Lecture 01 Soil Mechanics

7/27/2019 Lecture 01 Soil Mechanics

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By:

Engr. Imtiaz Ahmed



Introduction Soil Index Properties

Identification and Classification of Soil

Soil Compaction Permeability

Soil Exploration

Shear Strength

Earth Pressure

Stresses in Soil



INTRODUCTION &SOIL CHARATERICTICS



Soil is a natural body comprised of solids (minerals and organicmatter), liquid, and gases that occurs on the land surface,occupies space, and is characterized by one or both of thefollowing: horizons, or layers, that are distinguishable from theinitial material as a result of additions, losses, transfers, andtransformations of energy and matter or the ability to supportrooted plants in a natural environment.

Soil is formed over a long period of time.

The formation of soil happens over a very long period of time. It

can take 1000 years or more. Soil is formed from the weatheringof rocks and minerals. The surface rocks break down intosmaller pieces through a process of weathering and is thenmixed with moss and organic matter.



“Branch of engineering science which enable anengineer to know theoretically or experimentally thebehavior of soil under the action of loads (static ordynamic) and gravitational forces as well as underthe influence of water and temperature.”

A famous scientist, Terzaghi defines it as

“It is the application of laws of hydraulics and

mechanics to engineering problem dealing withsediments and other unconsolidated accumulationsof solid particles produced by the mechanical andchemical disintegration of rocks”



A typical geotechnical engineering project beginswith a site investigation of soil, rock, faultdistribution and bedrock properties on and belowan area of interest to determine their engineeringproperties including how they will interact with, on

or in a proposed construction. Site investigationsare needed to gain an understanding of the area inor on which the engineering will take place.Investigations can include the assessment of therisk to humans, property and the environment fromnatural hazards such as earthquakes, landslides,sinkholes, soil liquefaction, debris flows and rockfalls.



Perform soil surveys

Develop soil sampling device and methods

Develop soil testing device and methods Determine physical properties of soil

Adoption of soil conservation techniques

Adoption of most suitable methods to control

sedimentation of dam reservoirs Select suitable sites for disposal of wastes



Weathering is the process of the breaking down rocks. There are twodifferent types of weathering. Physical weathering and chemicalweathering. In physical weathering it breaks down the rocks, butwhat it's made of stays the same. In chemical weathering it stillbreaks down the rocks, but it may change what it's made of. Forinstance, a hard material may change to a soft material after

chemical weathering.

STAGE 1 STAGE 2 STAGE 3

STAGE 4



Following are the typical types of soil

Glacial

Residual Alluvial

Aeolian (Wind Blown)

1. Dune or Dune Sand

2. Loess



Glacial Soil:

Developed, transported and deposited by theaction of glaciers. Consists of rock fragment,

boulder, gravel, sand, silt and clay

Residual Soil:

Found on nearly flat rock surfaces whereweathering action produces a soil. Occurswhen weathering is higher than removal



Alluvial:

Transported and deposited by water.

Aeolian:

Transported and subsequently deposited by

wind

1. Dune:

Characterized by low hill and ridge formation

2. Loess:

Wind blown dust (siliceous silt or silty-clay)laid down in a loose condition



Dunes Loess



Clay: very fine particles less than .002 mm insize. Flaky in shape, considerable surfacearea

Silt: Between .002 and .06 mm in size. Hashigh capillarity, no plasticity and little drystrength

Sand: Between .06 and 2 mm in size. Roundto angular in shape. No plasticity, highpermeability and low capillarity.



Gravel: Between 2 to 60mm. Good foundationmaterial. When mixed sand and silt, bearingcapacity is increased.

Cobblers or Boulders: larger than gravel. 60to 200mm. Larger than 200mm are Boulders.

Organic Matter: source is plants or animalremains. Top 12” of soil have organic matter.



Physical Properties Of Soil



Colour Structure Shape and Size Specific Gravity Phases Porosity Void Ratio Moisture Degree of Saturation



Wide variety in nature Depends upon type of soil, mineral matter,

organic contents and amount of coloringoxides

Black due to Manganese

Green or Blue= Ferrous

Red, Brown or Yellow= Iron

Grey= Organic Matter



PARTICLE BONDINGTHE PARTICLE BONDING IS VERY WEAK SO RELATIVELYEASY TO GOING TO CHANGE AND HAVE NON-LINEAR

BEHAVIOUR AND CHARACTERISTIC

SHAPE, SIZE AND STRUCTURE OF SOILPARTICLE



S : Solid Soil particleW: Liquid Water (electrolytes)

A: Air Air



Void ratio e (given in decimal, 0.65)

Porosity n (given in percent 100%, 65%)

)V(solidsof Volume)V(voidsof Volumee

s

v

)V(samplesoilof volumeTotal)V(voidsof Volumen

t

v

e1e

)e1(VeVn

s

s



WATER CONTENT ; : The ratio of the amount of water (Ww) in the

soil (Ws) and expressed as a percentage

0% < <

DEGREE OF SATURATION ; S : The ratio of water volume air (Vw) to

void volume (Vv) and expressed as a percentage

0% S 100%

%100 xW

W

s

w

%100 xV

V S

v

w



UNIT WEIGHT : The ratio of weight to volume

SPECIFIC GRAVITY ; GS : The ratio of unit weight of soil to unitweight of water

RELATIVE DENSITY ; Dr :

w

w

wV

W

s

s

sV

W

V

W

w

sGS

%100minmax

max x

ee

ee Dr

o



Standards◦ ASTM D854-92 Standard Test Method for Specific

Gravity of Soils

◦ ASTM C127-88 (Reapproved 1993) Test Methodsfor Specific Gravity and Absorption of CoarseAggregate.

◦

BS 1377: Part 2:1990

Lecture 01 Soil Mechanics

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