Introduction to Soil Mechanics Lecture.pdf

8/12/2019 Introduction to Soil Mechanics Lecture.pdf

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Technological University of the Philippines

Ayala Blvd. Ermita, Manila

College of Engineering

Department of Civil Engineering

CE 4104A

Soil Mechanics

Assignment No. 1

Introduction to Soil Mechanics

Fesalbon, Mayson R.

10-205-041

June 25, 2013

Engr. Jesus Ray M. Mansayon

Instructor


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Soil Mechanics Geotechnical Engineering Foundation Engineering

Soi l Mechanics

In general, Soil Mechanicsis the branch of science that deals

with the study of the physical properties of soil and the

behaviour of soil masses subjected to various types of forces.

[1]Karl Terzaghi, the father of modern soil mechanics

[2],

defined soil mechanics as follows:

Soil Mechanics is the application of the laws of

mechanics and hydraulics to engineering problems dealing

with sediments and other unconsolidated accumulations of

solid particles produced by the mechanical and chemical

disintegration of rocks regardless of whether or not they

contain an admixture of organic constituents.[3]

It differs from fluid mechanics in the sense that soils consist of a heterogeneous mixture of fluids

(usually air and water) and particles (usuallyclay,silt, sand, andgravel)but soil may also contain

organic solids, liquids, and gasses and other matter. Soil mechanics is used to analyse the

deformations of and flow of fluids within natural and man-made structures that are supported on

or made of soil, or structures that are buried in soils.[4]

The term Soil Mechanicsis now accepted

quite generally to designate the discipline of engineering science which deals with the properties

and behaviour of soil as a structural material.

[3]

Our main objective in the study of soil mechanics is to lay down certain principles, theories and

procedures for the design of a safe and sound structure.[3]

Geotechnic al Engineering

Geotechnical engineeringis the sub-discipline of civil engineering that involves natural materials

found close to the surface of the earth. It includes the application of the principles of soil

mechanics and rock mechanics to the design of foundations, retaining structures and earth

structures.[1]

It requires knowledge of strength and stiffness of soils and rocks, methods of

analyses of structures and hydraulics of groundwater flow.[5]

Foundat ion Engineer ing

Foundation engineering is an engineering field of study that deals to the design of those

structures which support other structures like buildings, bridges or transportation infrastructures

under different soil and environment conditions. It is at the periphery

ofCivil,Structural andGeotechnical Engineering disciplines and has distinct focus on soil-

structure interaction.[3][6]

Karl Terzagh i (1883 - 1963)

Source:http://benriya.files.wordpress.com/

2008/10/terzagi.jpg?w=198&h=300
http://en.wikipedia.org/wiki/Clayhttp://en.wikipedia.org/wiki/Gravelhttp://en.wikipedia.org/wiki/Civil_Engineeringhttp://en.wikipedia.org/wiki/Structural_Engineeringhttp://en.wikipedia.org/wiki/Geotechnical_Engineeringhttp://benriya.files.wordpress.com/2008/10/terzagi.jpg?w=198&h=300http://benriya.files.wordpress.com/2008/10/terzagi.jpg?w=198&h=300http://benriya.files.wordpress.com/2008/10/terzagi.jpg?w=198&h=300http://benriya.files.wordpress.com/2008/10/terzagi.jpg?w=198&h=300http://benriya.files.wordpress.com/2008/10/terzagi.jpg?w=198&h=300http://en.wikipedia.org/wiki/Geotechnical_Engineeringhttp://en.wikipedia.org/wiki/Structural_Engineeringhttp://en.wikipedia.org/wiki/Civil_Engineeringhttp://en.wikipedia.org/wiki/Gravelhttp://en.wikipedia.org/wiki/Clay


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Major Periods of Geotechnical Engineering[7]

The record of a persons first use of soil as a construction material is lo st in antiquity. For years,

the art of geotechnical engineering was based on only past experiences through successive

experimentation without any scientific character. Based on experimentations, many structures

were builtsome of which have crumbled while others are still standing.

