct

Three to four stories

Structural type of the element

solid

Combined column foundations - Outer column close to boundary or existing wall

Isolated or pad foundation – Design to span in two directions therefore main bars are placed in the bottom both ways.

Steel grillage foundation - Used for heavy concentrated load – seldom employed today

Rectangular pad foundation - Used where width of base is restricted

Pad foundation

It provides support to the individual columns

It can be in a circular, square or a rectangular form with a slab of uniform thickness.

It is stepped or hunched to spread the load over a large area

The foundation wall of it can be constructing by using rubble or brick.

Pad foundation

The footing for a single column may be made square in plan, but where there is a large

moment acting about one axis it may be more economical to have a rectangular base. Pad

foundations are used to support an individual point load such as that due to a structural

column. They usually consist of a block or slab of uniform thickness, but they may be stepped if

they are required to spread the load from a heavy column

Figure 5

Figure 12_Pad foundation

Pad foundation

The footing for a single column may be made square in plan, but where there is a large

moment acting about one axis it may be more economical to have a rectangular base. Pad

foundations are used to support an individual point load such as that due to a structural

column. They usually consist of a block or slab of uniform thickness, but they may be stepped if

they are required to spread the load from a heavy column

Figure

11_Pad

foundation

Figure 12_Pad foundation

Combined footing

A combined footing supports two columns

It is used when two columns are so close to each other

It is economical to provide footing like this to two columns rather than individual footings.

A combined footing may be trapezoidal or rectangular in the plan view

By combining with the interior column the load is evenly distributed

Combined Foundations.

A Combined footing constructed for two or more columns is call as a combined footing.

Raft foundation

A raft foundation is continuous in two directions, usually covering an area equal to or greater than the base of a building or structure. Raft foundation are used for lightly loaded structures on soils with poor bearing capacity or where variations in soil conditions necessitate a considerable spread of the load, for heavier load in place of isolated foundation, where differential settlements are significant and where mining subsidence is likely.

Figure 6

Fig No-07 Raft foundation

raft foundation is divided 2 types

1) Solid slab raft foundation

2) Beam and slab raft foundation

Discussion

The proposed building is had a basement and 7 floors. When the soil weaker and compressible. Raft foundation is most suitable this site.

Mat or Raft foundation

A raft foundation is continuous in two directions, usually covering an area equal to or greater than the base of building or structure. Raft foundation are used for lightly loaded structures on soil with poor bearing capacity or where variations in soil conditions necessitate a considerable spread of the load, for heavier loads in place of isolated foundations, where differential settlements are significant and where mining subsidence is likely.

ADVANTAGES OF RAFT FOUNDATION

1.This foundation type is suitable for when the soil at site is soft and marshy

having uncertain behaviour. Raft foundation eliminates the possibility of

differential settlement.

blinding

r.c upstand beam in 2 direction

reinforcement bars

distrebutionbar

2.Overall settlement of the struture is reduced, as the total load of the Structure is distributed over a large area and thus intensity of pressure on the foundationsoil is reduced to minimum.

3.Ditribution of load on entire area of foundation is uniform.

Slab and Beam raft foundation

As a foundation to support the heavier load of walls or columns a solid slab raft would require considerable thickness. To make the most economical use of reinforced concrete in a raft foundation supporting heavier loads it is practice to from a beam and slab raft. This raft consists of upstand or downstand beams that take the loads of wall or columns and spread them to the monolithically cast slab which can be excavated no need the timbering to trenches it is economical to use down stand beams.(Figure:04)

(Figure:04)

Cellular raft foundation

Where the differential settlement are likely to be significant and the foundation have to support considerable loads the great rigidity of the monolithically cast reinforced concrete cellular raft is an advantage. This type of raft consists of top and bottom slabs separated by and reinforced with vertical cross ribs in both directions. The monolithically cast reinforced concrete cellular raft rigidity and spreads foundation loads over the whole area of the substructure to reduce consolidation settlement and avoid differential settlement.

A Cellular raft foundation may be full depth of basement storey and the cells of the raft may be used for mechanical plant and storage.

A cellular raft is also used when deep basement are constructed to reduce settlement by utilizing the over burden pressure occurs in deep excavations. This negative or upward pressure that occurs in deep exaction is negative or update pressure occurs in bat of deep excavation in form of an upwards heave of the subsoil caused by the removal of the overburden, which is taken out by excavation. This often quit considerable upwards heave can be utilised to counteract consolidation settlement caused by the load of the building and so reduce over all settlement.

3.3.3 Raft Foundation

A raft foundation is fundamentally a large combined slab foundation designed to cover the whole or a large

part of the building.

A raft may be used when the soil is weak and columns are so closely spaced in both directions, or carry

such high loads, that isolated column foundations would over lap or would almost complete the site.

Raft foundation are used for lightly loaded structures on soils with poor bearing capacity

Raft foundation

Mat/Raft Foundation

These are used to spread the load of the superstructure over a large base to reduce the load per unit area being imposed on the ground and this is particularly useful where individual column loads are heavy.

The simplest type of raft is a flat slab of uniform thickness supporting the columns. Where punching shears are large the columns may be provided with a pedestal at their base. The pedestal serves a similar function to the drop panel in a flat slab floor. Other more heavily loaded rafts require the foundation to be strengthened by beams to from a ribbed construction. The beams may be down standing, projecting below the slab or they may be upstanding as shown in the figure. Down standing beams have the disadvantage of disturbing the ground below the slab and the excavated trenches are often a nuisance during constructions, while upstanding beams interrupt the clear floor area above the slab. To overcome this second slab is sometimes cast on top of the beams so forming a cellular raft.

Material

Reinforced concrete

Type of excavation needed

Bulk

Number of stories can be construct

Six to seven stories

Structural type of the raft foundation

Type of Raft Foundation

There are four types of raft foundations

1. Flat Plate2. Flat Plate thickened under Column3. Beams and Slabs4. Slab with basement walls as part of the mat

Flat Plate

Flat plane slab rafts are suitable for lightly loaded structures such as small houses. They are also be used for heavier structures if the ground condition is good and no differential settlement isexpected. A flat plane slab raft consists of a reinforced concrete slab, usually slightly larger than the area of the building. Reinforcement in the form of a mesh fabric is provided on both the top and bottom faces of the slab.

Figure 7

Figure 8

Uniform Thickness

Fig-5. Flat Raft Foundation (A) Cross Section A-A (b) Plan View

Flat Plate thickened under Column

Figure 9

AA

(b)

Figure 10

Column

Fig-6. Flat Plate thickened under Column

Beams and Slabs

They are used where poor soil conditions are encountered. The slab and beam provides stiffness and prevents the distortion of the building

Column

Beam

Slab with basement walls as part of the mat

They consist of two reinforced concrete slabs linked by internal walls which divide the void into cells. This type of foundation is suitable where poor soil is encountered at a shallow depth, and where it would be uneconomical to use slab and beam raft foundations

Column

Slab

Figure 11

Walls act as sufficient for the mat

Raft Foundation Sketching

Figure 12

Figure 13

Raft foundation

A mat or raft foundation is a combined footing that covers the entire area beneath a structure & supports all the walls &

columns. When the available soil pressure is low or the building loads are heavy, the use of spread footings would cover

more than one – half of the area & it may prove more economical to use mat or raft foundation. This foundation can be

constructed in several methods. Graphically it is mentioned below.

Flat plate Flat plate with pedestals

Cellular construction Basement walls as rigid frame

Two-way beam and slab Flat plate with pedestals

Figure 06 - Raft foundations

Raft foundation

Raft foundation consists of a raft of reinforced concrete under the whole of the building to the sub soil below the raft used for building on compressible. Ground such as very soft clays. raft foundation two type ,flat raft and wide toe raft flat slab raft is cast on of building concrete and a moisture proof membrane to prevent damp rising through the slab. The ground has reasonable bearing capacity the raft may not to be reinforced. Where the ground has poor compressibility the wide toe raft is recommended the stiffening edge beam being designed as a toe to support the outer skin of brick work. So that the raft is not visible, this foundation used either on compacted leveled fill above the natural ground line as illustrated or in steps cut in to the natural ground.

Figure 15_Raft foundation

Figure 16_Raft foundation

2.DEEP FOUNDATION:- In case of bearing capacity of the soil is very poor and dependingon some other conditions,the structure has to be taken deep in to the soil.

This foundation are mainly two types.

1.Pile Foundation. 2.Caisson foundation.

In building constructionmost commonly uswed type of deep foundation is pile foundation.

DEEP FOUNDATION

When the soil at or near the ground surface is not capable of supporting a structure, deep foundations are required to transfer the loads to deeper strata

Deep foundation

In case of bearing capacity of the soil is very poor and depending on some other

Conditions, the structure has to be taken deep in to the soil. There are mainly two types

Of deep foundation

2. Deep foundations

Deep foundations are used to transfer a load from a structure through an upper weak layer of soil to stronger deeper layer of soil. Deep foundations are also provided for low bearing capacity soil.

Mainly there are two types of foundation:

1. Pile foundation2. Caissons foundation

3.2.2 Pile foundation

Pile foundation as series of columns constructed or inserted into the ground to transmit the loads of a structure to a lower level of subsoil. Also piles define as a long vertical load transferring element.

The pile foundation used in following situations;

Water table level is high Natural bearing capacity of soil is very low. Highly compressible soil layer Subsoil movement.

Based on materials:-

Timber pile Steel pile Reinforced concrete pile

Fig No-08 Pre-cast Pile foundation

Discussion

It is commonly pile foundation is more expensive foundation than other types. 7 storey building was selected to our visit. pile foundation is perhaps need to more than 10 storey building. many apartment buildings are located around the site. if pile foundation is done, those can be effected. so unsuitable.

Pile fondation Pile foundation as series of columns constructed or inserted into the ground to

transmit the loads of a structure to a lower level of subsoil. Also piles define as a long vertical load transferring element.

The pile foundation used in following situations; Water table level is high Natural bearing capacity of soil is very low. Highly compressible soil layer (peat, marshy land and filled area) Subsoil movement.

We can classify the piles,Based on materials:-

Timber pile Steel pile Reinforced concrete pile Pre-cast pile

Based on method of construction:-

Replacement pile Displacement pile

Based on method of load transmission:-

Friction pile:By using the “friction between the pile and surroundings mechanism” transferring the

load of structure into subsoil as friction.This type of pile used for weak soil like clay or silt.(Figure: 05)

End bearing pile:By using the “bearing of piles on hard bedrock at certain depth mechanism” transferring

the load to hard bedrock. (Figure: 06 )

Load

Pile cap

Weak soil

Firm Strata

End bearing pile

Bed rock

Load

Pile cap

Weak soil

(Figure:05) (Figure:06)

Pile foundation

1. Bearing piles2. Friction piles3. Screw piles4. Compaction piles5. Uplift piles6. Batter piles7. Sheet piles8. Anchor piles9. Sheet piles10. Fender piles

PILE FOUNDATIONThe pile foundation is a construction on piles. A pile is an element of construction composed of timber, concrete or steel or a combination of them. Pile foundation may be defined as a column support type of foundation which may be cast in-situ or precast. The piles may be placed separately or they may be placed in form of a cluster throughout the length of a structure. This type of construction is adopted when the loose soil extends to a great depth. The load of the structure is transmitted by the piles to the hard stratum below or it is resisted by the friction developed on the side of piles. In Srilanka mostly bearing piles and Friction piles are being used in construction.

CLASSIFICATION OF PILES

1. Based on material used

Steel piles

Concrete piles

Timber piles

Composite piles

2. Based on mode of transfer loads

En- bearing piles

Friction piles

Combined end bearing and friction piles

3. Based on method of installation

Driven piles

Bored and cast-in-piles

Screw piles

Jacked piles

4. Based on use

Load bearing pile

Compacting piles

Tension piles

Sheet piles

Fender piles

Anchor piles

5. Based on displacement of soil

Displacement piles

Non-displacement piles

Load bearing Piles

These piles penetrate through the soft soil and their bottoms or tips rest on a hard stratum . The soft ground through which the piles pass also gives some lateral support and this increases the load carrying capacity of the bearing piles. These piles act as columns.

