CE 206CE 206 Geotechnical EngineeringGeotechnical Engineering --IICE 206 CE 206 Geotechnical Engineering Geotechnical Engineering II

Syllabus

Origin of soil, Phase relationships, Identification and classification of soils, Effective stress principle, , p p ,Permeability of soils, Compressibility of soils, Seepage and flownets, Terzaghi’s one-dimensional consolidation , gtheory, Shear strength of soils, Effective stress and total stress strength parameters, Total and effective stress g p ,paths, Compaction of soils.

Textbooks & References

G l R j d R A S R B i d A li d S il M h i N A Gopal Ranjan and Rao, A.S.R. Basic and Applied Soil Mechanics, New Age International, 2000.

Coduto, D. P., Yeung, M. C. and Kitch, W. A, Geotechnical engineering: principles and , , g, , , g g p ppractices, New Delhi : PHI, 2011

Kaniraj, S.R. Design Aids in Soil Mechanics & Foundation Engineering, Tata McGraw Hill 1988Hill, 1988.

Holtz, R. D. Kovacs, W. D. and Sheahan, T. C. An Introduction to Geotechnical Engineering, Second edition, Pearson, 2013.

Budhu, M. Soil Mechanics and Foundations, 2e, Wiley India Pvt. Ltd., 2008 Terzaghi, K., Peck R. B. and Mesri, G. Soil Mechanics in Engineering Practice, John

Wiley & Sons 1996Wiley & Sons, 1996. Lambe T.W. and Whitman, R.V. Soil Mechanics, John Wiley & Sons, 1969. Indian Standard Codes of Practice (IS 2720) ( )

Origin of SoilOrigin of Soil

CE 206CE 206 Geotechnical EngineeringGeotechnical Engineering IICE 206 CE 206 Geotechnical Engineering Geotechnical Engineering --IIDepartment of Civil Engineering

Indian Institute of Technology GuwahatiIndian Institute of Technology Guwahati

SoilSoil

Originated from the Latin word Solum Different meaning for Different Professions

Agriculturist The top thin layer of earth within which organic forces are

predominant and which is responsible for the support of plant life

Geologist The material in the top thin zone within which roots occur.p

Engineer soil includes all earth materials organic and inorganic occurring in soil includes all earth materials, organic and inorganic, occurring in

the zone overlying the rock crustSoil is defined as the uncemented aggregate of mineral grains Soil is defined as the uncemented agg egate of mine al g s

and decayed organic matter (solid particles) with liquid and gas in the empty spaces between the solid particles

Soil formationSoil formation

Soils are formed by weathering of rocks Size of the individual grains varies over a wide range Physical properties of soil Physical properties of soil

Dictated by size, shape and chemical composition primarily by the minerals hat constituted the soil particles i e the primarily by the minerals hat constituted the soil particles i.e the

rock from which it is derived

So knowledge on types of rocks and weathering process So knowledge on types of rocks and weathering process

WeatheringWeathering

The process of breaking down rocks by physical (mechanical), chemical and biological processes into smaller pieces

Physical or Mechanical weathering By physical processy p y p Impact, grinding and erosive action of water, ice and wind

Opening of cracks as a result of unloading due to the erosion ofOpening of cracks as a result of unloading due to the erosion of overlying soil and rock

Retain minerals of parent rockp

Chemical weathering Oxidation hydration carbonation leaching by organic acids of Oxidation, hydration, carbonation, leaching by organic acids of

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Different Rock TypesDifferent Rock Types

Based on the mode of origin 3 types Igneous Rocks

formed by the solidification of the molten magma ejected from deep within the earth's mantlethe earth s mantle

Depending on type of minerals present in magma and rate of cooling different types of igneous rocks are formed

Sedimentary Rock Soil deposits transformed back into rocks through hardening process

Clastic rocks Carbonates

Metamorphic Rock Metamorphic Rock Metamorphisum the process of changing the composition and

texture of rocks without melting by heat and pressuretexture of rocks, without melting, by heat and pressure

Rock cyclesRock cycles

The final productsdue to weathering aredue to weathering aresoils

(Das, 1998)

Composition of some Igneous Rocks (Das 2006)Composition of some Igneous Rocks (Das, 2006)

Rock MineralsRock Minerals

Feldspar Quartz Ferromagnesian minerals Ferromagnesian minerals Iron oxides

C l i Calcite Dolomite Mica Gypsum Gypsum

SoilsSoils

Residual soils Rock weathering products located at the place where they

originated Not common

Transported soilsp Transported from the place of origin By wind, water, ice or any other agencyy , , y g y