Date Event

2750 B.C.The five most important pyramids (Saqqarah, medium, Dashmur South andNorth and Cheops) were built in Egypt.

2000 B.C.Dykes were built in the basin of the Indus to protect the town of MohenjoDara (Pakistan)

1120 B.C. to 249 B.C. Dykes were built in China during the Chan dynasty for irrigation purposes.

68 A.D. Thousands of pagodas were built in China during the Eastern Han dynasty.

1173 A.D. The construction of the Leaning Tower of Pisa in Italy began.

12th

Century The Garisenda Tower was built in Bologna, Italy.

The Leaning Tower of Pisa weighs about 15,600

metric tons and is supported by a circular basehaving a diameter of 20 m. The tower has tilted in

the past to the east, north, west and finally to the

south. Investigations showed that the weak clay

layer exist a depth about 11m below the ground

surface compression which caused the tower to tilt.

It was closed in1990 because of it was feared to

collapse with more than 5m out of plumb.

It has been stabilized by excavating soil from under

the north side of the tower. About 70 metric tons of

earth was removed in 41 separate extractions thatspanned the width of the tower.

Leaning Tow er of Pisa

Source:

http://4.bp.blogspot.com/-

3ijUwVQcmN0/UNAShgdfUBI/AAAAAAAAf88

/FtYVvmFciEw/s1600/Super+Goof+Pisa.jpg
http://4.bp.blogspot.com/-3ijUwVQcmN0/UNAShgdfUBI/AAAAAAAAf88/FtYVvmFciEw/s1600/Super+Goof+Pisa.jpghttp://4.bp.blogspot.com/-3ijUwVQcmN0/UNAShgdfUBI/AAAAAAAAf88/FtYVvmFciEw/s1600/Super+Goof+Pisa.jpghttp://4.bp.blogspot.com/-3ijUwVQcmN0/UNAShgdfUBI/AAAAAAAAf88/FtYVvmFciEw/s1600/Super+Goof+Pisa.jpghttp://4.bp.blogspot.com/-3ijUwVQcmN0/UNAShgdfUBI/AAAAAAAAf88/FtYVvmFciEw/s1600/Super+Goof+Pisa.jpghttp://4.bp.blogspot.com/-3ijUwVQcmN0/UNAShgdfUBI/AAAAAAAAf88/FtYVvmFciEw/s1600/Super+Goof+Pisa.jpghttp://4.bp.blogspot.com/-3ijUwVQcmN0/UNAShgdfUBI/AAAAAAAAf88/FtYVvmFciEw/s1600/Super+Goof+Pisa.jpghttp://4.bp.blogspot.com/-3ijUwVQcmN0/UNAShgdfUBI/AAAAAAAAf88/FtYVvmFciEw/s1600/Super+Goof+Pisa.jpg


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Pre-classic al Period of Soi l Mechanics (1700 to 1766 A.D.)

This period concentrated on the studies relating the natural slope and unit weights of various

types of soil.

Henri Gautier (1660 - 1737). Henri Gautier is a French royal engineer who studied in

1717 the natural slopes of soil when tipped in a heap for formulating the designprocedures of retaining walls. According to the study, the following results were obtained:

Classification of SoilNaturalSlope

Unit Weight

kN/m3

lb/ft3

Clean Dry Sand 31 18.1 115

Ordinary Earth 45 13.4 85

Bernard Forest de Belidor (1671 - 1761).He published a textbook for military and civilengineers in France. In his book, he proposed a theory of lateral earth pressure on

retaining walls as a follow-up on Gautiers original study. He also specified a soil

classification system shown in the table below.

Francois Gadroy (1705 - 1759). A French engineer who reported the first laboratory

model test results on a 76-mm-high retaining wall built with sand backfill in 1746. He also

observed the existence of slip planes in the soil at failure.

Classical Period of Soi l MechanicsPhas e I (1776 to 1856)

Charles Augustin Coulomb (1736 - 1806).A French scientist who presented a report

using the principles of maxima and minima to determine the true position of the sliding

surface in soil behind a retaining wall in 1776. He also used the laws of friction and

cohesion for solid bodies.

ClassificationUnit Weight

kN/m

lb/ft

Rock - -

Firm or hard sand 16.7 to 106 to

Compressible Sand 18.4 117

Ordinary earth (found in dry locations) 13.4 85

Soft earth (primarily silt) 16.0 102

Clay 18.9 120

Peat - -


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Jacques Frederic Francais (1775 - 1833) & Claude Louis Marie Henri Navier (1785 -

1836).Their study is related to inclined backfills and backfills supporting surcharge.