Soft material

Fig- Load bearing pile

Rock

Friction Piles

When soil extends to a great depth, piles are driven up to such a depth that frictional resistance developed at the sides of the piles equals the load coming on the piles. The total frictional resistance of piles is obtained by multiplying frictional resistance of soil with the area of pile in contact with the soil. The total frictional resistance can be increased in following ways.

By increasing the diameter of the pile, By driving the pile to a greater depth, By making the surface of the pile rough, By placing the pile closely and, By grouping the piles.

Fig- Friction Pile

Pile foundation

Piles are column like structural elements in a foundation. The function of piles is to transfer superimposed loads through weak compressible strata or through water, onto soils of

adequate bearing capacity or onto rock strata. As the adequate bearing soil or rock strata is at an uneconomic depth, the pile may carry the superimposed loads by skin friction between the pile surface and the soil. Moreover, piles are required to anchor structures against uplift loads and assist structures in resisting lateral and overturning forces from winds or waves.

Figure 17_Pile foundation

Pile foundation

Piles are column like structural elements in a foundation. The function of piles is to

Transfer superimposed load through weak compressible strata or through water, onto

Soils of adequate bearing capacity or onto rock strata. As the adequate bearing soil or

Rock strata is at an uneconomic depth, the pile may carry the superimposed loads by

Skin friction between the pile surface and the soil. Moreover, piles are required to

Anchor structures against uplift loads and assist structures in resisting lateral and

Overturning forces from winds or waves.

Reasons for selection of pile foundation

Pail foundation are most economical

Pail foundation are using soil week area

Piles supported on rock create the greatest bearing capacity.

When the ground floor slab has to be carried the ground, e.g. on a sloping site

Figure 07 - Piles being driven in to the earth

Caissons-

Caissons are a form of deep foundation which are constructed above ground level, then sunk to the required level by

excavating or dredging material from within the caisson. Caissons are usually used in construction of bridge piers and

other structure where the foundation is under water.

Figure 08 - Caissons pier

Factors considered in selecting foundation for our building.

Recommendations given in the 3 Borehole test results Bearing capacity of soil

Bearing capacity of foundation

Time needed to finish the construction

Water table level

Distance to the neighboring buildings

Cost for foundation

Live load, dead load (estimated weight of the building) etc.

In the borehole test report it was recommended to build Raft foundation with an allowable bearing capacity of 200

kN/m2 and an inverted T-type RC strip footings with an allowable bearing capacity of 200 kN/m2 were given as

alternatives.

After that as a conclusion they decided to build a raft foundation. While comparing with other foundations Raft

foundation is the most suitable and the most economical foundation for the selected building. In case if pile foundation

was selected it would have been more costly, sometimes while piling the neighboring buildings might have been

effected due to the vibration, as the water table is very high it would have been difficult to excavate holes for piling.

While building a raft foundation the problems described above will not occur. So I say the selection of foundation for the

building is correct in this construction.

2.2. What Are the Types of Excavation Needed For This Foundation?

Construction? Describe the Associated Temporary Works For The

Construction of Foundation.

Excavation

Excavation is mainly known as removing earth from an area by using machineries or by using tools for digging and

removing the earth form an area. Excavation work is done for various purposes. It can be done for foundation work, for

leveling an area and others. Sometimes after excavation refilling is done in that area, so it is important to maintain the

earth which is removed from that area for further use. In a hill area if the area has to be level the earth which is

removed from the cut piece will be replaced by the area which is empty and made it as same level so the work done in

that area is easy

Types of excavation

There are different types of excavation method used in construction these methods are

Soil strip:- The removable of the

vegetation soil must be removed by topsoil covering by using of machinery.

Reduced- level excavation:- Is done in the areas

where the soil layer is not at the same level. To make it straight or to a same level reduce- level excavation work has

to be done. In reduced- level excavation the soil is cut or removed from the high level area and is filled in to area

where the level is lower than the original level and it is made in to a same level. After that the soil is compacted and

made to a same level. Mostly this type of excavation is done for road process especially in the hilly areas.

Removal oftop soil

Cut

Fill

Formation Level

Formation Level

Figure - 09- Shows the reduce level excavation

Bulk excavation: - In this excavation large

volumes of sub soil is removed and it is known as bulk excavation. This type of excavation is mostly done for

various types of foundation and basement areas.

Trench excavation:- To excavate or

filled to the formation and it is necessary to excavate trenches to a lower level. In these trenches the foundation

of a buildings are constructed. It is also required for the usage of other services like water, electricity etc…

Figure - 10 :- Show the method of excavation

Trenchexcavation Deep trench

excavation

Trail pithole

Bulkexcavation

Figure - 10- Shows the method of excavation

Hole or pit excavation:- This type of excavation is

mostly done for pile foundation. For this holes or pit are excavated by the methods of drilling. Sometimes pit

excavation may be done by hand and also it may in shallow rectangular shape.

Water excavation:- Once the soil is dug or

excavated deeper than the ground water level the water has to be remove from that area. This removal of water

from the excavated pit is called dewatering. Dewatering is done by the usage of a pump at the bottom of the

excavated pit.

Type of excavation used in my site

They selected the bulk excavation

They did the disposal activity.

They removed the un wanted trees, bushes and tree roots on the surface

They started the excavation using JCB excavator.

In the site Soil investigation report.

Case1- With ground improvement

.The same allowable bearing capacity of 200kN/m can be adopted, if ground improvement is carried out as indicated

below.

It is recommended that the ground improvement method within building areas where a raft foundation would be

adopted is to first support the building boundaries with adequate shoring. Thereafter, starting from one boundary,

ground improvement should be carried out in a series of trenches. In each trench, the excavation is carried out parallel

to the boundary using a backhoe to a depth of 3m. the excavation should then be filled back up to final design ground

level. The backfill can be with later tic gravel. This should be placed in layers and compacted with several passes of a

roller with the soil maintained at or near its optimum moisture content.

Case2- Without ground improvement

A reduced value for allowable bearing capacity can be recommended, if information is provided on the depth of the

basement raft. The recommendation for this parameter could vary between 125kN/m and 200kN/m

It is recommended that adequate shoring be adopter when excavating alongside the existing structures. An example of

such a system could consist of.

(1) driving steel 1-sections, which are palace at 0.9m centers, to a depth of about(3-4)m along the boundary for the

excavation.

(2) Excavating and placing timber planks between the 1-sections.

(3) Supporting the boundary 1-sections at a depth of 0.6m using an internal support system. This could be done by

welding lateral sheet piles at 0.6m depth of the verticals along the boundary, and then providing support to the

lateral sheet piles at suitable intervals.

Selected foundation in the site

In the research site the type of foundation selected is shallow foundation. This foundation is selected depending on the

soil report. The engineers who had done the research has recommended for a shallow raft foundation.

The engineers have recommended the depth where the foundation should be laid. It should be laid up to a

minimum depth of 2.5meters.

It bearing pressure e the building can bear is 200kN/m2.

Finally selected raft foundation in the site.

Pile foundation may be used for this construction. Because this is a five stories building and pile foundation will give more strength for proposed building than raft foundation

Easy to construct

Economically less than pile foundation

It makes Less pollution to environment than pile foundation

It reduces the differential settlement on non- homogeneous soil

Selected site soil is a high bearing capacity of sand

This raft foundation is selected for the building by the engineers after considering the ability of the artificial foundation

to support the weight of the structure together with all the loads acting on the building

The ability of the natural foundation to carry the loads of the foundation without any deformation. Determining the

major factors considered in the ability of natural foundation to carry all the loads of the building into the different layer

of the soil.

Ability of the structure to carry on the small movements at the foundation level, without damaging the load bearing

capacity of the structure. Some buildings are designed in a way to bear small movements which comes to the soil but it

is difficult for raft foundation to bear the impact of an earth quake. Ground movements can occur due to the mining,

lowering of the ground water table, increasing the level of ground water table freezing of moisture underground etc…

temporary works in the site.

In this task the site selected is no25, Galle Road, Wellawatte. In this site the method of excavation done was bulk

excavation and shoring method done was timbering. First they inserted 8 feet of H irons with an even distance of 3 feet.

Then the soil is excavated for 5 feet by the using a back actor and 3feet by 10 inches by 2 inches wooden planks are

inserted in between the H irons. Like this shoring is done bit by bit and the whole area is covered. After finishing the

timbering then the soil is compacted by using a compact machine. Soil is compacted by using a manual vibrator. Once

the soil is being well compacted then the damp proof material is spread and 2 inches screed concrete is laid on top of it.

After this the reinforcement is arranged and after this concrete foundation is laid. Once the foundation is set then again

the reaming of the excavated soil is laid on top of the foundation bed

2.3. Describe The Construction Method Of Foundation At Your Visited Site

Stating All The Main Steps.

Method of construction of foundation

The site was cleared and after drilling three bore holes the soil investigation test was done.

Depending on the soil investigation test the structural engineers recommended a shallow foundation in the

site.

So first the top soil is removed from the site and bulk excavation was started.

During excavation shoring process also started and the whole area was excavated and shoring was

completed.

Then the whole site was sprayed with pesticides to kill all the living insects and organism in the soil of the

site.

The whole soil of the site is compacted by using manual vibrators. Once the soil is fully compacted they had

spread polythene sheet over the compacted area. These sheets are over lapped in about 1 feet and the

whole area is covered with the sides.

Then 2 inches screed concrete is laid on top of it and kept of settling. Screed concrete layer is 1: 3: 6.Once it

is set the next procedure begins which is the arrangement of reinforcement.

The reinforcement is bind as per directed by the engineers. Most of it is bind as per the measurement given

in the drawing ie:-Y25-55-5B. The bars are made by tor steel and it is binded with links of mild steel at the

given measurements.

Then cover block of 100mm by 100mm is laid on the screed concrete where the reinforcement is to be

place. Mainly this is done so that the reinforcement and the form work will have enough space in between.

After laying the reinforcement as directed on the drawing then concrete is poured on top of it. In the site

they used readymade concrete grade 1: 2: 4. This was poured slowly and carefully to avoid concrete from

segregation.

Once the concrete is poured then it was compacted by using a porker vibrator. The concrete was vibrated

properly so the air trap inside will be removed from the concrete. If it is there then the problem of

segregation and bleeding will occur. These are the signs of poor concrete.

Once the vibration of concrete is finish then it is kept for setting process. During this process they had filled

the whole foundation with water and kept it for 21 days.

Water is poured on the concrete to prevent the heat which rises in the process of hydration so that the

concrete will go through its own setting time in the required condition.

After 21 days the water is emptied from the foundation and the form work of the foundation is removed like

the beams covering the foundation.

The empty spaces inside the foundation are filled with soil. And the construction of the rest of the parts

starts again.

Figure 11- shows the raft foundation

Any structure in general is considered to have two parts the sub structure and super structure,

the sub structure transmits the load of super structure to the underlying soil and is termed as

foundation. This is the most important part of any structure. Since it remains important generally

embedded ground any sign of failure of foundation is not noticeable till it has already affected the

structure if any part of the structure incepts foundation. The foundation by adopting suitable

measures. But if foundation of a structure has yielded and ruptured it is very difficult to make it good.

Objective of foundation

Foundation is provided for the following purpose;

1. To distribute the load of structure, on large area, so that the intensity of load does not exceed the safe bearing capacity of the underlying soil.

2. To distribute the load on underlying soil evenly and thus to prevent unequal settlement of the foundation.

3. To provide a level and hard surface for the super structure to be build over it.

4. To increase the stability of the structure as a hole, against sliding, overturning or other disturbing forces like wind, rain etc.

5. To prevent lateral movement of the supporting material, so that the safetyof the structure is not endangered.

The factors to be considered in foundation

Loading requirements

Soil investigation report is given for seven storey semi-luxury building. So, building load is very high.

Figure 18_Loading requirement of a building

Water table level

If water table level is very high, pile and raft foundation is very difficult to do and special type of dewatering method is necessary.

Figure 19_Water table level

Structural load of the building

So many loads are acting in a building. The foundation should be enough strong to support for all loads. Mainly there are three different types of loads acting in a building such as.

Figure 20_Structural load of the building

Construction cost

Pad or strip foundation is recommended in soil investigation report. Pile or raft foundation may be used for this building. But client wants to reduce the building construction cost.

When pile or pad foundation is selected, machineries and equipments have to be used. So it will affect the construction cost.

