KTU S4 Geotechnical Engineering PDF

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Summary

the application of scientific methods and engineering techniques to the exploitation and utilization of natural resources...

Description

GE I - syllabus •

Course Code

•

L-T-P-Credits

•

Course objectives:

•

1. To impart to the students, the fundamentals of Soil Mechanics principles.

•

2. To enable the students to acquire proper knowledge about the basic, index and engineering

CE208 4-0-0

Course Name

GEOTECHNICAL ENGINEERING - I

Year of Introduction 2019

properties of soils. •

syllabus :

•

Major soil deposits of India, Basic soil properties, Relationship between basic soil properties,

•

Index properties-Sieve analysis, Hydrometer analysis, Atterberg Limits and Relative density, Soil

•

classification, Permeability of soils, Principle of effective stress, Quick sand condition, Critical

•

hydraulic gradient, Shear strength of soils.

Contd. • Mohr-Coulomb

failure

criterion, Different

types

of

shear

tests,

Liquefaction of soils, Compressibility and Consolidation, Void ratio versus pressure relationship, Normally consolidated, under consolidated and over consolidated states, Estimation of magnitude of settlement,

Terzaghi€s

theory of one-dimensional consolidation, Coefficient of consolidation, Stability of finite slopes, Swedish Circle Method- Friction circle method, use of Stability, Compaction of soils, light and heavy compaction tests, Control of compaction

Contd. • •

Text Books: 1. Ranjan G. and A. S. R. Rao, Basic and Applied Soil Mechanics, New Age International, 2002.

•

2. Das B. M., Principles of Geotechnical Engineering, Cengage India Pvt. Ltd., 2010.

•

References:

•

1. Taylor D.W., Fundamentals of Soil Mechanics, Asia Publishing House, 1948.

•

2. Arora K. R., Geotechnical Engineering, Standard Publishers, 2006.

•

3. Venkatramaiah, Geotechnical Engg, Universities Press, 2000.

•

4. Terzaghi K. and R. B. Peck, Soil Mechanics in Engineering Practice, John Wiley, 1967.

• 5. Purushothamaraj P., Soil Mechanics and Foundation Engineering, Dorling Kindersley(India) Pvt. Ltd., 2013 • 6. A V Narasimha Rao and C Venkatramaiah, Numerical Problems, Examples and Objective questions in Geotechnical Engineering, Universities Press (India) Ltd., 2000

Course outcomes • To understand the importance of the subject Soil Mechanics and its implication in Civil engineering construction. • To make the students aware of the major soil deposits in India. • The understand the basic soil properties which influence the behavior of the soil, the field challenges and respective solutions. • To analyse the flow characteristics and the variation of stress with depth and complex phenomenon like quick sand condition and the aspects related to the design of earth dams and other retaining structures which are essential for a safe design

Course outcomes contd.

• To evaluate the shear strength of soil based on its strength parameters. • To understand the types of slope failures, analyse the slope stability and suggest remedial measures for slope failures . • To analyse the effect of placement water content in highway and airfield’s subgrade soil based on the type of soil.

Contd. COURSE PLAN

Module

Contents

Hours

Sem.Exa m Marks %

PART A – 30 marks – 10x3, 2 questions from each module PART B- One full qn. From each module- 5x14=70

I

Nature of soil and functional relationships : Introduction to soil mechanics – Soil types – Major soil deposits of India - 3 phase system – Basic soil properties : Void ratio, porosity, degree of saturation, air content, water content, specific gravity, unit weight Relationship between basic soil properties - Numerical problems Determination of Water content by oven drying, Specific gravity using pycnometer & specific gravity bottle - Determination of Field density by sand replacement method & Core Cutter method - Numerical problems Soil Structure and their effects on the basic soil properties – Sensitivity and Thixotropy

14%

II

Index properties : Sieve analysis – Well graded, poorly graded and gap graded soils - Stoke’s law – Hydrometer analysis [no derivation required for percentage finer and diameter] – Relative Density - Numerical problems - Consistency – Atterberg Limits and indices – Plasticity charts laboratory tests for Liquid Limit, Plastic Limit & Shrinkage Limit - Numerical problems IS classification of soil - Numerical problems Permeability of soils : Darcy’s law – Factors affecting permeability – Laboratory tests: Constant head and falling head permeability tests - Numerical problems - Average permeability of stratified deposits - numerical problems FIRST INTERNAL EXAM

14%

Contd.

