lecture slide

1. CE 206CE 206 Geotechnical EngineeringGeotechnical Engineering --IICE 206CE 206 Geotechnical EngineeringGeotechnical 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, g
theory, Shear strength of soils, Effective stress and total
stress strength parameters, Total and effective stressg p ,
paths, Compaction of soils.

2.  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 p
practices, 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)( )

3. Origin of SoilOrigin of Soil
CE 206CE 206 Geotechnical EngineeringGeotechnical Engineering IICE 206CE 206 Geotechnical EngineeringGeotechnical Engineering --II
Department of Civil Engineering
Indian Institute of Technology GuwahatiIndian Institute of Technology Guwahati

4. 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 crust
Soil is defined as the uncemented aggregate of mineral grainsSoil 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

5. 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

6. 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
water

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8. 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

9. Rock cyclesRock cycles
The final products
due to weathering aredue to weathering are
soils
(Das, 1998)

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

11. Rock MineralsRock Minerals
 Feldspar
 Quartz
 Ferromagnesian minerals Ferromagnesian minerals
 Iron oxides
C l i Calcite
 Dolomite
 Mica
 Gypsum Gypsum

12. 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

13. 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

14. 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

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

16. 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

17.  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

18. 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

19. 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

20.  Most lacustrine and marine soils are very uniform and
consistent
 Engg. Properties are often poor but may be moregg p p y
predictable than the other more erratic soils

21. 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

22. Modes of sediment transport by the wind (after Pye,
1987)1987)
D t t i IDust storm in Iraq
(after Lancaster 2009)
Forms sand dunes
Loess- thick Aeolian silts

23. 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

24. Major Indian SoilsMajor Indian Soils
 Black cotton soils
i 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 shrinkagep 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.

26.  Visual identification of soils
 Water content determination