Characteristics of soil such as size of particles their shape, roundness, surface texture and degree of sorting areroundness, surface texture and degree of sorting are influenced by agency of transportation

Residual soilsResidual soils

When rock weathering process is faster than the transport process

Retains many of the characteristics of the parent rocky p Tropical regions

Very thick residual soils (~ 100s of meters) over unweathered Very thick residual soils ( 100s of meters) over unweathered rock Called Literites – cemented with iron oxides having high dry strengthg g y g

Cooler and more arid regions Much thinner layers (may be no residual soil) Much thinner layers (may be no residual soil)

Soil type depends on parent rock D p d it d id l il Decomposed granite- sandy residual soil Shale type sedimentary rock - clayey residual soils

Different soils based on depositionDifferent soils based on deposition

Alluvial Deposits From suspension of running water

Lacustrine Depositsp Suspensions in still and fresh water of lakes

Marine Deposits Marine Deposits Sea water suspensions

A li D it Aeolian Deposits Transported by wind

Glacial Deposits Transported by ice

Effects of Transportation on Sediments (L b & Whit 1969)Effects of Transportation on Sediments (Lambe & Whitman 1969)

Alluvial SoilsAlluvial Soils

Transported to their present position by rivers or streams Very common Contains extensive ground water aquifers Contains extensive ground water aquifers When flow is rapid

Sil d l i i i Silts and clays remain in suspension Only sands, gravels, and boulders deposited

f f If flow is slow More of finer soils also deposited

Alluvial soils often contain alternating horizontal layers of different soil types Formation of different soils during different seasons due to

different flow rates

Alluvial fans Deposits formed at the foot of a canyon Common in arid regions

In steep terrains Large boulders are carried by waterLarge boulders are carried by water Subsequently covered with finer soils Causes extensive problems when attempted for exploratory Causes extensive problems when attempted for exploratory

borings or to make excavations or drive pile foundations

Most alluvial soils have moderately good engineering Most alluvial soils have moderately good engineering properties

Typically provide fair to good support for buildings and Typically provide fair to good support for buildings and other structures

Lacustrine soilsLacustrine soils

Deposited beneath lakes May still be under water Or exposed due to lowering of lake water level

Primarily silt and clay Suitability for foundation ranges from poor to average Suitability for foundation ranges from poor to average

Marine soilsMarine soils

Deposited underwater in the ocean Deltas

Formed where rivers meet larger bodies of waterg Creates flat terrain – water flows very slowly Primarily silts and clays,--- very softPrimarily silts and clays, very soft

Beach sands – typically poorly graded, well rounded and looseloose

Deeper marine deposits M if More uniform

Often contain organic material from marine organisms

Most lacustrine and marine soils are very uniform and consistent

Engg. Properties are often poor but may be more gg p p ypredictable than the other more erratic soils

Aeolian soilsAeolian soils

Deposited by wind Produces very poorly graded soils

Due to strong sorting power of windg g p

Usually very loose Onl fair engineering properties Only fair engineering properties Three types of wind induced transport

Suspension Lifting individual silt particles to high altitude and transport

S l i Saltation Intermediate process—soil particles temporarily airborne and then fall

backback

Creep Occurs in particles too large to airborne – medium to coarse sands

Modes of sediment transport by the wind (after Pye, 1987)1987)

D t t i IDust storm in Iraq(after Lancaster 2009)

Forms sand dunesLoess- thick Aeolian silts

Colluvial soilsColluvial soils

Transported down by gravity Two types of movement

Slow In the order of mm per year, called CREEP

Rapidp Landslides or mudflows

Major Indian SoilsMajor Indian Soils

Black cotton soilsi i M h h G j M dh P d h K k f occurring in Maharashtra, Gujarat, Madhya Pradesh, Karnataka,parts of

Andhra Pradesh and Tamil Nadu. These are expansive in nature. On account of high swelling and shrinkage p g g g

potential these are difficult soils to deal with in foundation design

Marine soils occurring in a narrow belt all along the coast, especially in the Rann of Kutch.

These are very soft and sometimes contain organic matter, possess low strength and high compressibility.g g p y

Desert soils, occurring in Rajasthan. These are deposited by wind and are uniformly graded.

Alluvial soils occurring in the Indo-Gangetic plain, north of the Vindhyachal ranges.

Lateritic soils, occurring in Kerala, South Maharashtra, Karnataka, Orissa and West Bengal.

Visual identification of soils Water content determination