01 - NPTEL · strain behaviour: Isotropic compression and pressure dependency, confined compression, large stress compression, Definition of failure, Interlocking concept and its

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay

01


Advanced Geotechnical Engineering

Dr.-Ing. B.V.S. Viswanadham

Professor, Department of Civil Engineering

Indian Institute of Technology Bombay

Powai, Mumbai- 400 076, INDIA

Website: www.civil.iitb.ac.in/~viswam

Email: [email protected]


Course OutlineOrigin and the nature of soils as engineering materials; Soil classification schemes; Clay mineralogySoil compaction; Soil-water interaction; Permeability and Seepage Consolidation behaviour of the soil and Methods for accelerating consolidation of the soil.The stress-strain-strength response of soils, Earth retaining structures and stability analysis of slopesBuried structures, and Geotechnical physical modelling


S.No. Module Contents

1. Soil composition and soil structure

Soil formation; Types of soils and theircharacteristics; Particle sizes and shapes;their impact on engineering properties;Soil structure; Clay mineralogy; Soil-air-water interaction; Consistency; Soilcompaction; Concept of effective stress.



2. Permeability and Seepage

Permeability; Seepage force andeffective stress during seepage; Laplaceequations of fluid flow for 1-D, 2-D and3D seepage, Flow nets, Anisotropic andnon-homogeneous medium, Confinedand Unconfined seepage.



3. Compressibility and Consolidation

Stresses in soil from surface loads;Terzagahi’s 1-D consolidationtheory; Application in differentboundary conditions; Ramploading; Determination ofCoefficient of consolidation cv;Normally and Overconsolidatedsoils; Compression curves;Secondary consolidation; Radialconsolidation; Settlement ofcompressible soil layers andMethods for acceleratingconsolidation settlements.



4. Stress-strain relationship and Shear strength of soils

Stress state, Mohr’s circle analysis andPole, Principal stress space, Stresspaths in p-q space; Mohr-coulombfailure criteria and its limitations,correlation with p-q space; Stress-strain behaviour: Isotropiccompression and pressuredependency, confined compression,large stress compression, Definition offailure, Interlocking concept and itsinterpretations, Drainage conditions;Triaxial behaviour, stress state andanalysis of UC, UU, CU, CD, and otherspecial tests, Stress paths in triaxial andoctahedral plane; Elastic modulus fromtriaxial tests.



5. Earth retaining structures

Earth pressures; Stress changes in soilnear retaining walls; Earth pressuretheories- estimation of earthpressures-drained and undrainedloading.

6. Stability of Slopes

Stability analysis of a slope andfinding critical slip surface; SuddenDraw down condition, effective stressand total stress analysis; Seismicdisplacements in marginally stableslopes; Reliability based design ofslopes, Methods for enhancingstability of unstable slopes.



7. Buried Structures Load on Pipes, Marston’s loadtheory for rigid and flexible pipes,Trench and Projection conditions,minimum cover, Pipe floatationand Liquefaction.

8. Geotechnical Physical Modeling

Physical modeling methods;Application of centrifuge modelingand its relevance to geotechnicalengineering; Centrifuge modelingof geotechnical structures.


Geotechnical engineering is the branch of CivilEngineering concerned with the engineeringbehaviour of earth materials. Geotechnicalengineering uses principles of *Soil Mechanics and**Rock Mechanics to investigate subsurfaceconditions and materials

*Soil Mechanics is the branch of science that deals with thestudy of the physical properties of soil and the behaviour ofsoil mass subjected to various types of forces.

**Rock mechanics is the theoretical and applied science of the mechanical behaviour of rock and rock masses


Examples of geotechnical engineering construction

Natural slope

Cut slope

Embankment dam

Building foundation



Supported excavation

Tunnel

Buried pipe

Road embankment

Geosynthetic Reinforced wall

Building on pile foundation



AshAsh Compacted

ash

Compacted ash

Conventional/Bioreactor landfills

Heterogeneous Municipal Solid

Waste



Offshore foundation

Construction on soft soil

Sea wall

Windmill foundation


Typical geotechnical failures…

Landfill failure

Expansive soil subgrade Mud pumping

Landslide

Slope failure Track

subsidence


Geotechnical Engineering is simply the branch ofengineering that deals with structures built of, or in,natural soils and rocks.