III

Principle of effective stress - Total, neutral and effective stress – Pressure diagrams - Numerical problems - Pressure diagrams in soils saturated by capillary action – Quick sand condition – Critical hydraulic gradient Stress distribution : Introduction - Boussinesq’s equations for vertical pressure due to point loads and line loads – Assumptions and Limitations - Numerical problems - Vertical pressure due to uniformly distributed loads beneath strip, circular and rectangular shapes [no derivation required] Numerical problems Approximate methods for vertical stress-distribution of contact pressure beneath footings : Equivalent Point Load method & 2:1 Distribution Method - Numerical problems - Pressure Isobars - Pressure bulbs – Newmark’s charts (Construction procedure not required) and their use.

14%

IV

Consolidation - Definition – Concepts of Coefficient of compressibility and volume compressibility - e-log p curve - Compression index, Recompression index and Pre consolidation Pressure - Normally consolidated, over consolidated and under consolidated soils - Estimation of magnitude of settlement of normally consolidated clays - Numerical problems Terzaghi’s theory of one-dimensional consolidation (no derivation required) - average degree of consolidation – Time factor - Coefficient of consolidation - Numerical problems - Laboratory consolidation test – Determination of Coefficient of Consolidation Practical Applications Compaction of soils - Difference between consolidation and compaction - IS Light & HeavyCompaction Tests – OMC and MDD - Zero Air voids line - Numerical problems - Control of CIVIL ENGINEERING compaction - Field compaction methods - Proctor needle for field control

14%

Contd.

V

Shear strength of soils- Practical Applications - Mohr-Coulomb failure criterion - Mohr circle method for determination of principal planes and stresses– relationship between shear parameters and principal stresses - Numerical problems Brief discussion of Laboratory tests- Triaxial compression test - UU, CU and CD tests - Total and effective stress strength parameters - Unconfined compression test, Direct shear test and vane shear test – Applicability - Numerical problems Stability of finite slopes - Toe failure, base failure, slip failure - Swedish Circle Method : =0 analysis and c- analysis - Friction circle method - Taylor’s Stability number - Stability charts Numerical Problems END SEMESTER EXAMINATION

8 14%

Introduction to soil mechanics

Soil • Definition – Naturally occurring earth material (unconsolidated) • Organic or inorganic

– Lies above bed rock

• Word derived from – Latin word • Solium

– Meaning • Upper layer of earth’s crust

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Geotechnical Engineering SOIL ENGINEERING • Branch of Civil Engg • Deals with application of principles of – Mechanics – Hydraulics – Chemistry

• To engg problems related to soils

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ROCK ENGINEERING

• Branch of Civil Engg • Deals with application of principles of – Mechanics – Chemistry

• To engg problems related to rocks

Introduction contd… • Soil has various meanings • Agriculturist – substance existing on the earth’s surface which grows and develops plant life • Geologist – thin surface zone within which roots occur, rest of the crust is rock irrespective of its hardness • Engineer – it is unaggregated or uncemented deposits of minerals or organic particles or fragments covering large portion of the earth’s crust. • Includes materials like boulders, gravels, clays and silts • Vast field with various engg. applications

Contd. • Soil mechanics or Geotechnical Engineering is one of the disciplines of Civil Engineering • According to Terzaghi (1948) soil mechanics is the application of 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 they contain an admixture of organic constituent

Karl Von Terzaghi • • •

•

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Father of Soil Mechanics 02 Oct 1883 - 25 Oct 1963 Works – Erdbaumechanik auf Bodenphysikalischer Grundlage (The Mechanics of Earth Construction Based on Soil Physics) (1924) – Theoretical Soil Mechanics (1943) – Soil Mechanics in Engineering Practice · From Theory to Practice in Soil Mechanics (1960) Fields of interest – Consolidation – Bearing capacity – Earth Pressure – Settlement – Permeability

Field of soil mechanics • Foundation design and construction • Pavement design • Design of underground and earth retaining structures • Design of embankment and excavation • Design of earth dams

Contd. • Soil engineering – practical science rather than mathematical one • Foundation engineering is a branch of civil engineering associated with design, construction, maintenance, and renovation of footings, foundation walls, pile foundations, caissons and all other structural members which form the foundations of buildings and other engineering structures (Taylor 1948)

ORIGIN OF SOILS

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Contd. • Soil is a complex material produced by weathering of solid rock. • It is formed as a result of geological cycle taking place on the surface of earth • Cycle consists of weathering, transportation, deposition and upheaval again followed by weathering and so on. • Weathering caused by flowing water, ice and wind, splitting action of ice, plants , animals etc.

