Chapter 1 - Introduction and Soil Formation

CHAPTER 1

INTRODUCTION AND SOIL FORMATION

1.0 INTRODUCTION

Almost every work of construction in CE is built on soil or rock.

In many instances these are also the raw materials of construction.

1.0 INTRODUCTION

The term soil has various meanings, depending upon the general field in which it is being considered.

1.0 INTRODUCTION

Meanings of

SOIL

Toa

PEDOLOGIST

Toa

GEOLOGIST

Toan

ENGINEER

1.0 INTRODUCTION

Soil is the substance existing on the Earth’s surface, which grows and develops plant life

To a PEDOLOGIST

1.0 INTRODUCTION

Soil is the material in the relative thin surface zone within which roots occur, and all the rest of the crust is grouped under the term ROCK irrespective of it sharpness.

To a GEOLOGIST

1.0 INTRODUCTION

• Soil is the un-aggregated or un-cemented deposits of mineral and/ or organic particles or fragments covering large portion of the Earth’s crust.

• The void space between the particles containing water and/ or air.

To an ENGINEER

1.0 INTRODUCTION

Soil means material that can be worked without

drilling or blasting

1.0 INTRODUCTION

SOIL MECHANICS is single of the youngest disciplines of CE involving the study of soil, its behaviour and application as an engineering material.

1.0 INTRODUCTION

The study of soil and rock materials is an important

part of a wider area of study.

Geotechnical Engineering.

1.0 INTRODUCTION

Rock Mechanics

(Rock Stability and Tunneling)

Soil Dynamics

(Dynamic Properties of Soils, Earthquake

Engineering, Machine Foundation)

Foundation Engineering

(Deep & Shallow Foundation)

Pavement Engineering

(Flexible & Rigid Pavement)

GEOTECHNICAL ENGINEERING

Geosynthetics

(Soil Improvement)Soil Mechanics

(Soil Properties and Behaviour)

2.0 SOIL FORMATION

SOIL

The un-cemented or weakly cemented material overlying the harder rock on the plane’s surface.

All soils originate, directly or indirectly from solid rocks and these are classified according to their mode of formation:

-Igneous rocks

-Sedimentary rocks

-Metamorphic rocks

2.0 SOIL FORMATION

IGNEOUS ROCKS

• Formed by cooling from hot molten material (magma) with or on the surface of the earth’s crust

• e.g., granite basalt, dolcrite, andesite, gabbro, syenite, porphyry.

SEDIMENTARY ROCKS

• Formed in layers from sediments settling in bodies of water, such as seas and lakes.

• e.g., limestone, sandstone, mudstone, shale, conlonerate.

METAMORPHIC ROCKS

• Formed by alternation of existing rocks due to extreme heat & extreme pressure.

• e.g., marble, quartzite, slate, schist.

2.0 SOIL FORMATION

CONTROLLING FACTORS OF SOIL

FORMATION

Nature and composition of the parent rock.

Climate conditions, particularly temperature and humidity.

Topographic and general terrain conditions, such as degree of shelter or exposure, density and type of vegetation, etc.

Length of time relate to particular prevailing conditions.

Interference by other agencies, e.g. cataclysmic storms, earthquakes, action of man etc.

Mode and condition of transport.

2.0 SOIL FORMATION

Igneous Rock

2.0 SOIL FORMATION

Igneous Rock

2.0 SOIL FORMATION

Metamorphic Rock

2.0 SOIL FORMATION

Metamorphic Rock

2.0 SOIL FORMATION

Sedimentary Rock

2.0 SOIL FORMATION

Sedimentary Rock

2.0 SOIL FORMATION

The geological process that produce soil

The effect of WEATHERING

The effect of TRANSPORT

2.1 THE EFFECT OF WEATHERING

The effect of WEATHERING

Weathering embraces a number of natural surface processes

which result from the single or combined action of such agencies as wind, frost,

temperature change and gravity.