Jean Victor Poncelet (1788 - 1867). An army engineer and professor of mechanics

provides a graphical method for determining the magnitude of lateral earth pressure on

vertical and inclined retaining walls with arbitrarily broken polygonal ground surfaces. Hewas also the first to use the Greek letter Phi for soil friction angle. He also provided the

first ultimate-bearing capacity theory for shallow foundations.

Alexandre Collins (1808 - 1890).In 1846, he provides the details for deep ships in clay

slopes, cutting and embankments. He also observed that the actual failure surfaces could

be approximated as arcs and cycloids.

William John Macquorn Rankine (1820 - 1872). In 1852, he published a study on

theory on earth pressure and equilibrium of earth masses that ends the Phase I of

classical soil mechanics.

Classical Period of Soi l Mechanics Phas e II (1856 to 1910)

Henri Philibert Gaspard Darcy (1803 - 1858).A French engineer who published a study

on the permeability of sand filters in 1856. He defined the term coefficient ofpermeability

or hydraulic conductivityof soil.

Sir George Howard Darwin (1845 - 1912). A professor in astronomy who conducted

laboratory tests to determine the overturning moment on a hinged wall retaining sand in

loose and dense state of compaction.

Joseph Valentin Boussinesq (1842 - 1929).He published a development of the theory

of stress distribution under loaded bearing areas in a homogenous, semi-infinite, elastic

and isotropic medium in 1885.

Osborne Reynolds (1842 - 1912). He demonstrated the phenomenon of dilatency of

sand in 1887.

Mod ern Soi l Mechanic s (1910 to 1927)

Albert Mauritz Attenberg (1848 - 1916). A Swedish chemist and soil scientist who

defined clay-size fractionsas a percentage by weight of particles smaller than 2 microns

in size in 1908. In 1911, he explained the consistency of cohesive soils by defining liquid,

plastic and shrinkage limits. He also defined the plasticity index as the difference

between liquid limit and plastic limit.


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Jean Fontard (1884 - 1962). A French engineer who carried out an investigation to

determine the cause of failure of the 17-m high earth dam in Charmes, France that

happened on October 1909. He conducted undrained double shear test on clay

specimens (0.77 m2& 200 mm thick) under constant vertical stress to determine shear

strength parameters.

Arthur Langley Bell (1874 - 1956). A civil engineer who worked in the design and

construction of the outer sea wall at Rosyth Dockyard. He developed relationships for

lateral pressure and resistance in clay as well as bearing capacity of shallow foundations

in clay. He also used shear-box test to measure the undrained shear strength of

undisturbed clay specimens.

Wolmar Fellenius (1876 - 1957).An engineer from Sweden who developed the stability

analysis of saturated clay slopes (= 0) with the assumption that the critical surface of

sliding is the arc of the circle.

Karl Terzaghi (1883 - 1963).An Austrian who developed the theory of consolidation for

clays. It was published in his book Erdbaumechanikin 1925.

SOIL Its Origin and Types

The term Soil comes with different meanings, depending on the general field in which it is

considered and used.[8]

To an Agr icu l tur is t :

Soil is the top thin layer of earth within which organic forces are predominant and which is

responsible for the support of plant life.[8]

To a Geolog is t :

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 rockirrespective of its hardness.[9]

To an ENGINEER:

Soil is the uncemented aggregate of mineral grains and decayed organic matter (solid

particles) with liquid and gas in the empty spaces between the solid particles.[1]

Soil includes all earth materials, organic and inorganic, occurring in the zone overlying

the earths crust.[8]

Soil is also defined as a natural aggregate of mineral grains, with or without organic

constituents, which can be separated by mechanical means such as agitation of water.[10]


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Origin of Soil

In general, soils are formed by weathering of rocks. The physical properties of soil are derived

primarily by the minerals that constitute the soil particles and, hence, the rock from which is

derived.[8]

From the knowledge that soils comes from the weathering of rocks, this section will discuss itsprocess of weathering and the rock cycle.

Weathering[9][10]

Weathering is a process of breaking down rocks by mechanical and chemical processes into

smaller pieces to form soil or loose particles at or near the Earths surface. There are two types of

weathering which are the mechanical weatheringand chemical weathering.