This subject requires knowledge of strength andstiffness of soils and rocks, methods of analyses ofstructures and hydraulics of ground water flow.


Course Context

An understanding of the engineeringbehaviour of the ground and the interactionbetween the ground and any structures built inor on the ground is essential for all CivilEngineers.


According to Karl Terzaghi (1883-1963):

“Unfortunately, soils are made by nature and not by man, and the products of nature are always complex…

As soon as we pass from steel and concrete to earth, the omnipotence of theory ceases to exist. Natural soil is

never uniform. Its properties change from point to point while our knowledge of its properties are limited to those few spots at which the samples have been collected. In soil mechanics the accuracy of computed results never

exceeds that of a crude estimate, and the principal function of theory consists in teaching us what and how

to observe in the field.”


Selected ReferencesAtkinson, J. (2007). The mechanics of soils andfoundations. Taylor & Francis, London and New York,Second Edition.

Aysen, A. (2005). Soil Mechanics: Basic Concepts andEngineering Applications, Taylor & Francis, London andNew York, First Edition.

Craig, R.F. (2004). Craig’s Soil Mechanics, Spon PressTaylor & Francis, London and New York, SeventhEdition.

Das, B.M. (2008). Advanced Soil Mechanics. Taylor &Francis, London and New York, Third Edition.


Selected ReferencesFang, H-Y., and Daniels, J.L. (2006). IntroductoryGeotechnical Engineering: an EnvironmentalPerspective. Taylor & Francis, London and New York,First Edition.

Fredlund, D.G., and Rahardjo, H. (1993). Soil mechanicsfor unsaturated soils, John Wiley & Sons, New York, FirstEdition.

Holtz, R.D., and Kovacs, W.D. (1981). An introduction togeotechnical engineering, Prentice Hall, New Jersey,

Kaniraj, S.R. (2008). The mechanics of soils andfoundations, Tata McGraw-Hill Publishing CompanyLtd., New Delhi, Tenth Reprint.


Selected ReferencesMcCarthy, D.F. (2007). Essentials of Soil Mechanics andFoundations: Basic Geotechnics, Pearson Prentice Hall,New Jersey, Ohio, Seventh Edition.

Parry, R.H.G. (2004). Mohr circles, stress paths andGeotechnics. Spon Press Taylor & Francis, London andNew York, Second Edition.

Wood, D.M. (2004). Geotechnical Modelling, Spon PressTaylor & Francis, London and New York, First Edition.


• The rocks that form the earth’s surface are classified as to origin as:

• - Igneous • - Sedimentary• - Metamorphic

Rock: The source of soilsMost of the nonroganic materials that are identified as soil originated from rock as the parent material.


Igneous Rocks• are those formed directly from the molten state of magma. The molten magma that cooled rapidly at or near earths surface are called

extrusive or volcanic type rocks. Eg. Basalts, Rhyolites and Andesites. If the molten rock cools very slowly, the different materials segregate into

large crystals forming a coarse-grained or granular structure (Trapped atdeeper depths)Intrusive or plutonic type, Eg. Granite (which consists of quartz and

feldspar), Syerites, and Gabbros Because of high silica content these rocks are classified as ACIDIC

Decomposes to predominantly sandy or gravel with little clay. (Good constructionmaterials!)

Rocks whose minerals contain Fe, Mg, Ca or Na but little silica such as theGabbros, Diabases, Basalts are classified as BASIC


Igneous RocksWhen the solution of magma is cooled very very rapidly theminerals do not separate into crystals but solidify as amorphousvitreous rock.

Such as, Volcanic Scoria, Pumice, and Obsidan Rock types that are intermediate between acidic and basicinclude the Trachytes, Diorites, and Andesites

Easily break down into the fine-texturedsoils due to their mineral components.

The clay portion of fine-textures soil is the result of primaryrock minerals decomposing to form secondary minerals.

Not small fragments of the parent rock minerals The properties and behaviour of clay soils are different fromthose of gravel, sand, and silt soils.