Frost action, in which water within the pore spaces of a rock expands upon freezing causes flakes or rock to split away. The resultant debris is therefore sharp and angular.

Wind action, causes the particles to become rounded.


Wind action causes the particles to become rounded.


The volume change as liquid water transforms to ice is an important physical weathering force in temperate

climates.



2.2 THE EFFECT OF TRANSPORT

Soils that have not been transported and have

remained at their parent site are termed

RESIDUAL SOILS.


The principal effect of transportation is that of sorting. During the processes of movement, separation of the original constituents takes place.

In hot arid climates, e.g. a fine wind-blown dust known as LOESS may be carried considerable distances before being deposited.


•However, the velocity falls as the river drops down towards the sea, and so deposition takes place: first, gravel-sized particles are deposited in the flood plain and then coarse to medium sands, finally fine sands and silts in the estuary or delta area.

•Clay particles, because of their smallness of size and flaky shape, tend to be carried well out into the sea or lake.

•Thus, river-deposited (alluvial) soils are usually well sorted, i.e. poorly or uniformly graded.


•The action of flowing water may dissolve some minerals, carrying some particles in suspension and bounce or roll others along.•The load carried by a river or stream depend largely on the flow velocity.•In the upper reaches the velocity is high and so even large boulders maybe moved.



The movement of ice also provides transport for weathered debris e.g. boulder clay.

What type of soils are usually produced by

the different weathering and transportation

process?Boulders, gravel

cohesionless, sand and silt cohesive and

clay

These soils can be dry, saturated and partially saturated.

They have different shapes and

textures.

2.3 ENGINEERING SOIL TERMINOLOGY

ROCK

Hard rigid coherent deposit forming part of the earth’s crust, which may be of igneous, sedimentary or metamorphic origin.

To geologist, the term rock indicates coherent crustal material over about 1 million years old.

Soft materials such as clays, shales and sands, may be described by a geologist as rock, whereas an engineer will use the term soil.


SOIL

In engineering taken to be any loose or diggable material that is worked in, worked on or worked with.


ORGANIC SOIL

This is a mixture of mineral grains and organic material of mainly vegetable origin in varying stages of decomposition.


PEAT

True peat is made up entirely of organic matter, it is very spongy, highly compressible and combustible.

Inorganic materials may also be present and as this increased the material will grade towards an organic soil.

From an engineering point of view, peat poses many problems because of their high compressibility, void ration and moisture content, and in some case their acidity.


RESIDUAL SOILS

These are the weathered remains of rocks that have undergone no transportation.

They are normally sandy and gravelly.

E.g., China clay.


ALLIVIAL SOILS

(ALLUVIUM)These are materials, such as sands and gravels which have beeb deposited from rivers and streams.


COHESIVE SOIL

Soils containing sufficient clay or silt particles to impart significant plasticity and cohesion.


COHESIONLESS SOIL

Soils, such as sands and gravels, which consist of rounded and angular (non-flaky) particles and which do not exhibit plasticity or cohesion.


BOULDER CLAYThis is soil of glacial origin consisting of a very wide range of particle sizes from finely-ground rock flour to boulders.

SOIL MECHANICS (7 TOPICS)

1. Soil Formation• Formation

2. Soil Classification• Soil classification system

3. Physical Properties• Soil compositions and their relationships

4. Index Properties• Plastic, liquid and plasticity index

SOIL MECHANICS (7 TOPICS)

5. Moisture Density Relationships• Soil compaction

6. Flow of Water in Soils• Permeability and seepage

7. Stress Distribution• Effective stress and pore water pressure

LAB TESTS

1. Liquid Limit & Plastic Limit

Plastic LimitLiquid Limit

LAB TESTS

2. Sieve Analysis & Field Density

Sieve Analysis Field Density

LAB TESTS

3. Determination of Specific Gravity of Soil

LAB TESTS

4. Water Content Determination

Drying OvenCompaction Graph

By: fiza

Chapter 1 - Introduction and Soil Formation

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