Mechanical Weathering. Mechanical weathering is a type of weathering where the

physical characteristics of a rock have been changed like change in size, shape, texture,

etc. It may be caused by the expansion and contraction of rocks from the continuous gainand loss of heat which results in ultimate disintegration. Other physical agents that help

disintegrate rocks are glacier ice, wind, running water in rivers and streams, and ocean

waves.

Chemical Weathering.Chemical weathering is a type of weathering in which the original

rock is transformed into new minerals by means of a chemical reaction. In this type of

weathering, water plays an important role by providing oxygen and mobility of moving

ions that will cause a chemical reaction. The rate of chemical weathering depends on

three factors: temperature, surface area of the rock exposed and availability of water or

natural acid.Thus, tropical environment experiences most severe chemical weathering.

Transportation of Weathering Products. The products of weathering may stay in the same

place or may be moved to other places by different causes. The soils formed by the weathered

products at their place of origin are called residual soils.An important characteristic of residual

soil is the gradation of particle size. Fine grained soil is found at the surface, and the grain size

increases with depth. At greater depth, angular rock fragments may also be found. Transported

soil may be classified according to their mode of transportation and deposition.

1. Glacial soilsformed by the transportation and deposition of glaciers

2. Alluvial soilstransported by running water and deposited along streams

3. Lacustrine soilsformed by deposition in quiet lakes4. Marine soilsformed and deposited by the wind

5. Aeolian soilstransported and deposited by the wind

6. Colluvial soilsformed by the movement of soil by gravity


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Types of Soil

Acco rd ing to the i r Part ic le Size[14]

Soils generally are called gravel, sand, silt or clay, depending on the predominant size of particles

within the soil. Several organizations developed particle-size classification of soil.

Name of OrganizationGrain Size (mm)

Gravel Sand Silt Clay

Massachusetts Institute ofTechnology (MIT)

>2 2 to 0.06 0.06 to 0.002 2 2 to 0.05 0.05 to 0.002


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Acco rd ing to the i r Or ig in[15]

On the basis of origin of their constituents, soils can be divided into two large groups:

Residual Soils. Residual soilsare those that remain at the place of their formation as a

result of the weathering of parent rocks. The depth of residual soils depends primarily on

climatic conditions and the time of exposure. Its sizes of grains are indefinite.

Transported Soils.Transported soilsare soils that are found at locations far removed

from their place of formation. The agents of transport of these soils are the same as the

modes of transportation of the weathering products as discussed earlier on the topic

about weathering.

Soils that are generally used in practice[15]

Bento i te is a clay formed by the decomposition of volcanic ash with a high content ofmontmorillonite. It exhibits the properties of clay to an extreme degree.

Varved Claysconsist of thin alternating layers of silt and fat clays of glacial origin. They possess

the undesirable properties of both silt and clay.

Kaol in, China Clayis very pure forms of white clay used in ceramic industry.

Bou lder Clayis a mixture of an unstratified sediment deposit of glacial clay, containing unsorted

rock fragments of all sizes ranging from boulders, cobbles and gravel to finely pulverize clay

material.

Calcareous Soi lis a soil containing calcium carbonate. Such soil effervesces when tested with

weak hydrochloric acid.

Marlconsists if a mixture of calcareous sands, clays or loam.

Hardpanis a relatively hard, densely cemented soil layer, like rock which does not soften when

wet.

Caliche is an admixture of clay, sand and gravel cemented by calcium carbonated depositedfrom ground water.

Peat is a fibrous aggregate of finer fragments of decayed vegetable matter. It is very

compressible and should be cautious when using it for supporting foundations of structures.

Loamis a mixture of sand, silt and clay.


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Shaleis a material in the state of transition from clay to slate. When exposed to air or to take in

water, it rapidly decomposes.

ROCKS Its Origin and Cycle

Rockcan be defined as a compact, semi-hard to hard mass of natural material composed of one

or more minerals. The rocks are encountered at the surface of the earth or beneath and are

commonly classified into three groups according to their modes of origin: igneous, sedimentary

and metamorphic rockswhich are also inter-correlated to each other by a cycle called the rock

cyc le.[8]

The Rock Cycle

Since soil came from weathered rocks, the rock cycle contributes a great part in the origin andformation of soil.