Sedimentary Rocksare formed from accumulated deposits of soil particles

or remains of certain organisms that have becomehardened by pressure or cemented by minerals.Cementing materials such as silica, CalciumCarbonate, iron oxides are abundant

For E.g., Limestones, *Dolomites, Sandstone, Shale, Conglomerate and Breccia

*Dolomite is referred to both the rock forming mineral CaMg(CO3)2 and sedimentary rock (recent name is Dolostone)


Sedimentary rocksShales are predominantly formed from deposited clay and silt particles.

- The degree of hardness = f ( the type of minerals, the bondingthat developed, and the presence of foreign materials).

- The hardness is mainly due to external pressures and particlebonds, not due to cementing minerals.

- When exposed to environment (water or air), shales tend toexpand or delaminate (the layers separate)

- Break down of shale fragments of varying sizes Clayparticle sizes


Formation of sinkholes

(Modified after: http://geoservicesltd.com/Limestonesinkholes.html)

Sedimentary rocks Limestone is predominantly crystalline CaCO3(Calcite) formed under water. Limestone-Dolomite is referenced as Karst orKarstic terrain.

Sinkholes/cavities canresult due to solvablenature with ingredientspresent in ground water.Weathering of limestones predominantly finer size

particles.


• Metamorphic Rocks [Source: IR or SR]- results when any type of existing rock issubject to metamorphism, the changebrought about by combinations of heat,pressure and plastic flow so that the originalrock structure and mineral composition arechanged.[ Plastic flow – slow viscous movement andrearrangement within the rock mass due to externalforces]Limestone MARBLE; Shale SLATE or PHYLLITE; Granite GNEISS; Sandstone QUARTZITE


Metamorphic Rocks

Gneiss is a foliated rock with distinctive bandingthat results from the metamorphosis of granite.

Distinction between Gneisses and Schists is notalways clear

Upon weathering Gneiss and Schist decompose toform silt-sand mixtures with mica.

Soils from phyllites are more clayey anddecomposition of quartzite produces sands andgravels.


Typical example of metamorphism


ROCKS(IGNEOUS, SEDIMENTARY, METAMORPHIC)

WEATHERING(PHYSICAL/CHEMICAL)

TRANSPORTED

BOULDERS, GRAVEL, SAND, SILT AND CLAY

SOIL


• Rocks whose chief mineral is quartz minerals with high silica content, decomposes to predominantly sandy or gravelly soil with little clay. [Acidic rocks are light-coloured]

• Basic rocks decompose to the fine-textured silt and clay soils.

- The clays are not small fragments of the original materials that existed in the parent rock [ result of primary rock minerals decomposing to form secondary minerals]


Major soil types based on particle sizeThe major engineering categories of soil are gravel, sand, silt and clay

Gravel and sands are considered coarse-grained soils (with large bulk particle sizes) Silt (very tiny particles of disintegrated rock) and clay particlesare considered fine-grained soils because of their small particlesizes.

- Clay soil is plastic (if it can be remolded withoutcracking/breaking) over a range of water content and silt soilpossesses little or no plasticity.

Particles larger than gravel are called cobbles or boulders


• Soils can be grouped into two broad categories (depending on the method of deposition):

Residual – Formed from weathering of rock and remain at the location of their origin.

[a material which may possess little mineralogical resemblance to the parent rock] Transported – those materials that have been moved from their place of origin- by agencies like, gravity, water, glaciers, or man- either singularly or in combination


• Characteristics of Residual soils are dependent on: Climatic conditions - humidity, temp., rainfall)

Natural drainage pattern

Form and extent of vegetation cover[A warm and humid climate is favourable to theformation of residual soils and nature of residual soildiffers markedly at different depths below groundsurface and constantly changes with time]- Soil deposits in Deccan Plateau


• Transported Soils are classified according to the transporting agency and method of deposition:

Alluvial – transported in running water [rivers] Lacustrine – deposited in quiet lakes Marine – deposited in sea water Aeolin – transported by wind Glacial – by ice [Glaciation –

massive moving sheets of ice Colluvial – deposited through action of landslide

and slope wash


Examples of Transported soils:

LOESS – Wind blown deposit with very uniform fine silt particles (possesses slight cementation properties)

– Formed in Arid and Semi-Arid regionswith yellowish light brown colour

Tuff – Fine-grained slightly cemented volcanic ash [by wind/water]

Glacial till – Heterogeneous mixture of boulders, gravel, sand, silt and clay [Hilly regions]


Examples of Transported soils: Varved Clay – Alternate layers of silt and clay

deposited in fresh water glacial lakes.- One band of silt and clay deposited each year [each layer is approx. 10 mm thk.]