Time needed to finish the construction

Pile or raft foundation is taken more time than strip or pad foundation to construct the foundation. Client wants to finish the work before particular date.

Weather condition

Pile or raft foundation is very difficult in rainy season. Latest dewatering pumps are needed to dewatering. It may affect the construction cost.

Finally I selected Raft foundation

Compare with the other foundation raft foundation is the most suitable one to construct the building,

because has good qualification rather than the other.

Figure 21_Raft foundation

Why didn’t I choose pile foundation

Spend more time & money for labours and materials. Pile foundation depends on machineries. These are used to perform the water and mud from the pile. Need more labours. In rainy season can’t construct the pile foundation. Because the flood level will be

increase.

Constructing time period will be enlarging.

When the pile hammer was drop to the pile, surrounding place vibration will occur. So this will damage the

adjacent buildings. The jacking method piles can drive

into the ground with a smaller vibration to the land. This can be done with help of an air pumping machine, but this method is expensive.

Figure 22_Pile foundation

Why didn’t I choose pad foundation

Also, pad foundation is not suitable for this building. As,

It’s not suitable for filled areas. In this case around half of this land is covered by peat soil. It is removed and refilled. So, pad is not suitable.

This land has silty clay soil type. It is a very loose soil. For silty clay it is not suitable.

Excavation

When the building is built, first the ground wants to excavate. Because the excavation is necessary for construct the building until some stratum is reached which will support the total weight of the building when it is fully occupied.

Type of excavation

Soil strip excavation Reduced-level excavation Bulk excavation Trench excavation Hole or pit excavation

Soil stripBy this method, the vegetable soil must be removed before any other excavation takes place.

The process is to strip the surface of the ground of its topsoil covering. Bulldozer, Scraper, Back-actor, Mechanical shower and Skimmer are the machineries those used to carry out this excavation method.

Soil strip excavation Top soil includes plans, animal and decaying matter which makes the soil compressible and

therefore unsuitable for supporting buildings.

Figure 23_Top soil excavation

Reduced level excavationOn a sloping site, it may be necessary to cut into the banking on one side of the proposed building, while filling with suitable material on the other side, in order to achieve the level working surface of formation level.

REDUCED-LEVEL EXCAVATION

Figure 14

cuting cuting

filling

fromation level

Reduced Level Excavation

It is usually necessary to provide a level surface from which construction may take place, and this level may be lower than the top of the existing soil level. In such cases, excavation will have to be carried out in order to reduce the level of the ground. If the available material is suitable for filling purposes, this excavated material can be used to fill the other part if the construction work is going on a sloping land. Bulldozer, Motor grader or excavator can be used for this type of excavation.

Figure 24_Reduced level excavation

Bulk excavation Bulk excavation is required when, where large volumes of subsoil are required to be excavated

in order to reach the formation level. This type of excavation may be reduce levels or to provide basement areas. Large machineries use for this type of excavation.

Figure 25_Bulk excavation

Bulk excavationWhere large volumes of subsoil are required to be excavated in order to reach the formation level, the excavation is known as Bulk excavation. This type of excavation may be to reduce levels or to provide basement areas. In addition to the plant already mentioned, a face shovel may also be used for this type of work.

Trench excavationHaving excavated or filled to a formation level, it is frequently necessary to excavate trenches to a lower level. In these trenches the foundations of the building are constructed. Trenches are also required outside the building for the laying of pipes and cables which carry gas, water , electricity and other services.

TRANCH EXCAVATION

Trench Excavation

After preparation of formation level, it may be necessary to excavate trenches for the

foundations. Trenches are also required out site the building for the laying of pipes and cables

for supplying utilities. This can be done manually or using a backhoe wheel loader. If there is

considerable width, excavators also can be used.

Figure 15

Figure 26_Trench excavation

Hole or Pit excavation

These types of excavation widely used for laying pad foundations. Hand mechanically driven augers or drills are used commonly for excavation. Pits small shallow holes, may be excavated mechanically or by hand.

Figure 27_Hole or Pit excavation

The method of excavation at the selected site

The proposed foundation is raft, because of that they selected the bulk excavation

They did the disposal activity.

They removed the un wanted trees, bushes and tree roots on the surface

They started the excavation using JCB excavator.

While, they excavate they did they proper shoring to the land.( shoring is briefly discussed on the shoring )

They planned to do the excavation and construction part by part, Because of it is somewhat easy.

Associated temporary works for the construction of foundation

Water supply Water is wanted for drinking, mixing cement and etc. So water supply is most

important.

Electricity supply Electricity is very important to work with machineries and equipments.

Shoring

If the soil will be loose, shoring is very important. Generally shoring is done by timber. Shoring protect from soil collapsing.

Labor safety

Labor health is very important, so therefore labours and others wear safety boot, hard hat, safety glues and etc.

Form work Therefore at the site almost timber is used for form work. As well as steel also is

used at the site. But steel is better than timber because it has some good properties.

Task 2.3

Describe the construction method of selected foundation type stating all the main steps.

Construction steps of the Raft foundation

Clearing the site

Site clearing the construction in following ways

Grass, small trees, hills, hillock and bushes etc were removed inside of the land.

Foundations, drainage works, septic tanks, pit-type, latrines and soak pits of the old building

were cleaned.

Underground electric or telephone cables as drainage or water supply lines checked.

Figure 28_Site clearance

Setting out Setting Out a Framed Building

Figure 29_Setting out

The bulk excavation was done at the site.

Figure 30_Bulk excavation

Dewatering process was carried out.

Figure 31_Dewatering

Compaction of the excavated area was done.

Figure 32_Compaction

The concrete screed was placed.

Figure 33_Concrete screed

The formwork for raft foundation was done.

Figure 34_Formwork for raft foundation

A Damp proof membrane was applied; here they used bit more carpet.

The reinforcement arrangements for the raft beam were done.

Figure 35_Reinforcement beam arrangement

The cover blocks between formworks and reinforcement arrangements were placed.

Figure 36_Cover blocks

The column position was set and the reinforcement for column was arranged.

Figure 37_Reinforcement column arrangements

The Grade-25 concrete was poured into formwork to a thickness of 800 mm and it was well compacted by poker vibrator.

Figure 38_Compaction by poker vibrator

After 24 hours the curing process was started and was continued for 7 days.

Figure 39_Raft foundation

Conclusion

Foundation is very important to construct any building. It should be done according some steps that should be carried out for the construction work.

Clearing the site, setting out, bulk excavation, disposal of excavation materials, compaction, damp proof course, form work, screed concrete, and reinforcement arrangement and placing concrete, the steps in the process of constructing a foundation have been clearly identified and described clearly.

Why did they choose Raft foundation?

According to my site

Selection of most suitable foundation

@Strip foundation and pad foundation are not suitable for this building. Because

They are most suitable only for light load structure, but this building is a seven storey

building.

@I didn’t recommend the pile foundation for this building. Because

If that cast-in situ pile foundation

Mainly depends on machineries and equipment such as

Hole drilling machine (BG 27)

Water pumps and trimmy pipes (to carry out the water and mud from the pile)

Needs more skilled labors, such as

1. Bar benders

2. Welders

3. Machine operators

4. Normal labors

Have to spend more money to shoring materials

Bentonite is not available in Sri Lanka so we have to import it. But we can re-cycle it.

(In the case of soil is clay type we don’t much shoring materials)

Have to place the pile on exact position, other wise we have place another two piles instead of that. It

will increase the spends. But we can find out the exact position by proper surveying only.

It gets more time

We can’t construct in rainy season

If that precast pile

While hammering If there any obstacle that will be a major problem

Difficult to place the pile on exact position

While hammering pile, if the pile broke, we have hammer two piles instead of it.

Difficulty transporting the piles

The major problem in pre-cast pile foundation is vibration effect. Vibration can damage the adjacent

building. If there any damage occurs in adjacent building we have face severe law problems or have to

pay big amount to damages.

When we hammer the piles, there would be a big noise, it makes the environmental pollution and disturb

the people

Problem in getting hammer machine

Because, in Sri Lanka only four companies the that machine

So, more suitable for selected building is raft foundation, because of the following reason,

More economical than pile foundation

It makes Less pollution to environment than pile foundation

Some what easy to construct

It reduces the differential settlement on non- homogeneous soil

Recommendations for foundation in my selected site

In my site they selected a raft foundation for their construction work. Because of following.

Due to the some what loose conditions of the sand encountered near the surface the foundation for the

proposed building should be placed at a depth greater than 1.5 m.

Considering above mentioned reason we should go for a pile or raft foundation. But here I recommend for

the raft foundation. Due to the reason as follows,

It reduces the differential settlement on non- homogeneous soil

Suitable for this filled with ruins area

More economical than pile foundation

It makes Less pollution to environment than pile foundation

Some what easy to construct

If building ruins are encountered during the excavation for foundation all that should be removed and

replaced by sand and compacted adequately to bring to a level surface.

An allowable bearing capacity of 150 kN/ m2 could be recommend on a raft foundation placed at a depth of

1.5 m.

These excavations can be done by back co, bulldozer, scraper, and shovel. (Fig:-)

Pit excavationThe design of the substructure may require pits to be excavated. In the case of circular holes, hand or mechanically driven augers or drills are used. Pits, being small shallow or rectangular holes, may be excavated mechanically or by hand.

Excavated land must be refilled by good soil. While refilling, the good soil has to be compacted layer by layer to increase the bearing capacity of the soil. The refill should be done up to the foundation level. Normally foundation level is taken as 3’. Again make sure the soil is compacted well.

As it is planned to construct the building on Combined Pad foundations where large volumes of subsoil are required to be excavated to get the formation. Bulk excavation is suitable to stop soil falling from the sides of excavations due to external forces.

In my site bulk excavation has been made because of soil and water table level

Temporary supporting system for construction of foundation

(1) Shoring method(2) Dewatering

The following chart illustrates the types of shoring.

Fly shoring

Fly shoring is also known as horizontal shoring Flying shore are used to provide lateral support temporarily to the parallel face of building or excavation which have become unsafe. Figure 49 shows a arrangement of a single flying shoring

Figure 16

"Fly shoring"

Fig.11

. Single flying shore

Dead shoring

Dead shores are consisting of horizontal members known as needles and vertical bullies. Dead shores are used under following circumstances;

i. Foundation of the structure is weak and it has to be strengthened or depend without demolishing the whole of the structure.

ii. Lower part of the wall has deteriorated and has to be replaced by new wall. Following figure 50 shows the arrangement of a dead shoring

Figure 17

"Dead shoring"

Rake shoring

It is an arrangement of giving temporary support to an unsafe wall or any structure. Figure 51 shows the arrangement of rake shoring

Figure 18

"Rake shoring

Fig-14 (shoring)

Dewatering

Dewatering is used to improve the run off of ground water to maintain the water table at some depth below the surface.

Why do we have to do dewatering?

To improve the stability of the ground To avoid the surface flooding To alleviate or avoid dampness in basements

Types of dewatering method

Table 1 "Types of dewatering"

Figure 19

Permanently dewatering

Sheet piling

Soil type - Suited for all types of soil except boulder beds

Uses - All types of construction (Practically unrestricted)

Figure 20

"Non anchored"

Figure 21

"Anchored"

Advantages

1. Rapid installation2. Steel can be either permanent or recovered3. Seal may not be perfect

Disadvantages

1. Difficult to drive and maintain seal in boulders2. Vibration and noise3. High capital investment if re-usage is restricted

Diaphragm walls

This is a high strength earth retaining structure

Soil type - Suited for all types of soil including boulder beds

Uses - Deep basements, Underground car parks, Underground pumping stations, Shafts, dry docks

Figure 22

"Diaphragm wall"

Advantages

1. Can be designed to form part of a permanent structure2. Minimum vibration and noise3. Treatment is permanent4. Can be used in restricted space

Disadvantages

1. High cost often makes it uneconomical unless it can be incorporated into permanent structure

Grouted members

Use cement, chemical, resin, bitumen

Soil type- Fissured/cavity and jointed rocks, Sands and gravels where soil particlesare too small for cement grouting

Uses - Filling voids to stop water flow, filling voids to exclude water, to formrelatively impermeable barriers - vertical and horizontal

Figure 23

"Grouted"

Advantages

1. Equipment is simple and can be used in confined spaces2. Treatment is permanent3. Can be used in conjunction with clay/cement grouts for treating finer strata

Disadvantages

1. Treatment needs to be extensive to be effective2. A comparatively thick barrier is needed to ensure continuity3. At least 4m of natural cover is necessary4. High costs and therefore usually economical only on larger civil engineering works5. Required strict site control

Temporary dewatering

Sump pumping Suitable for smaller depths up to 7.5m Water should be pumped more than a rate of filling the pit By pumping pit can be kept empty for particular period of time. And constructions should be completed

in that particular time period. Dispose the collecting water at the distance away from the site to not effect the ground water

movements. Suitable for gravels and sandy soil.