Contd. • Cohesionless soil – physical disintegration of rocks • Chemical weathering caused by oxidation hydration, carbonation and leaching by organic acids and water • Clay minerals by chemical weathering • Residual or transport • Residual soils at shallow depth

Contd. • Transported soil at considerable depth • Homogeneity or heterogeneity depends on manner of their transportation • Agencies of transportation • Water, ice, wind, gravity • Water – alluvial, marine or lacustrine (deposits are sedimentary rock formations which formed in the bottom of ancient lakes. A common characteristic of lacustrine deposits is that a river or stream channel has carried sediment into the basin) • Wind – aeoline (wind deposited sand) dune sand (ridge), loess • Loess- wind blown silt or silty clay

Contd. • Gravitational force – colluvial soils (loose unconsolidated sediments), talus( mixture of boulders, gravel, silt and clay) • Decaying and chemically deposited vegetables • Cumulose soil, peat and muck

Medium of Type of soil transportation

Soil types and deposits

Deposit

Water

Alluvial soil Lacustrine (Sedimentary deposits soil) Marine deposits

Wind

Aeolian soil

Loess

Gravitational force

Colluvial soil

Talus

Glacier

Drift (Glacial soil)

Till

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Alluvial Soil, Alaska

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Colluvial Soil

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Aeolian soil, China

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Glacial Soil, Australia

Soil groups • Some of the major soil groups available in India are 1. Alluvial Soils 2. Arid and Desert Soils 3. Black cotton Soils 4. Laterite and Lateritic Soils 5.Red Soils 6. Forest and Mountain Soils 7. Saline and Alkaline Soils 8. Peaty and Marshy Soils.

Contd. • Alluvial soils (fine grained fertile soil deposited by water flowing over flood plains) • Alluvial soil is most wide spread. • These are found in the entire northern plains • Desert soils • found in Thar desert in the state of Rajasthan • Black soils • Central India and Deccan plateau mainly constitutes this type of soil

Black soil • Black soils are derivatives of trap lava and are wide spread. These are mostly clay soils and form deep cracks during dry season. An accumulation of lime is generally noticed of varying depths. They are popularly known as “Black cotton soils” • These soils are made up of volcanic rocks and lavaflow. It is concentrated over Deccan Lava Tract which includes parts of Maharashtra, Chhattisgarh, Madhya Pradesh, Gujarat, Andhra Pradesh and Tamil Nadu. Typical characteristics of this black soil are swelling (during wet period) and shrinkage (dry period).

Contd. • They cover the plateaus of Maharashtra, Saurashtra, Malwa, Madhya Pradesh, Chhattisgarh and extend in South-East direction along Godavari and Krishna valleys. • These soils contain essentially clay minerals as montmorillonite • Lateritic Soils • Lateritic soils are formed from chemical decomposition of rocks

Cotd. • These soils mainly contain iron oxide which gives them characteristic pink or red color. These are residual soils formed from basalt and have high specific gravity. These soils are mostly composed as calcite depositions. • Laterite –it is a rock type rich in iron and aluminum, formed in hot and wet tropical areas • Laterite and lateritic soils are widely spread in India and cover an area of 2.48 lakhs sq. km

Contd. • Found in Central, Eastern and South India , summits of Western Ghats at 1000 to 1500 m above mean sea level, Eastern Ghats, the Rajamahal Hills, Vindhyas, Satpuras and Malwa Plateau. Well developed in south Maharashtra, parts of Karnataka, Andhra Pradesh, Orissa, West Bengal, Kerala, Jharkhand, Assam and Meghalaya.

Contd. • Red soils are formed by weathering of the ancient crystalline and metamorphic rocks. Their color is red due to their very high iron content. They are found in areas of low rainfall and is obviously less leached than laterite soils. Red Soil in India are poor in phosphorus, nitrogen and lime contents.

