Advisor: Dr. Hema Siriwardanekti.mtu.edu.iq/lectures/area/zainab/SoilMechanics.pdf · Soil Mechanics Importance The study of the science of soil mechanics equips a civil engineer

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SOIL MECHANICS

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Adeyeri, Joseph B ,Technology and Practice in Geotechnical Engineering.

Das, B.M., Principle of Geotechnical Engineering 5th edition.

Braja M. Das 2000 ,Soil mechanics laboratory manual 6th ed.

R.F. Craig, Soil mechanics.

REFERENCES

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Grading

• Attendance, Class Participation and quizzes.

• Midterm Exam.

• Laboratory attendance, participation and experiments reports.

• Final Exam.

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Class Outline

•Origin of Soil, soil composition and index properties

• Weight-Volume Relationships, Plasticity and Structure of Soil

• Engineering Classification of Soil

•Permeability

•Fluid flow in soil

•In Situ Stresses (Effective Stress Concept)

•Stresses in a Soil Mass

•Compressibility of Soil

•Shear Strength of Soil

•Soil Compaction

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Soil Definitions

The term Soil has various meanings, depending upon the general field in which

it is being considered.

• Pedologist .... Soil is the substance existing on the earth's surface, which

grows and develops plant life.

• Geologist ..... 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 its hardness.

• Engineer .... 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.

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Soil Definitions

• Composition of soil particles depends on composition of parent rock.

• The void spaces between the particles contain water and/or air.

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Soil Formation

Soils may be formed in place from rock or formed in weathered rock and

minerals that have been transported from where the original rock occurred.

Physical disintegration

Chemical decomposition

Physical disintegration causes decrease in size without appreciably

altering composition. Differential stresses due to heating and cooling or

expansion of ice break the rock. Abrasion due to water containing

sediment or wind carrying debris is another type of physical weathering.

Chemical weathering of rocks

•Due to water, acids or alkaline

•Oxidation – union of oxygen with minerals in rocks forming another

minerals

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Types of Soil

Residual soil: the products of rock weathering

remain at their original location.

Transported soil: the products are transported and

deposited in a different location. (gravity, wind,

water).

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Soil Applications

Engineer uses the SOIL to build:

buildings, tunnels, and dams.

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Soil Mechanics

Soil Mechanics is one of the youngest disciplines of Civil Engineering involving the study

of soil, its behavior and application as an engineering material. Soil mechanics is the

science of equilibrium and motion of soil bodies. Here soil is understood to be the

weathered material in the upper layers of the earth’s crust

Soil mechanics has become a distinct and separate branch of engineering mechanics

because soils have a number of special properties, which distinguish the material from

other materials. Its development has also been stimulated, of course, by the wide range of

applications of soil engineering in civil engineering, as all structures require a sound

foundation and should transfer its loads to the soil.

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Soil Mechanics Importance

The study of the science of soil mechanics equips a civil engineer with the basis

scientific tools needed to understand soil behavior.

Every civil engineering structure, whether it is a building, a bridge, a tower, an

embankment, a road pavement, a tunnel or a dam, has to be founded on the soil

(assuming that a rock stratum is not available) and thus shall transmit the dead

and live loads to the soil stratum.

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The physical state of a soil sample

Soil may be divided into three main classes:

1.Coarse – grained or non-cohesive soil

2.Fine – cohesive soil

3.Organic soil

Coarse grain soil

Boulders > 300mm

Cobble 150-300mm

Gravel 2-150mm

Sand 0.06-2mm

Fine grain soil

Silt 0.002-0.06mm

Clay <0.002mm

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The physical state of a soil sample

• Soil is a three phase material, contain soil particles and voids. Voids are fill

with water and air.

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The physical state of a soil sample

Total Volume = Vt = Vs + Vw + Va

Total Weight = Wt = Ws + Ww

Porosity (n): is the ratio of void volume.

n = Vv/Vt

Void Ratio (e):is the ratio of void volume to solid volume.

e = Vv/Vs

now n = Vv/Vt = Vv/ Vv+ Vs = (Vv/Vs)+1

e=e+1

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States of Soil

Depending on the water content of the soil, it may appear in four states: solid,

semi-solid, plastic and liquid.

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Water Content

For many soils, the water content may be an extremely important index used

for establishing the relationship between the way a soil behaves and its

properties. The consistency of a fine-grained soil largely depends on its water

content. The water content is also used in expressing the phase relationships of

air, water, and solids in a given volume of soil.

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Water Content

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Water Content

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Water Content

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