Figure 24

"Sump pumping"

Advantages

1. Simplest pumping equipment

Disadvantages

1. Fines easily removed from ground2. Encourages instability of formation

Well point system

Drains laid on one or more sides of a building intercept the flow of ground water.

Ground water (land) drains are laid in trenches at depths of 0.6 m to 0.9 m in heavy soils and 0.9 m to 1.2 m in light soils. The nominal bore of the pipe is usually 75mm and 100mm for main drains and 65mm or 75mm for branches. The pipes should be surrounded with the clinker, gravel or rubble covered with inverted turf, brushwood or straw to keep fine soil from the pipe.`

Figure 25

"Well point system"

Advantages

1. Quick and easy to install in suitable soils2. Economical for short pumping periods of a few weeks

Disadvantages

1. Difficult to install in open gravels or ground containing cobbles and boulders2. Pumping must be continuous and noise of pump may be a problem in a built up area

Identify and state the method of construction of the foundation selected for your building

Introduction

After finishing the borehole test according to that at the site contractor used raft foundation. Before placing the foundation they have to prepare the site and have to do some arrangements.

According to the site before placing the foundation they have work according to some steps.

Method of construction of the foundation Clearing the site: - In this contactor have to do lot of work. Because there is a 2 story building in the no

25 galle road wellawata. So they cleared off these building. After disposing some brick are taken and used to some store rooms to store the materials. And other unwanted thinks are disposed. At the same time top soil also disposed

Setting out: - After the site clearance and according to the structural designers design the building structure was marked in the land.

Bulk excavation: - According to the raft foundation bulk excavation was done at the site with the use of backhoes and dig up to 2M depth.

Disposal of excavation materials: - With the use of trucks from the site materials are disposed at the site.

Compaction: - After disposing the materials excavated land was compacted with some vibrator machines (Vibrating Rammer).

Formwork: - At this time form work was done for temporary use. And it was done with the use of plywood’s.

Screed concrete: - Concrete was put for the basement of the vibrated land. Reinforce arrangement: - After the concreting work reinforcement arrangement was done. According to

the borehole result raft foundation was used at the site. So reinforcement arrangement also done for raft foundation.

After arranging the reinforcement concreting work was done by the use of plumbing method. After placing the concrete after seven days, concrete work was cured by the use of some gunny bags. ( AN ESTIMATE IS GIVEN SETTLEMENT OF FOUNDATION OF WIDTH 23 m, WHICH

PLACED AT A DEPTH OF 3.0 m )

Fig 12- Reinforcement arrangements for raft foundation Describe different types of Foundation

3.1 Foundation

Foundation is one of the most important elements of a building and which have direct contact with the

ground.

It is the lowest part of a structure which transmits the load of the structure together with live load and the

pressure to the material on which the structure rests in such a manner that the underlying material is not

stressed beyond its safe bearing capacity.

Generally foundation is placed below the ground level to increase the stability of a structure or building

Foundation

Fig no-01

(Sources: http://www.shef.ac.uk/content/1/c6/08/23/07/Research%20Building%20Foundation%202.JPG)

The choice and design of foundations depends mainly the following factors should be considered.

The total load of the building

The nature and bearing capacity of the subsoil

Water table level

Economical factors

Natural hazards

Availability of draw materials

Availability of services

(Sources: http://www.jacek.co.za/files/1(big).jpg /...)

TASK#4

Identify and discuss various factors considered in selecting a foundation type and justify the selected type of

foundation for the building selected

4.1. Factors

Select foundation depends on many factors such as

1. Magnitudes of the loads,

2. Nature of the supporting soil,

3. Site conditions,

4. Potential natural hazards,

5. Climatic conditions

6. Settlement of the soil

7. water table

8. landscape contour (slope of site)

9. Cost

10. Accessibility

4.2. Justify selected foundation

This apartment have six storied building and soil structure having low bearing capacity, So foundation should

have more strength and shear force. When considering stories and soil capacity can go for Strip and Raft

foundation, but cannot go for pile and pad foundation. Because of there is six stories building and no need too

much of strength of foundation for this type of building. If it is selected this is uneconomical way of selecting

foundation.

Table No- 02 Comparison of Strip and Raft foundation

Factor Strip Raft

1)Low bearing sub soils Suitable More suitable

2)Multi store building Suitable (up to 4/5 stories) Suitable (up to 8/9 stories)

3) Cost of construction Low Low

4)Special machineries and No need No need

skilled laborers

5)Affect the adjoin building

during the excavation

little little

6)Going deep for foundation No need No need

7)More working space No need need

The site is located, Galle road frontage area the bearing capacity of the soil is very low and building is resided near the

road and beside the sea. Vibration and wind load also should consider. Raft foundation is selected from the evaluation of

strip and Raft foundation. More Justifications for the selection of Raft foundation have been described below. The most

influence cause is the type of soil, total load of the building, and water table level.

Raft foundation are required on soil of low bearing capacity, or where structural column or other loads

areas are so close in both direction that individual pad will nearly touch each other. The function of

raft foundation are to spread the load over as wide an area as possible, and to give a measure of

rigidity to the sub-structure to enable it to bridge over local areas of weaker or more compressible

soil. The degree of rigidity given to the raft also reduces differential settlement. It is useful in reducing

different settlement on variable soils or there is a wide variation in loading and adjacent column or

other applied loads. They are often needed on soft or loose soils with low bearing capacity as they

can spread the loads over a larger area.

TASK#5

Describe the method excavation and the associated temporary work carried out at your site

5.1. Excavation

Excavation is removing soil from earth. It is major planes in construction excavating machines come

in a wide variety of designs and size. Excavation can do hands or machines.

Excavation method depends on,

Nature of the subsoil

Purpose of the excavation – determines the size

Presence of ground water

Location of the excavation – impose certain restrictions

Availability of the plant and the site limitation; e.g. size, presence of large number of services which restricts the

movements of the plant

Fig: 10 Excavations

(Sources: http://keywestcivil.com/ESW/Images/digging_1.jpg)

5.2. Excavations classification

1. Shallow – 1.5m deep

2. Medium – 1.5 to 3.0 m deep

3. Deep – over 3 m deep

5.3. Types of excavation

Reduced level excavation

Hole excavation

Bulk excavation

Soil strip

Trench excavation

Foundation and its suitable excavation are given below

Pad foundation - Trench and Pit excavation

Strip foundation – Trench and Pit excavation

Raft foundation – Bulk excavation

5.3.1. Reduced level excavation

Carried out below over site level to from a level surface on which to build and can consist of both cutting and filling

operations. The level to which the ground is reduced is called the formation level.

Fig: 11 Reduced level excavation

(Sources: http://www.frankissolutions.com/images/croydon.jpg)

5.3.2. Hole excavation

The design of the substructure may require holes to be excavated. This type of excavation can be carried out hand

mechanically driven augers or drives are used pits, being small shallow or rectangular holes may be excavated mechanic

or hand.

Fig: 12 Hole Excavation

(Sources: http://www.accumark.us/Subsurface_Utility_Services/jpgs/pht_testhole_excavation.jpg)

5.3.3. Bulk excavation

Where large volumes of subsoil are required to be excavated to reach the formation level the excavation is called bulk

excavation. This type of excavation may be reducing levels basement areas.

Fig: 13 Bulk Excavation

(Sources: http://www.marsbuild.co.uk/images/groundworks.jpg)

5.3.4. Soil strip excavation

This function is before the excavation, the vegetable soil remove form the land used by bulldozer, drag line, scraper,

backactor and skimmer

Fig: 14 Soil Strip

(Sources: http://wwwdelivery.superstock.com/WI/223/1555/PreviewComp/SuperStock_1555R-147050.jpg)

5.3.5. Trench excavation

Having excavated or filled to a formation level, it is frequently necessary to excavate trenches to a lower level. In these

trenches the foundations of the building are constructed. Trenches are also required outside the building for the laying

of pipes and cables which carry gas, water, electricity, and other services, used by trench hoes, wheel ditchers and

backactors.

Fig: 15 Trench excavation

(Sources: http://www.amwestcon.com/Images/Bromley%20F102%20-%20Trench%20Excavation_website_photo.jpg)

5.4. Evaluation

When considering this site, the type of sub soil, the ground water level most suitable excavation is trench

excavation .Because our site suitable foundation method is strip.

When we considering above these factors, strip foundation is most suitable for this construction , this apartment

have six story building and soil structure having very low bearing capacity, so the soil structure should bear six

story building load , so foundation should have more strength and shear force . That’s why strip foundation is

most suitable. So, suitable excavation method is trench. This site can use pad foundation because of soil bearing

capacity, water level and soil report recommended shallow foundation and foundation depth 2.0 m. if we select

strip foundation. Cost will reduce excavation and suitable

These are used to small story buildings. That’s why we can’t do bulk and Pit excavation. We can’t use pile foundation

excavation. Because when we use the pile foundation we need more space and more machinery facilities. But these

sites have small area. Pile foundation provides high cost. So we can’t use hole excavation. Trench excavation method is

correct and suitable for this site.

This is a method temporarily supporting system of structures or sides of excavation by shores

5.5. Shoring

This is a form of temporary support which can be given to existing building with the primary function of providing the

necessary precautions to a void damage to any person from collapse of structure as required by the construction

regulation 1996.

Fig: 16 SHORING

(Sources: www.galligroup.com/images/shoring.jpg)

5.6. Types of Shoring

Ranking shoring

Dead shoring

Fly shoring

5.6.1. Ranking shoring

This is a system of giving temporary support to an unsafe wall. . The centre line of the ranker should intersect with the

centre lines of the wall

5.6.2. Dead shoring

This is the system of shoring which is used to render vertical support to walls and roofs, etc.

5.6.3. Fly shoring

It is a system of providing temporary support to the party wall of two buildings where the intermediate building is to be

pulled down and rebuilt.

Fig: Fly shoring

(Source: http://www.jasco-sales.com/pages/prodpgs/general/wall.JPG)

5.7. Analysis

There are different types of shoring methods are available. But this selected site most suitable shoring method is raking

shore. We consider Flying or horizontal shores this is not exceeded 2 m. But our site span is greater than 2 m. So we

can’t do this method. We consider dead shores this method carried out only vertical loads. So, this method also not

suitable in my site.

Considering all things (Space for surrounded building, Load) the most suitable method is raking shore.

(Sushil kumar, 2003)

Task#6

Identify and state the method of construction of the foundation selected for your site

6.1. Method of Construction of the Foundation

6.1.1. Pre construction process

1. Plan

Should plan the building’s layout properly and decide on the specification for each major item of work so that

the cost of construction can be kept within the estimated value.

Man power – skilled, semi skilled and unskilled

Materials – cement, sand, metal, steel etc

Construction shed – warehouse for materials, office and workers accommodation

Utilities

Wastages – what to do with excavated soil & other wastages

Fore seeing – problems to be faced and possible sudden problems such as heavy rain, accident, storm may arise

Controlling man power and material with related to time, economy and efficiency

2. Site Clearing

Surface cleaning such as grass, trees, hillock etc

Obstructions cleaning above or below the ground such as old drainage, old foundation, soak pit

3. Layout/Setting out

Creating a boundary line by using robes and pegs

4. Soil Investigation –

Borehole, soil test reports.