Contd. • Red Soil in India is largely available in the Deccan Plateau. It is mainly seen in Periyar and Salem in the state of Tamil Nadu. In India, red soil is also found in several other regions including Madhya Pradesh, Andhra Pradesh,Southern Karnataka, Bihar, Maharas htra, Goa, Eastern Rajasthan, West Bengal and other states of North-East .

Contd. • The north-western portions of the peninsular block is covered by black soil while the rest south-eastern half is covered by red soil of various shades of yellow and red. Red soils have matured on older crystalline rocks, under deep and rational rainfall conditions

Contd. • They basically surround the whole black soil region on all sides, and cover the eastern part of the peninsula, comprising Chota Nagpur Plateau, Orissa, eastern regions of Madhya Pradesh, Telangana, Tamil Nadu plateau and Nilgiri Hills.

Contd. • Marine deposits • These soils are found in narrow belt near the south-west coast of India. These soils have low shearing strength and high compressibility. They contain large amount of organic matter and are not suitable for construction of mega structures like buildings, cranes etc

Forest & mountain soil • Such soils are mainly found on the hill slopes covered by forests. These soils occupy about 2.85 lakh sq km which is about 8.67 per cent of the total land area of India. The formation of these soils is mainly governed by the characteristic deposition of organic matter derived from forest growth. Heterogeneous in nature.

Contd. • In the Himalayan region, such soils are mainly found in valley basins, depressions, and less steeply inclined slopes. forest soils occur on Western and Eastern Ghats as well as in some parts of the Peninsular plateau.

Contd. • Arid & desert soil • A large part of the arid and semi-arid region in Rajasthan and adjoining areas of Punjab and Haryana lying between the Indus and the Aravalis, covering an area of 1.42 lakh sq km (or 4.32% of total area) and receiving less than 50 mm of annual rainfall, is affected by desert conditions. • Coastal regions of Orissa, Tamil Nadu and Kerala

Contd. • Saline and alkaline soil • These soils are found in Andhra Pradesh and Karnataka. In the drier parts of Bihar, Uttar Pradesh, Haryana, Punjab, Rajasthan and Maharashtra, there are salt-impregnated or alkaline soils occupying 68,000 sq km of area. These soils are liable to saline and alkaline efflorescence and are known by different names such as reh, kallar, usar, thur, rakar, karl and chopan.

Contd. • Peaty and marshy soil • Peaty soils originate in humid regions as a result of accumulation of large amounts of organic matter in the soils. These soils contain considerable amount of soluble salts and 1040 per cent of organic matter. Soils belonging to this group are found in Kottayam and Alappuzha districts of Kerala where it is called kari.

Contd. • Marshy soils with a high proportion of vegetable matter also occur in the coastal areas of Orissa and Tamil Nadu, West Bengal, in Bihar and Almora district of Uttaranchal. The peaty soils are black, heavy and highly acidic. They are deficient in potash and phosphate. Most of the peaty soils are under water during the rainy season but as soon the rain cease, they are put under paddy cultivation.

Basic soil properties • Soil mass – three phase system • Soil grains, water and air • Void space b/w soil grains partly filled with water and partly with air • Dry soil – filled with air • Saturated soil – water • Soil mass has three constituents- do not occupy separate spaces but are blended together forming a complex material

Contd.

Contd.

Contd. • Total volume V of soil mass consists of i) volume of air, Va ii) volume of water, Vw and iii) volume of solids, Vs. • Volume of voids Vv = Va + Vw • Weights • Weight of air = 0 • Weight of total voids = Wt. of water = Ww • Wt. solids = Wd or Ws= dry wt. of soil • Total wt. W = Ww + Wd

BASIC FORMULAE • Void ratio,

e = Vv / Vs

• Porosity,

n = Vv / V

• Degree of saturation,

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S = Vw / Vv

• Air content,

ac = Va / Vv

• Air Porosity, (% air voids)

na = Va / V

BASIC FORMULAE • Water content,

w

=

Ww / Ws

• Bulk unit weight, Bulk density,

=

W/V

• Dry unit weight, dry density,

=

Ws / V

=

Wsat / V

= = = =

Wsub / V sat - w Ws / Vs s/ w

d

• Saturated unit weight,

sat

• Submerged unit weight,

I

• Unit weight of soil solids, s • Specific gravity, G Mass sp. Gravity Gm= /

w , w = Ww/Vw<...