The Rock Cycle

Source: http://etap.org/demo/Earth_Science/es3/1003_rock_cycle.jpg
http://etap.org/demo/Earth_Science/es3/1003_rock_cycle.jpghttp://etap.org/demo/Earth_Science/es3/1003_rock_cycle.jpghttp://etap.org/demo/Earth_Science/es3/1003_rock_cycle.jpg


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Igneous Rocks. Igneous rocks are formed from the solidification of molten magma

ejected from within the earths mantle. After a volcanic eruption, some of the molten

magma cools on the surface of the earth. Sometimes magma ceases its mobility below

the earths surface and cools to form intrusive igneous rocks that are called plutons.[11]

There are two main classes of igneous rocks. They are the following:[8]

1. Extrus ivethese are igneous rocks that poured out at the atmosphere

2. In trus ivethese are igneous rocks that have been formed below the earths

surface.

Sedimentary Rocks. Sedimentary rocks are formed when the products of the

disintegration and decomposition of any rock type are transported, redeposited and partly

or fully consolidated or cemented into a new type of rock.[17]

Methamorphic Rocks. Methamorphic rocks are formed when an any type of rock

undergoes a process called metamorphism.[16]

Metamorphism is a process when a rock

undergoes a complete or incomplete crystallization by high temperature, high pressuresand/or high shearing stresses without melting the rock.

[16][17]

Application of Soil Mechanics

Soil mechanics is a discipline that applies principles from engineering mechanics to predict the

mechanical behaviour of soils. Every man-made structure needs foundations to support the

forces applied to it. Any structure that is built lies on the ultimate foundationthe earth.[18]

That is why we need to study the behaviour of the soil and its interaction with the structures we

are going to build to ensure the safety of the people who will use it.[18]

Civi l Engineering. One major field of application of soil mechanics is in the field of civil

engineering. Consider the suspension bridge shown on the next page. In the analysis of a

suspension bridge, the loads on the roadway that is suspended from two main cables by means

of vertical hangers transfer to the main cables. The forces acting on the main cables will pass

over a pair of towers that are anchored into a solid rock or concrete foundation at their ends.

[19]

Same principle will also be exhibited to other types of structures. The knowledge on the lateral

earth pressure, soil-bearing capacity and slope stability of soil mechanics will be very much

helpful in the construction of any structures.


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Envi ronmenta l Geotechnics. Soil mechanics plays a very important role in the design,

construction, operation and maintenance of new waste disposal and containment facilities; and in

the isolation of contaminated ground. The following must be considered in a landfill that requires

knowledge and application of soil mechanics: [20]

1. The landfill must be safe against several possible types of stability failure.

2. The landfill must be able to withstand earthquake shaking, without gross stability

failure, rupture of linear system or failure of leachate collection and removal system.

3. The foundation soils must be able of supporting the tailing embankment.

4. The dam must be stable under both static and seismic loading at different stages of

construction and after completion to maximum height.

5. Stability of slurry trenches during excavation

6. Stresses and deformation of the ground adjacent to the slurry trench and their

potential adverse effects on structures and facilities.

Geotechnical Engineering. Geotechnical engineering uses principles ofsoil

mechanics and mechanics to investigate subsurface conditions and materials; determine the

relevant physical/mechanical and chemical properties of these materials; evaluatestability of

natural slopes and man-made soil deposits; assess risks posed by site conditions;

designearthworks and structure foundations; and monitor site conditions, earthwork and

foundation construction.[21]

Golden Gate Br idge, San Francisco Bay

Source: http://teachers.egfi-k12.org/wp-content/uploads/2010/03/800px-GoldenGateBridge-001.jpg
http://en.wikipedia.org/wiki/Soil_mechanicshttp://en.wikipedia.org/wiki/Soil_mechanicshttp://en.wikipedia.org/wiki/Slope_stabilityhttp://en.wikipedia.org/wiki/Slope_stabilityhttp://en.wikipedia.org/wiki/Earthworks_(engineering)http://teachers.egfi-k12.org/wp-content/uploads/2010/03/800px-GoldenGateBridge-001.jpghttp://teachers.egfi-k12.org/wp-content/uploads/2010/03/800px-GoldenGateBridge-001.jpghttp://teachers.egfi-k12.org/wp-content/uploads/2010/03/800px-GoldenGateBridge-001.jpghttp://en.wikipedia.org/wiki/Earthworks_(engineering)http://en.wikipedia.org/wiki/Slope_stabilityhttp://en.wikipedia.org/wiki/Slope_stabilityhttp://en.wikipedia.org/wiki/Soil_mechanicshttp://en.wikipedia.org/wiki/Soil_mechanics