Type of excavation can be selected from the soil investigation report

6.1.2. Construction Process

5. Top soil excavation

To remove top of soil because of that soil is not strength

Fig: Top soil excavation

(Source:   http://www.tasexcavation.com/ / )

6. Pit excavation

Fig: Pit excavation

(Source: http://www.trainmuseum.org/Volunteers/Pit_1_excavation.jpg  )

7. Earth work Support

If soil is loose, can use Earthwork support

Fig: Earth work support

(Source: http://www.pjread.co.uk/work/carpark1.html)

8. Compacting bottom of surface

Fig: 22 compacting bottom of surface

(Source: http://montpelierrestoration.files.wordpress.com/2008/08/thomas-compacting-

path_mg_8155158132008.jpg)

9. Dewatering

There is ground water, so they have done dewatering

Fig: Dewatering

(Source:    http://www.mashburnconstruction.com/Newton%20Farms/Newton_farms_september_2004.htm)

10. Placing blinding/ Pour screed concrete

Grade 20 was used cement: Sand: Coarse Aggregate and curing should be carried out for 7 days

Fig: Placing blinding

(Source: http://www.rawell.co.uk/media/enlargements/waterproofing/blinding-pic10.jpg)

11.  Fix Reinforcement bars and placement of foundation steel

Fig: Reinforcement bars

(Source: http://picasaweb.google.com/lh/photo/4XzFqyLBvR3tc6Ab4UL-Bg)

12. Fixing of shuttering/Formwork

Fig: Formwork

(Source: http://www.builderbill-diy-help.com/raft-slab.html)

13. Pour concrete to foundation

Fig: Pour concrete

(Source: http://moladi.com/moladi.htm)

14. Compaction

Sufficient compaction should be carried out

Fig: Compaction

(Source: http://moladi.com/moladi.htm)

15. Curing for 14 days

Fig: curing

(Source: http://www.builderbill-diy-help.com/image-files/curing-concrete.jpg)

16. Placing Damp proof membrane

Fig: Dam proof membrane

(Source: www.themonument.info)

17. Remove all formwork and support material

18. Placing of screed

Fig: Placing screed

(Source: http://www.themonument.info)

Types of foundations

Foundation is the lowest part of the structure at the ground level which is indirect contact with the ground.Foundation transmits all the dead / live loads to the soil on which the structure rests.

Factors considering in selecting a foundation type. structure load of the building Bearing capacity of the soil ground water table level Weather condition Cost of the construction

These are the functions requires of a foundation Sufficient strength to bear load of the structure without any damage. Durability

Resistant to water Resistance to vibration Resistance to high temperature Reduce settlements

STRIP FOUNDATION

Strip foundations consist of a continuous strip, usually concrete formed centrally under load bearing walls. The continuous strip serves as a level base on which the wall is built and is of such width as is necessary to spread the load on the foundations to an area of sub soil capable of supporting the load without undue compaction. We are using strip foundation for light load structures. It is provided for a load-bearing wall and also provided for a row of columns which closely spaced that their pad foundations over lap or nearly touch each other.

Materials Mass concrete / Rubbles

Type excavation needed Trench

Number of stories can be construct Single or two storey

Structural type of the element Bar / rod elemen

PAD FOUNDATIONWe are using pad foundation for little higher loads. It is used to support an individual point load such as that due to a structural column. It may be circular, square or rectangular slab of uniform thickness. We use square shape footing for pad foundation.

Material Reinforced concrete

Type of excavation needed Pits

Number of stories can be construct Three to four stories

Structural type of the element

Fig 03: strip foundation

solid

RAFT FOUNDATION

We use raft foundation for large loads (e.g. 6 to 10stories). It is a large slab supporting a number of columns and walls under the entire structure or a large part of the structure.It is required when the allowable soil pressure is low or where the columns and walls are so close that individual footings would overlap or nearly touch each other.

Material Reinforced concrete

Type of excavation needed Bulk

Number of stories can be construct Six to seven stories

Structural type of the element Plate element

FLAT SLAB RAFT FOUNDATIONThis type of raft consist a solid slab of reinforced concrete. It is recommended for building areas subject to mining subsidence is similar to the flat slab, but cast on a bed of fine granular material 150 thick so that the raft is not keyed to the ground and is therefore unaffected by horizontal ground strains.

Fig 04: pad foundation

Fig 05: flat slab raft foundation

WIDE TOE RAFT FOUNDATION

It recommended for the area, where the ground has poor compressibility. Here we use beams to spread the column loads over the raft.

Fig 06: wide toe raft foundation

DEEP FOUNDATIONSWhen the soil at or near the ground surface is not capable of supporting a structure, deep foundations are required to transfer the loads to deeper strata.

PILE FOUNDATIONPile foundation as series of columns constructed or inserted into the ground to transmit the loads of a structure to a lower level of subsoil. Also piles define as a long vertical load transferring element.

Piles are relatively long, slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. They are used when for economic, constructional or soil condition considerations it is desirable to transmit loads to strata beyond the practical reach of shallow foundations. In addition to supporting structures, piles are also used to anchor structures against uplift forces and to assist structures in resisting lateral and overturning forces.

Piers are foundations for carrying a heavy structural load which is constructed insitu in a deep excavation.

Caissons are a form of deep foundation which are constructed above ground level, then sunk to the required level by excavating or dredging material from within the caisson.

Compensated foundations are deep foundations in which the relief of stress due to excavation is approximately balanced by the applied stress due to the foundation. The net stress applied is therefore very small. A compensated foundation normally comprises a deep basement.

End bearing piles

• Soft compressible soil• Hard incompressible layer

End bearing piles are those which terminate in hard, relatively impenetrable material such as rock or Fig 08: pile

Fig 07: pile

very dense sand and gravel. They derive most of their carrying capacity from the resistance of the stratum at the toe of the pile.

Friction piles

Soft soil becoming increasingly stiff with depth.

Friction piles obtain a greater part of their carrying capacity by skin friction or adhesion. This tends to occur when piles do not reach an impenetrable stratum but are driven for some distance into a penetrable soil. Their carrying capacity is derived partly from end bearing and partly from skin friction between the embedded surface of the soil and the surrounding soil.

Settlement reducing piles

Settlement reducing piles are usually incorporated beneath the central part of a raft foundation in order to reduce differential settlement to an acceptable level. Such piles act to reinforce the soil beneath the raft and help to prevent dishing of the raft in the centre.

Tension piles

Structures such as tall chimneys, transmission towers and jetties can be subject to large overturning moments and so piles are often used to resist the resulting uplift forces at the foundations. In such cases the resulting forces are transmitted to the soil along the embedded length of the pile. The resisting force can be increased in the case of bored piles by under-reaming. In the design of tension piles the effect of radial contraction of the pile must be taken into account as this can cause about a 10% - 20% reduction in shaft resistance.

Laterally loaded piles

Almost all piled foundations are subjected to at least some degree of horizontal loading. The magnitude of the loads in relation to the applied vertical axial loading will generally be small and no additional design calculations will normally be necessary. However, in the case of wharves and jetties carrying the impact forces of berthing ships, piled foundations to bridge piers, trestles to overhead cranes, tall chimneys and retaining walls, the horizontal component is relatively large and may prove critical in design. Traditionally piles have been installed at an angle to the vertical in such cases, providing sufficient horizontal resistance by virtue of the component of axial capacity of the pile which acts horizontally. However the capacity of a vertical pile to resist loads applied normally to the axis, although significantly smaller than the axial capacity of that pile, may be

Fig 10: tension pile

Fig 09: friction pile

fig11: wintch machine

sufficient to avoid the need for such 'raking' or 'battered' piles which are more expensive to install. When designing piles to take lateral forces it is therefore important to take this into account.

Piles in fill

Recent fill

Consolidating soil

Hard incompressible layer

Piles that pass through layers of moderately- to

poorly-compacted fill will be affected by negative skin friction, which produces a downward drag along the pile shaft and therefore an additional load on the pile. This occurs as the fill consolidates under its own weight.

CLASSIFICATION OF PILES

Based on material used Steel piles Concrete piles Timber piles Composite piles

Based on mode of transfer loads En- bearing piles Friction piles Combined end bearing and friction piles

Based on method of installation Driven piles pile

driven machine Bored and cast-in-piles Screw piles Jacked piles

Why “SUVA” construction selected the ‘RAFT’ foundation?

Strip foundation and pad foundation are not suitable for this building. Because

fig10:

They are most suitable only for light load structure, but this building is a seven storey building

So, more suitable for selected building is raft foundation, because of the following reason, More economical than pile foundation It makes Less pollution to environment than pile foundation Some what easy to construct It reduces the differential settlement on non- homogeneous soil

Fig 12: position of raft foundation

Construction process of the raft foundation

To answer this task, I selected the ongoing site which is situated in bambalapitiya. It is a seven storied building and it is one of the construction site of ‘SUVA’ properties.

Do the bulk excavation to up to 3 m. Compact the excavated area well Do the formwork for raft beam. Place the screed concrete. (Grade-15 concrete to 75 mm thickness) Apply a Damp proof membrane, here we used bitumote carpet Place the motor screed to 25 mm thickness (to cover D.P.M.) Do the reinforcement arrangements for raft beam

Place the cover blocks according to BS 8110 table 2.4 &table 2.5, between formworks and reinforcement arrangements.

Set the column position and arrange the reinforcement for column. Pour the Grade-25 concrete into formwork to a thickness of 800 mm and compact well by poker

vibrator. After 24 hours start the curing and cure it continuously at least for 7 days. After the curing process, lay the kicker to set out the alignments of column. Keep the kicker surface

roughly by scrapping. Do the rendering of 25mm thickness to receive the floor finishes

Task 2.2

The types of excavation carried out at the selected site.

The ten storey building of ‘SUVA properties’ is a raft foundation. Therefore the Bulk excavation is the best method of excavation for this.

First of all they selected the appropriate excavation method for the proposed foundation• Here, the proposed foundation was raft, because of that they selected the bulk excavation

Plan the work • They planed to do the excavation and construction part by part, Because of it is somewhat easy.

Site clearance• They removed the un wanted trees, bushes and tree roots on the surface

Identify and mark the boundary line of the area to be excavated• They identified the position through the proper surveying using theodalite and chain surveying.

Start the excavation• They started the excavation using GCB excavator.

Shoring• While, they excavate they did they proper shoring to the land.( shoring is briefly discussed on the

shoring ) Do the dewatering process continuously Disposal of the shoring material

• While they excavated, they did the disposal activity.

At the site:

First of all they have cleaned the site. It makes them to precede the work easier. After that bulk excavation was done. In this excavation ground was excavated up to 2m, with the use of

back co.

Temporary supporting system

Fig No: - 16 (Temporary supporting system)

There are three types of shoring. They are,

Cantilever shoring: - The cantilever method relies entirely on the passive resistance of the soil below the excavation line to support the excavation active load and live loads. The cantilever method is the simplest from a construction standpoint.

Box shoring: - The box system relies entirely on the internal bracing to resist the excavation active and live load forces. This shoring system can often be designed to be very efficient structurally.

Braced shoring: - The braced system uses internal bracing and the embedded pile to share the support of the excavation active pressure and surcharge loads.

After finishing the borehole test according to that at the site contractor used raft foundation. Before placing the foundation they have to prepare the site and have to do some arrangements.

According to the site before placing the foundation they have work according to some steps.

Method of construction of the foundation Clearing the site: - As foundations, drainage works, septic tanks, pit-type, latrines and soak pits of the

old building were cleaned. Grass, small trees, hills, hillock and bushes etc were removed inside of the

land. Underground electric or telephone cables as drainage or water supply lines were again checked.

Setting out: - After the site clearance and according to the structural designers design the building structure was marked in the land.

Bulk excavation: - According to the raft foundation bulk excavation was done at the site with the use of backhoes and dig up to 2M depth.

Disposal of excavation materials: - With the use of trucks from the site materials are disposed at the site. Compaction: - After disposing the materials excavated land was compacted with some vibrator

machines (Vibrating Rammer).

Fig No: - 18 (Vibrating hammer)

Dam proof course: - Before placing the concrete in the vibrated land dam proof course was done. For this BARRA LASTIC material was used at the site.

Formwork: - At this time form work was done for temporary use. And it was done with the use of plywood’s.

Screed concrete: - Concrete was put for the basement of the vibrated land. Reinforce arrangement: - After the concreting work reinforcement arrangement was done. According to

the borehole result raft foundation was used at the site. So reinforcement arrangement also done for raft foundation.

After arranging the reinforcement concreting work was done by the use of plumbing method. After placing the concrete after seven days, concrete work was cured by the use of some gunny bags.

Note: - It is necessary to keep the concrete structure wet, after they have lay and to protect them against the weathering action of atmosphere. The chemical process of gradual hardening taken placed in the presence of water for a very long time. But the process of hardening takes place rapidly in early days after the concrete has been laid and gradually slows down.