Marl – Very fine grained soil of marine origin [impermeable, greenish colour]

Peat – A highly organic soil consisting almost entirely of vegetable matter in varying stages of decomposition, Fibrous, brown to black in colour and highly compressible


Major soil deposits: f( Ambience, Geography and Topography)

Expansive – High shrink-swell characteristics(attributed to the mineral)Colour- Black (presence of Fe, Mg and Ti)

Marine – Very soft and may contain organic matter Laterite – Red in colour due to Fe2O3 (Laterization-

Leaching of Silica – due to intense chemical weathering)

Alluvial – Alternate layers of Sand, Silt and Clay Desert – Wind blown, Uniformly graded Glacial – Boulder clay (all ranges of particle sizes)


Distribution of predominant Soil deposits In India

Marine soil deposits

Expansive soil deposits

Desert soils


Constituents of the soil mass

-Formation of soils from the weathering of the parent rock

-Wide range of sizes of soil solidsBehaviour of soil mass under stress is a function of material properties, such as:(i) size and shape of grains, (ii) gradation, (iii) mineralogical composition, (iv) arrangement of grain, (v) inter-particle forces, etc.)

Material properties f(constituents of the soil mass)


Soil is a particulate material,

which means that a soil mass consists of accumulation ofindividual particles that are bonded together bymechanical or attractive means, though not strongly as forrock.

- Spaces in between solid particles Voids or pore space


In soil (in most rock), voids exist between particles, and voids may be filled with a liquid, usually water or gas, usually air.


Water surrounding particles and at points of contact between particles, and filling small void spaces

Air in irregular spaces between soil particles

Actual soil bulk consisting of soil particles, water and air



Soil is inherently multiphase material(Generally consists of three phases)

- Solid phase- Liquid phase- Gaseous phase

It can also be TWO PHASE material:

- With solid + Gaseous (DRY STATE)

- With solid + Liquid (SATURATED STATE)


3 – Phase system

SOLIDS

LIQUID

GAS

Idealization


Solid phase consists of:

Primary rock forming minerals (Size > 2µm, Poor Reactivity, Prone to disintegration)

Clay minerals (Basic materials that form the soil mass, Size < 2µm, High Reactivity)

Cementing material (Carbonates)

Organic matter (High water absorption, Compressible, unstable)


Liquid phase consists of:

WATER DISSOLVED SALTS

Pure water

Polluted water

Water soluble

Water insoluble

Water soluble- Chlorides, Sulphates, Bicarbonates (Not capable of binding solid grains)


Gaseous phase consists of:

2 –phase system; Dry soil

AIR GASES

Solids

Air

Solids

Water

2 –phase system; Saturated soil


3 – Phase system

Wa = 0

Weight

=

SOLIDS

WATER

AIR

Volume

Va

Vw

Vs

VVWw

Ws

V = VS+VW+Va W = WS + WW

Partially Saturated Soil


3 – Phase system

Wa = 0

Weight

=

SOLIDS

WATER

AIR

Volume

Va

Vw

Vs

VVWw

Ws

V = VS+VW+Va W = WS + WW

Partially Saturated Soil


Self evaluationi) List the soil types included in coarse-grain

category and the fine-grain category

ii) Why there is a difference in behaviour of naturalclays and other soil types such as sands and silts?

iii) What does the term plastic mean in relation toclay soils?

iv) What are laterites (or lateritic soils) and why aresuch soils considered in the category of requiringspecial consideration on construction projects?

v) From any borehole data in your location, list soiltype and rock types

Documents

01 - NPTEL · strain behaviour: Isotropic compression and pressure dependency, confined compression, large stress compression, Definition of failure, Interlocking concept and its