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Mining. There are many applications of unsaturated soil in the mining field. This include the

wetting up and drain down of initially dry surface waste rock dumps; the irrigation and drain down

of heap leach materials; drain down, desiccation and rewetting of mine tailings; dewatering of

mineral products such as coal; the strength and compressibility of stored mine wastes by way of

rehabilitation.[22]


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References:

[1] Das, B.M. (2010). Principles of Geotechnical Engineering, 7

th Edition, Cengage Learning,

pp.19-22

[2]Das, B.M. (2010). Principles of Geotechnical Engineering, 7

thEdition, Cengage Learning, p.10

[3] Murthy, V.N.S. Geotechnical Engineering: Principles and Practices of Soil Mechanics and

Foundation Engineering, Dhanpat Rai and Sons, p.24

[4]http://en.wikipedia.org/wiki/Soil_mechanics

[5]Atkinson, J. (2007). The Mechanics of Soils and Foundation, 2

ndEdition, Taylor and Francis

Group, p.3

[6]http://en.wikipedia.org/wiki/Foundation_engineering


thEdition, Cengage Learning, pp.1-

7



[9]http://www.eng.fsu.edu/~tawfiq/soilmech/lecture.html





[12] Das, B.M. (2010). Principles of Geotechnical Engineering, 7

th Edition, Cengage Learning,

pp.19-22

[13]http://www.engr.uconn.edu/~lanbo/CE240LectW012Rock2soil.pdf




Foundation Engineering, Dhanpat Rai and Sons, pp.29-30




Foundation Engineering, Dhanpat Rai and Sons, pp.27

[18]http://wiki.answers.com/Q/What_is_the_importance_of_soil_mechanics_in_civil_engineering

[19]Kassimali, A. (2010) Strucutral Analysis, 4


[20]

Mitchell, J.K. (1995). The Role of Soil Mechanics in Environmental Geotechnics, The 3rd

Spencer J. Buchanan Lecture, pp.2-5

[21]http://en.wikipedia.org/wiki/Geotechnical_engineering

[22]Williams, D.J. Some Mining Application of Unsaturated Soil Mechanics, pp.1-20
http://en.wikipedia.org/wiki/Soil_mechanicshttp://en.wikipedia.org/wiki/Soil_mechanicshttp://en.wikipedia.org/wiki/Foundation_engineeringhttp://en.wikipedia.org/wiki/Foundation_engineeringhttp://www.eng.fsu.edu/~tawfiq/soilmech/lecture.htmlhttp://www.eng.fsu.edu/~tawfiq/soilmech/lecture.htmlhttp://www.eng.fsu.edu/~tawfiq/soilmech/lecture.htmlhttp://www.engr.uconn.edu/~lanbo/CE240LectW012Rock2soil.pdfhttp://www.engr.uconn.edu/~lanbo/CE240LectW012Rock2soil.pdfhttp://wiki.answers.com/Q/What_is_the_importance_of_soil_mechanics_in_civil_engineeringhttp://wiki.answers.com/Q/What_is_the_importance_of_soil_mechanics_in_civil_engineeringhttp://en.wikipedia.org/wiki/Geotechnical_engineeringhttp://en.wikipedia.org/wiki/Geotechnical_engineeringhttp://en.wikipedia.org/wiki/Geotechnical_engineeringhttp://wiki.answers.com/Q/What_is_the_importance_of_soil_mechanics_in_civil_engineeringhttp://www.engr.uconn.edu/~lanbo/CE240LectW012Rock2soil.pdfhttp://www.eng.fsu.edu/~tawfiq/soilmech/lecture.htmlhttp://en.wikipedia.org/wiki/Foundation_engineeringhttp://en.wikipedia.org/wiki/Soil_mechanics

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