Task 2.3

Describe the construction method of foundation

In this storey building method of the construction of the raft foundation are given below:

Site Clearing:

As foundations, drainage works, septic tanks, pit-type, latrines and soak pits of the old building

were cleaned.

Grass, small trees, hills, hillock and bushes etc were removed inside of the land.

Underground electric or telephone cables as drainage or water supply lines were again checked.

Enclosing the Sites:

Purpose:

Protect from illegal activities by the unauthorized persons.

Public should not be affected – Ex. Falls into a pit trench.

Protection from material theft`

Layout: Created boundary line of the plan of the building by ropes and pegs.

Soil Investigation: Bore hole test; soil analysis by soil report.

Setting Out a Framed Building

Excavation: (bulk excavation)

Measured land for the foundation.

Plank shoring was fitted.

Procedure in final excavations for the foundation.

Filling around the building.

Excavated earth was Disposed or reused.

Excavated area was levelled.

Already depicted our site excavation and its temporary works, supporting system under the TASK-

5.

Foundation:

1” (25mm) rig foam and polythene were applied form foundation to roof to separate the

existing building.

Lean concrete was applied for 3”

Reinforcement arrangement for 1’(used stools and cover blocks), (clear cover to

reinforcement 11/2” )

Then, concrete was applied (mortar 1:2:4)

Levelling, setting, vibrating, and compressing to concrete.

Curing.

Conclusion

In this task it includes the various types of foundations; these details are taken from the books and internet. I got sufficient knowledge in this foundation types.

Raft foundation is selected for our site. It is a eight storey building and the soil is average soil. In raft foundation we can change the necessary area. Raft foundation cost is low than pile foundation cost. For this reason we selected raft foundation.

Before starting the foundation work we need the excavation work. In this task various types of excavation

methods were classified and we select bulk excavation for our site.

in this task briefly described about the method of construction of the raft foundation.

The foundation of a building is one of the most important elements of a building. It is the lowest part of a structure below the ground level, which is direct contact with soil. Provided to transmit the loads on the structure including the dead weight of the structure itself to the soil below

A foundation is a system which transfers the load of a structure, safely into the ground.

. The provision of foundation is made in such a way that the soil below the foundation is not stressed beyond its safe allowable bearing capacity. Depending upon the type of soil existing at site, its safe bearing capacity and the type of building, which is required to be constructed, a structure may need shallow or deep foundation. It is often misunderstood that the foundation is provided to support the load of the structure. In fact, it is a device to transmit the load of the structure to the soil below. Foundation is provided for the following four main purposes:-

To distribute the weight of the structure over large area to avoid over-loading of the soil beneath.

To load the sub-stratum evenly and thus prevents unequal settlement.

To provide a level surface for building operations.

To take the structure deep into the ground. Thus increase its stability, preventing overturning.

Cause of failure of foundation

Unequal settlement of the sub-soil.

Unequal settlement of masonry.

Horizontal movement of the soil adjoining the structure.

Shrinkage due to withdrawal of moisture from the soil below the foundation.

Lateral pressure tending to over turn the structure.

Action of atmosphere.

SUPERSTRUCTURE

SUB STRUCTURE

FOUNDATION

Fig 3.1

DIFFERENT TYPES OF FOUNDATIONS

There are mainly two types of foundations

Shallow Foundations Deep Foundations

SHALLO FOUNDATION

When the foundation is placed near to the finished ground surface, known as shallow foundation.

There are various types of shallow foundations, but three main shallow foundations are,

Pad foundations Strip foundations Raft foundations

Pad foundation

Pad foundations are used to support an individual point load such as that due to a structural column. They may be circular, square or rectangular. They usually consist of a block or slab of uniform thickness, but they may be stepped or hunched if they are required to spread the load from a heavy column. Pad foundations are usually shallow, but deep pad foundations can also be used.

Fig 3.2

Strip foundations

Wide stripe foundation Deep stripe foundation

Strip foundations: Strip foundations are used to support a line of loads, either due to a load-bearing wall, or if a line of columns need supporting where column positions are so close that individual pad foundations would be inappropriate.

Fig 3.3

SRIP FOUNDATION

Fig 3.5

Fig 3.4

STRIP FOOTING DETAILS

Fig 3.6

Strip foundation

Analysis

This foundation is little used for my selected area. This foundation is usually used for single storey building. This foundation excavation method is cheap and simple. But in my selected site construction is 6 storey building. So in my selected site this foundation is not suitable.

Raft foundation

Fig 3.7 Raft foundation

Flat raft Wide toe raft

Raft foundations are used to spread the load from a structure over a large area, normally the entire area of the structure. They are used when column loads or other structural loads are close together and individual pad foundations would interact.

A raft foundation normally consists of a concrete slab which extends over the entire loaded area. It may be stiffened by ribs or beams incorporated into the foundation. Raft foundations have the advantage of reducing differential settlements as the concrete slab resists differential movements between loading positions.

Fig 3.8

RAFT FOUNTING DETAILS

DEEP FOUNDATIONS

In case of bearing capacity of the soil is very poor and depending on some other conditions, the structure has to be taken deep into the soil, it is termed as deep foundation.

There are mainly two types of deep foundations

Pile foundations

Caisson foundations

Analysis

In my selected site consider bearing capacity of soil, ground water level, sub soil condition, Storey of building and cost, suitable foundations are raft and pile. We can put pile foundation it’s very strong but that is very expensive. So in my selected site most suitable foundation is raft.

Pile Foundations

Pile foundations are the part of a structure used to carry and transfer the load of the structure to the bearing ground located at some depth below ground surface.

There are two basic types of piles,

End bearing piles

Friction piles

End bearing piles

End bearing piles are those which terminate in hard, relatively impenetrable material such as rock or very dense sand and gravel. They derive most of their carrying capacity from the resistance of the stratum at the toe of the pile.

Friction piles

Friction piles obtain a greater part of their carrying capacity by skin friction or adhesion this tends to occur when piles do not reach an impenetrable stratum but are driven for some distance into a penetrable soil. Their carrying capacity is derived partly from end bearing and partly from skin friction between the embedded surface of the soil and the surrounding soil.

Fig 3.9

Caisson Foundation

Caissons are a form of deep foundation which are constructed above ground level, then sunk to the required level by excavating or dredging material from within the caisson.

CAISSON FOUNDATION

Fig 01 3.10

At our site used pile foundation. They consider followings

Load of the building

Soil bearing capacity

Water table level

Near place

Conclusion

I have studied the types of foundation. After testing the soil a report will be submitted by the testing company before deciding which type of foundation should be done we must consider the soil report the carry. In my selected site raft foundation placed so I got knowledge about raft foundation.

TASK-4

Identify and discuss various factors considered in selecting a foundation type and justify the selected type of foundation for the building selected.

Selecting a suitable foundation

We should consider the following condition when we choose the correct type of foundation

The load bearing capability of the ground The depth where we will find the suitable load bearing soil The distance from trees which can affect the stability of the soil The level of the the water table The normal variation in the water table The total weight of the building The strength of the natural foundation

The vibration and noise effects are very high. Vibration is not very much effect to the house.

Because,

We have to care about noise insulations.

Proposed building closed to the seaside.That reason,

The soil layer is very loose and not much strength. So the bearing capacity of soil is very low.

Water table level is very high. So we can’t build depth foundations.

Sea area has “sodium chlorides” it may be effect on steel structures.(cohesion)

Its close to a single story building.

That reason we have to care about very much.

Because,

If the foundation is very depth it’s may be affected from existing building’s foundation. Some times it’s may be collapse.

There for we have to concern shoring methods.

When we compact the soil we have to use vibrates. It’s also going to be effect the existing building. Some times

partitions can be crakes.

Those reason I suggest most suitable foundation is raft foundation.

Because,

Raft foundations are can build soft clay, marshy site having low rule of bearing capacity, heavy concreted structural loads

are generally supported by providing raft foundation. Also if the structure is liable to subsidence on account of its being

located in mining area or due to uncertain behavior of its subsoil water condition raft foundation should be preferred.

It’s provides an economical solutions to difficult site conditions, where pile foundation can not be used advantageously

and independent column footing becomes impracticable.

Raft foundation consist tie reinforcements concrete slab covering entire area of the bottom of the

structure like the floor. The slab is reinforced with bars running at right right angle to each other both near bottom

&top face on slab. Some times it’s necessary carry the excessive column load by an arrangement of inverted main

beams. cast monolithically with the raft slab.

RECOMMENDATIONS FOR FOUNDATION

It is recommened that draft foundation shall be used for the proposed 6 storyed building

Excavation shall be done up to a depth of about 2m at each foundation location The founcation could be placed at this depth and the allowable bearing pressure can be taken taken as 200 kN/ m2

Fig 4.1 Section view of Raft foundation.

Fig 4.2Plan view of Raft foundation

TASK-5

Describe the method of excavation and the associated temporary work carried out at your site.

Excavation

Removing soil or spoil from a predetermined area by manually or machine is called excavation.

WHAT IS AN EXCAVATION ?

An Excavation is any man-made or a machinery cut, cavity, trench, or depression in an earth surface that is formed by earth removal.

EXCAVATION

Fig 5.1

TYPES OF EXCAVATIONS

There are several types of excavation used in the building process, the type and method depending on the amount of ground to be excavated. There are five common excavations,

Soil strip Reduced-level excavation Bulk excavation Trench excavation

Hole or pit excavation

Soil strip

Unless the work is being carried out in a redevelopment area, the first section of ground should be excavated is the top soil or vegetable soil. This procedure knows as soil strip excavation.

Reduced-level excavation

The ground which lies between the topsoil and the earth’s crust known as the subsoil. And comprises particles of weathered rock of various shapes and size. It is usually necessary to provide a level surface from which construction may take place, and this level may be lower than the top of the subsoil. In such case, excavation into the subsoil is required to reduce the level of

the ground. The volume of subsoil to be excavated, together with the nature of the material, will determine the type of machine and methods to be used.

Fig 5.2

REDUCED-LEVEL EXCAVATION

Bulk excavation

Where large volumes of subsoil are required to be excavated in order to reach the formation level, the excavation is known as bulk excavation. This type of excavation may be to reduce levels or to provide basement areas. In addition to the plant already mentioned, a face shovel may so be used for this type of work.

Trench excavation

Having excavated or filled to a formation level, it is frequently necessary to excavate trenches to a lower level. In these trenches the foundations of the building are constructed. Trenches are also required outside the building for the laying of pipes and cables which carry gas, water, electricity, and other services.

Fig 5.3

TRANCH EXCAVATION

Hole or pit excavation

The design of the substructure may require holes or pits to be excavated. In the case of circular holes, hand or mechanically driven auger or drills are used. Pits, being small shallow or rectangular holes, may be excavated mechanically or by hand.

WHAT IS A TEMPORARY WORK ?

Temporary work is, during the construction works going on, need various types of temporary supports, unless we carried out at our site during the construction, may be will have to face to many risks. (Ex: workers safety problems, collapsing etc...)

TYPES OF COLLAPSE

To prevent from these kind of collapses, in construction using a temporary work known as shoring,

Shoring is the provision of a support system for trench faces used to prevent movement of soil, underground utilities, roadways, and foundations. Shoring or shielding is used when the location

or depth of the cut makes sloping back to the maximum allowable slope impractical. Shoring systems consist of posts, wales, struts, and sheeting.

There are three basic types of shoring,

Timber Hydraulic Pneumatic

Timber shoring

Fig 5.4

TIMBER SHORING

Hydraulic shoring

The trend today is toward the use of hydraulic shoring, a prefabricated strut and/or wale system manufactured of aluminum or steel.

Hydraulic shoring provides a critical safety advantage over timber shoring because workers do not have to enter the trench to install or remove hydraulic shoring.

Other advantages of most hydraulic systems are that they,

Are light enough to be installed by one worker;

Are gauge-regulated to ensure even distribution of pressure along the trench line;

Can have their trench faces "preloaded" to use the soil's natural cohesion to prevent movement; and

Can be adapted easily to various trench depths and widths.

All shoring should be installed from the top down and removed from bottom up.

Hydraulic shoring should be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and any other damaged or defective parts.

Fig 5.5

TYPES OF HYDRAULIC SHORIN G

Fig 5.6

Pneumatic shoring

Pneumatic shoring works in a manner similar to hydraulic shoring. The primary difference is that pneumatic shoring uses air pressure in place of hydraulic pressure. A disadvantage to the use of pneumatic shoring is that an air compressor must be on site.

Screw Jacks. Screw jack systems differ from hydraulic and pneumatic systems in that the struts of a screw jack system must be adjusted manually. This creates a hazard because the worker is required to be in the trench in order to adjust the strut. In addition, uniform "preloading" cannot be achieved with screw jacks, and their weight creates handling difficulties.

Single-Cylinder Hydraulic Shores. Shores of this type are generally used in a water system, as an assist to timber shoring systems, and in shallow trenches where face stability is required.

Underpinning. This process involves stabilizing adjacent structures, foundations, and other intrusions that may have an impact on the excavation. As the term indicates, underpinning is a procedure in which the foundation is physically reinforced. Underpinning should be conducted only under the direction and with the approval of a registered professional engineer

TYPES OF SCREW JACKS

Fig 5.7

TASK-6

Identify and state the method of construction of the foundation selected for your building.

Construction Steps for the Foundation

Program schedule for site works arrangements.

The client’s architect arrange for feasibility site for its purpose. That carried out by the contractor for the purpose of preparing tender. The topography of the site and outline planning Site security services electricity, transport, telephone, water supply services Sanitary drainage facilities Labor, Equipments and vehicles availability. Safety storage facilities

Setting out

Proposed building area lines will be checked. Excavation area will be marked. All the grid lines will be marked

Excavation work

Excavation method Deep of the excavation Machineries Earth disposal Shoring arrangements

Dewatering

If dewatering work is required, dewatering arrangements. Pumps or well points arrangements. The dewatered water should be removed continuously from that area

Form work arrangement

Arrange form work for foundation Shoring arrangements

Reinforcement

Make steel bar arrangement and binding Make column bar arrangement from foundation

Water proofing

Waterproofing materials Surface application Material mixing with concrete

Concreting

Materials

Mixing Placement of concrete Testing Finishing Curing of concrete

Curing

After the drying period we should arrange some curing arrangements.

Curing should do continuously for particular period.

2.1 Introduction

The type of foundations are decided according to the load of the building, bearing capacity of the soil. When a site with the good bearing capacity of reasonable depth is available it is not difficult to decide on the type of foundation. The purposes of the soil investigation are follows,

To get details the seasonal volume changes in the soil

To find out the bearing capacity of the sub soil

To ascertain the possibility of ground movement

To predict the likely behavior of the sub soil under seasonal and ground water level changes.

To determine the nature of the sub soil

2.2 Classification of Soil

Rocks – these include igneous rock (e.g. granite), sedimentary rocks (e.g. limestone and sandstone) and

metamorphic rocks

Cohesive soils – these include clays where the fine grained particles are closely integrated and stick

together

Non-cohesive soils – these include gravels and sand whose strength is largely depends on the grading and

closeness of the course-grained particles.

Peat – which is decayed vegetable matter of low strength with a high moisture and acidic content?

Made grounds – containing waste of one kind or another.

Soil can be classified by its partial or grain size as

- Gravel or Sand,

- Silt and

- Clay.

The size distribution of soil particles are established by means of sieving and sedimentation.

However, many soils are formed a combination of particles from the main soil groups and this

classification can be illustrated using a triangle called soil classification triangle.

2.3 Methods of soil investigation

Numerous methods can be used to conclude the soil conditions. following methods are dedicated With larger building or more difficult sites,

Trial pits- Relatively cheap and easy method of obtaining soil data by enabling easy visual inspection of the soil strata in its natural condition. The pits can be hand or machine excavated to a plan size of 1.2×1.2 and spaced at centre’s to suit the scope of investigation.

Boreholes- Boring uses a bit with chisel point screwed to a steel rod. These enable disturbed or undisturbed samples to be removed for analysis and testing but undisturbed samples are sometimes difficult to obtain from soils other than rocks or cohesive soils. Disturbed samples can be obtained by using a flight auger or percussion boring in a similar manner to the formation of small diameter bored piles using a tripod or shear leg rig.

Load testing- Such as by applying a compressive load on a platform which exerts a recorded pressure on a steel plate between 300 and 1000 mm diameter placed on the surface of the bottom of a trial pit. (Grundy,1998)

2.4 Summary of the borehole investigation

using the result of bore hole investigation, a profile of the sub surface conditions at the location of the borehole has been constructed.

Borehole results indicate that

1) The ground water level (G.W.L.)is lying at a depth of around 3.4m from the surface

2) The soils above GWL consist of 0.5m of lateritic fill followed by a fine clayey sand

3) Lying immediately beneath GWL is a very dense layer of fine to coarse and this extends up to a depth of 11.7m.

4) A thin intrusion of highly consolidated peat is present at 11.7m depth

5) The residual formation is encountered at a depth of 12.4 m this consists in situ weathered products of the parent rock lying beneath the bore hole was terminated within this layer at a depth of 15.5m.

Table No-1 The sub-surface at BH-01 has been modeled as indicated belowI.

Layer No Position(m) Layer description AverageSPT

01 0-0.5 Reddish brownLateritic soil (fill)

5

02 0.5-4.5 BrownishVery fine to fine Clayey sand

_

03 4.5-7.5 yellowish Very fine to fine Clayey sand

>50

04 7.5-10 yellowish Very fine to coarseClayey sand

>50

05 10-11.7 Pinkish yellowFine to coarse sand

>50

06 11.7-12.4 Blackish peat _

07

08

12.4-15.00

15.00-15.45

Grayish to yellowish white fine to coarse sandy clay

YellowishVery highly weathered rock

11

36

SPT- (Standard Penetration Test).

2.5 Conclusion

According the soil investigation raft foundation is most suitable than other foundation because bearing capacity of the soil is low , Water table level is 3.4 m, total load of the building is high. When the excavation time dewatering system should be used . Excavation can be continued up to 3.6 m. Most area of the site is sand so suitable shoring method must be used.

Task-3

Describe different types of foundations

3.1 Introduction

The foundation of a building is that part of the substructure which is in direct contact with and safely transmits loads to the suitable subsoil. The substructure is that part of a building or structure which is below natural or artificial ground level and which supports the super structure.

The choice and design of foundations depends mainly the following factors should be considered.

The total load of the building The nature and bearing capacity of the subsoil Water table level Economical factors Availability of materials Availability of services. Natural hazards

Task-4

Identify and discuss various factors considered in selecting a foundation type and justify the selected type of foundation for the building selected

4.1 Factors considered in selecting a foundation type

Apartment building which was selected ours have seven storied building and soil structure having low bearing capacity, So foundation should have more strength and shear force. So pile and raft foundations are suitable for this site.

When it was compared with other foundation types. strip or pad foundations are very low strength foundations. These types of foundations are commonly used for single storey or double storey buildings. But, if soil structure is good. then only these types of foundations can put for 3or 4 storey buildings.

Strip, pad and raft foundation cannot carry heavy loads when pile foundation is most suitable

when it was conceded pile foundation; this foundation is suitable for our site and strength also high. But if pile foundation is used, more space and more equipments are needed. But this site has small area. If Pile foundation is used, the cost is also high. So that pile foundation is not suitable for this site. So they have selected raft foundation in our building site.

Table No-2 Comparison of Raft and pile foundation.

factor Raft Pile

1)Low bearing sub soils Suitable Suitable

2)Multi store building Suitable Suitable

3) Cost of construction Low high

4)Special machineries and skilled laborers

No need need

5)Affect the adjoin building during the excavation

little Very high

6)Going deep for foundation No need need

7)More working space No need need

So, raft foundation is the most suitable for this kind of building. As, Raft is most suitable for medium dense sand Suitable for this filled area

When it was considered these factors, raft foundation is most suitable for this construction.

4.2 Justification

The Raft foundation and Pile foundation have evaluated by me .which is suitable for selected building by ours but Raft foundation is most suitable for selected building. More Justifications for the selection of Raft foundation have been described below

The most influence cause is the type of soil, total load of the building, and water table level. In Galle road frontage area the bearing capacity of the soil is very low (annex -1)and in this context there is a water table level is encountered of the ground level also building is resided near the road and beside the sea the vibration would caused, should be considered and wind load also considered because of these reasons Raft foundation is most suitable than other foundation.

Task-5

Describe the method of excavation and the associated temporary work carried out at your site

5.1 Introduction

Excavation method is most important part of the construction work. When we start before the foundation we have to dig the soil from ground level. This process called as excavation.

5.2 Method of excavation

Fig no - 09- types of excavation

Excavations may be classified as shallow, medium and deep.

1. Shallow – 1.5m deep

2. Medium – 1.5 to 3.0 m deep

3. Deep – over 3 m deep

Foundation and its suitable excavation are given below

Pad foundation - Trench and Pit excavation

Strip foundation – Trench and Pit excavation

Raft foundation – Bulk excavation

Pile foundation - Hole excavation

Trench excavation

Having excavated or filled to a formation level, it is frequently necessary to excavate trenches to a lower level. In these trenches the foundations of the building are constructed. Trenches are also required outside the building for the laying of pipes and cables which carry gas, water, electricity, and other services(Chudley, 1979, pp. 10-15)

Discussion

seven storey building visited by ours so, this excavation is not suitable foundation.

Evaluation

When considering this site, the type of sub soil, The ground water level most suitable excavation is Bulk excavation .Because our site suitable foundation method is raft.

When we considering above these factors, raft foundation is most suitable for this construction , this apartment have7 story building and soil structure having very low bearing capacity, so the soil structure should bear 7 story building load , so foundation should have more strength and shear force . That’s why raft foundation is most suitable. So, suitable excavation method is Bulk.

We can’t do strip and pad foundation because those are very less strength foundations. These are used to small story buildings. That’s why we can’t do Trench and Pit excavation.

We can’t use pile foundation excavation. Because when we use the pile foundation we need more space and more machinery facilities. But these sites have small area. Pile foundation provides high cost. So we can’t use Hole excavation. Excavation method is correct and suitable for this site.

5.3 Temporary works

5.3.1 Shoring

This is a method temporarily supporting system of structures or sides of excavation by shores

Fig no-10 Shoring systems

Dead shoring

This type of shoring is used to support dead loads which act vertically downwards. In its simplest form it consists of a vertical prop or shore leg with a head plate, sole plate and some means of adjustment for tightening and easing the shore. The arrangement is to use two shore legs connected over their heads by a horizontal beam or needle. The loads are transferred by the needle to the shore legs and hence down to a solid bearing surface. (Chudly.R 1979)

Fig no.11 Dead shoring

Raking shoring

This shore transfers the floor and loads to the ground by means of sloping struts or rakers. Rake’s angle should be between 400 and 700 with the horizontal. The centre line of the raker should intersect with the centre lines of the wall

Fig no.12 Raking shoring

Fly shoring

These shores fulfill the same functions as a raking shore but have the advantage of providing a clear working space under the shoring. They can be used between any parallel wall surfaces providing the span is not in excess of 12.000 m when the arrangement would become uneconomic. Short spans up to 9.000 m usually have a single horizontal member whereas the large span require two horizontal shores (Chudly, 1979)

Fig no.13 flying shoring

Evaluation

There are different types of shoring methods are available. But this selected site most suitable shoring method is flying shore. We consider Flying or horizontal shores this is not exceeded 12m. But our site span is lesser than 12m. So we can do this method. We consider dead shores this method carried out only vertical loads. So, this method also not suitable in my site.

Considering all things in visited site the most suitable method is flying shore.

Horizontal Vertical and horizontal load

5.3.2 Dewatering

Fig no.14

Dewatering systems

WellPoint systems - Popular method for water lowering in non-cohesive soils up to a depth of between 5 and 6. To dewater an area beyond this depth requires a multi-stage installation .The basic principle is to water jet into the ground a number of small diameter wells which are connected to a header pipe which is attached to a vacuum pump. WellPoint systems can be installed with header pipe acting as a ring main enclosing the area to be excavated. The header pipe should be connected to two pumps, the first for actual pumping operation and second as a standby pump since is essential to keep the system fully operational to avoid collapse of the excavation should a pump failure occur. The alternative system is the progressive line arrangement where the header pipe is placed alongside a trench or similar excavation to one side or both sides according to the width of the excavation. (Chudly, 1977)

Sump pumping - suitable for most soils and in particular gravels and coarse sands when working in open shallow excavations. It’s limited to a maximum depth of 7.5 m.

Shallow well system

A shallow well system, a hole of about 30cm diameter is bored into the ground, using a casing. A filter tube of about 15cm diameter, covered with a special wire mesh. This system is used very rarely.

Deep well system

A deep well is about 30 to 60 cm in diameter, bored to a depth of 15 to 30m The spacing of deep wells between 10 to 30 m. In this system pumping once started must be continued until entire excavation work is completed

Evaluation

We can use this method for bulk excavation. When comparing other dewatering methods, this method is very economical and easy. There are some pumps available in this method. In my site dewatering selection is correct. Considering all factors in this site dewatering method is good.

According to the geotechnical investigation, dewatering should be done. This site that have raft foundation so excavation area is large because well point system was used.

5.4 Conclusion

Bulk excavation & WellPoint dewatering system are suitable to visited site

Task-6

Identify and state the method of construction of the foundation selected for your site

6.1 Introduction

A seven storey apartment building, which was located in bambalappitia was considered by ours to gathering information for our assignment work. Residence structural engineer Mr. D.T.Rajasekeran. was discussed by ours about the procedures of constructing the foundation work because the selected site foundation work had been finished one year ago. Therefore he was explained about that particular foundation which they used (RAFT) and method of its construction. I was able to get the required knowledge and information from our visiting site.

6.2 Method of construction of the foundation

Plan

We should plan the building’s layout properly and decide on the specification for each major item of work so that the cost of construction can be kept within the estimated value.

Man power – skilled, semi skilled and unskilled Materials – cement, sand, metal, steel etc Construction shed – warehouse for materials, office and workers accommodation Utilities Wastages – what to do with excavated soil & other wastages Fore seeing – problems to be faced and possible sudden problems such as heavy rain, accident, storm

may arise Controlling man power and material with related to time, economy and efficiency

Site Clearing

Surface cleaning such as grass, trees, hillock etc Obstructions cleaning above or below the ground such as old drainage, old foundation, soak pit

Enclosing the site

Layout

Creating a boundary line by using robes and pegs

Soil Investigation - Borehole, soil test reports

Type of excavation can be found from the soil investigation report

Setting out

Before the excavation of trenches for foundation, the setting out is done in the site.

Setting out of centre line Setting out of trenches Level out the formation level Compact the formation level by vibrator If it is very loose soil it should be removed and back filled with good soil

If the water table is higher than the formation level then the dewatering should be carried out Lay polythene sheet in overlapping way for water proofing to protect the foundation from dampness Pour screed concrete Grade 20 was used Cement : Sand : Coarse Aggregate = 1 : 3 : 6 After 24 hours, curing should be carried out for 7 days According to the structural design of foundation, reinforcement was arranged Set out the column position and reinforcement for column starter bar Reinforcement for staircase if needed Covering for reinforcement Set out form work and check the form work Pour the concrete for foundation If it is mixed mechanically the standard cement sand ration can be 1:1.5 If it is mixed by manually 10% of cement should be added to the concrete more than the cement mixed

mechanically Sufficient compaction should be carried out Curing for 14 days

Then after remove frame work and make arrangements for column work

Objective of foundation

Foundation is provided for the following purpose;

6. To distribute the load of structure, on large area, so that the intensity of load does not exceed the safe bearing capacity of the underlying soil.

7. To distribute the load on underlying soil evenly and thus to prevent unequal settlement of the foundation.

8. To provide a level and hard surface for the super structure to be build over it.

9. To increase the stability of the structure as a hole, against sliding, overturning or other disturbing forces like wind, rain etc.

10.To prevent lateral movement of the supporting material, so that the safetyof the structure is not endangered.

Essential requirements of a good foundation

Foundations should be constructed to satisfy the following requirements

1. The foundations shall be constructed to sustain the dead and imposed loads and transmit these to the sub soil in such a way that pressure on it will not cause settlement which would impair the stability of the building or adjoining structures.

2. Foundation base should be rigid so that differential settlements are minimized, specially for the case when super imposed loads are not evenly distributed.

3. Foundations should be taken sufficiently deep to guard the building against damaged or distress caused by swelling or shrinkage of the sub soil.

4. Foundations should be so located that its performance may not be affected due to any unexpected future influence.

Design and choice of a foundation

1. The following factors to be considered in choice and design of a foundation,

2. The bearing capacity of subsoil and its nature

a. The maximum allowable load per unit area is called as bearing capacity. It is depend on

b. Type of soil

c. Density, shearing strength and other physical properties of soil

d. Water table level

3. Structural load of building

4. Construction cost

5. Speed of construction

6. Weather conditions

7. Physical properties of foundation(Size, Shape, Type)

8. Depth below ground level

9. Continuation of soil strata

10.Construction problems

11.The factor that ratio of Load / Bearing capacity of soil

12.Shearing stress and Vertical pressure

Selection of most suitable foundation

Pile foundation is not suitable for this building. For the following reasons

There will be more skilled laborers needed. Also huge machineries widely needed. Erecting piles may cause damages on the surrounding buildings. And pay compensation

for them. All these above will increase the overall cost of construction. All clients expect low cost

construction. As; pile foundation is not suitable for this dwelling.

Also, pad foundation is not suitable for this building. For the following reasons

It’s not suitable for filled areas. In this case around half of this land is covered by peat soil. It is removed and refilled. So, pad is not suitable.

This land has silty clay soil type. It is a very loose soil. For silty clay it is not suitable. So, raft foundation is the most suitable for this kind of building. For the following reasons

Raft is most suitable for silty clay type soil. Suitable for this filled area Sometimes columns may be closely spaced. More economical than pile foundation Safe than pile foundation for environment.

Task-2.2 Describe the method of excavation and the associated temporary work carried out at your site.

We have to do excavation for some of reasons mentioned below,

To remove unsuitable material such as peat, black cotton soil and other filled materials. To level the uneven ground. To achieve the required level. To construct the superstructure. To construct the underground structure like basement.

There are two types of excavation methods

Manual Machinery

The selection of excavation method depends on the following factors

Nature of the sub soil Purpose of the excavation Presence of the ground water Availability of the plant and the site limitation Location of the excavation Cost

We can categorize the excavation in three categories, by considering the deep of the excavation.

Shallow - Up to 1.5 m deep. Medium – 1.5 m to 3 m deep Deep – above 3 m deep

Types of excavation

There are several types of excavation used in the building process, the type and method depending on the amount of ground to be excavated.

Soil strip Reduced level excavation Bulk excavation Trench excavation Hole or Pit excavation

Soil strip

After vegetable soil is removed excavation is takes place. The process is to strip the surface of the ground of its topsoil covering, and this may be achieved by the use of certain types of machinery bulldozer pushing the topsoil layer to a convenient stockpile position a short distance away;(Figure:07)

subsoil

cuting cuting

filling

fromation level

By a scraper ‘paring off’ the top layer, transporting it, and depositing it at a stockpile position some distance away on large site

By a drag line scraping of the top layer and either depositing it at convenient stockpile or loading the material into wagons for transport off site

By back actor operating in a similar manner to the drag line

By the mechanical shovel (track- or wheel – driven) operating in a similar manner to the drag line

By a skimmer – a machine specifically designed for this type of work

(Figure:07)

Reduced level excavation

The ground which lies between the topsoil and earth’s crust is known as the subsoil ands comprises particles of weathered rock of various shapes and sizes. It is usually necessary to provide a level surface from which construction may take place, and this level may be lower than the top of the subsoil. In such cases, excavation into the subsoil is required to reduce the level of the ground. The volume of subsoil to be excavated, together with the nature of the material, will determine the type of machine and methods to be used.(Figure:08)

On sloping site it may be necessary to cut in to the banking on one side of the proposed building, while filling with suitable material on the other side, in order to achieve the level working surface or formation level.

(Figure:08)

Bulk excavation

vertical of straight faces

pier holes

Where large volumes of subsoil are required to be excavated in order to reach the formation level, the excavation is known as bulk excavation. This type of excavation may be reduce levels or to provide basement areas. In addition to the plant already mentioned, a face shovel my also be used for this type of work.

Trench excavation

Having excavated or filled to a formation level, it is frequently necessary to excavate trenches to a lower level. In these trenches the foundations of the building are constructed. Trenches are also required outside the building for the laying of pipes and other services.(Figure:09)

(Figure:09)

Hole or pit excavation

The design of the substructure may require holes or pits to be excavated. In the case of circular holes, hand mechanically driven augers or drills are used. Pits, being small shallow or rectangular holes, may be excavated mechanically or by hand.(Figure:10)

(Figure:10)

The method of excavation carried out at the selected site.

I selected the site which is situated at No.32, Dharmarama road, Colombo-06. It is a seven storied apartment building.

Bulk excavation

First of all they selected the appropriate excavation method for the proposed foundation

• Here, the proposed foundation was raft, because of that they selected the bulk

excavation

Plan the work

• They planed to do the excavation and construction part by part, Because of it is some

what easy.

Site clearance

• They removed the un wanted trees, bushes and tree roots on the surface

Identify and mark the boundary line of the area to be excavated

• They identified the position through the proper surveying using theodalite and chain

surveying.

Start the excavation

• They started the excavation using JCB excavator.

Shoring

• While, they excavate they did they proper shoring to the land.( shoring is briefly

discussed on the shoring )

Dewatering process was carried out continuously

Disposal of the shoring material

• While they excavated, they did the disposal activity.

Task-2.3 The method of construction of the foundation selected for your building.

Construction of raft foundation

Large area of this construction site is filled area. Extra beam edges are put in filled area or loose soil area to spread the column load.

So, in this case the beam and slab raft is most suitable. Generally the raft slab is laid for a depth of 300mm to 450mm. The slab should be laid for

450mm to avoid failure. The beam edge depth is 450mm. The overall depth of raft foundation below the existing ground floor is 900mm.

The excavation is done as per requirement and well consolidated. This surface when dry provide the reinforcement arrangements for raft beam, raft slab and column base upon where the raft is laid.

The following figure: 11 show the typical reinforcement arrangement of raft foundation.

Reinforcement arrangement of raft foundation

(Figure:11)

(Figure:11)-

Position of reinforcements of raft foundation.

Construction process of foundation and column footing

Do the formwork and reinforcement arrangements for raft beam. Before do the formwork, place the mass concrete as blinding layer of 50mm thickness over the

1000 gauge polythine (DPM). Place the cover blocks between formworks and reinforcement arrangements. Also, setout the column position and arrange the reinforcement for column. Pour the concrete into formwork depth of 450mm and compact by pocker vibrator. Normally

Grade 25 concrete can be used. After 24 hours striking the form work and start the curing and continue it at least 7 days. After 14 days the raft beams get strong. Then fill the good soil up to beam level and mechanically compact it thoroughly layer by layer. Place the mass concrete as a thin blinding layer over the polythine(DPM). (Place the DPM in

remaining part) Then fabricate the reinforcement net for raft slab and lay it over the cover blocks. Do the formworks for other remaining parts. Place the concrete for raft slab in depth of 450mm and after 24 hours cure it continuously 7

days. After the curing process, lay the kicker to set out the alignments of column. Keep the kicker

surface roughly by scrapping. Make formworks to continue the column construction. Keep cover blocks between formworks

and reinforcement arrangements. Place Grade 25 concrete for a depth of more than 300mm. its maximum height 4’ to 5’, to

avoid the segregation of coarse aggregates. Compact it by pocker vibrator. After 24 hours striking the formworks and cures it by tying the wetted gunny bags around the

column. Then fill with good imported soil upto the proposed ground level around depth of 300mm. Before the filling do the water proofing for column up to proposed ground level. Compact the filled soil mechanically and layer by layer. Place the mass concr ete as a thin layer over the DPM and fabricate the reinforcement net by

using 10mm Tor steel and place it over the concrete layer. The cover blocks are kept between reinforcement net and concrete layer. Place the concrete

(G25) up to depth of 75mm to100mm.

Do the rendering of 25mm thickness to receive the floor finishes.

spread foundation

Shallo

strip

combined

pad

combined f mat

deep

caisson f

pile f