University of Salahaddin – Erbil College of Engineering Water Resources Department

Course book

Soil Mechanics

Omed A. Azeez

B.Sc. in Civil Engineering M.Sc. in Soil Mechanics and Geotechnical Engineering

Email: omed.azeez@su.edu.krd

Third year

Four hours per week

2020-2021

Important Note: Attendance: Students are required to attend lectures. The maximum absence is 12 hours for both courses.

Courses Objective 1- To learn students what are principles of soil Mechanics (Weathering, clay minerals, stress within soils, etc…) and how to find them. 2- How to a p p l y these principles in the real life (engineering projects). Introduction

Soil mechanics is a branch of engineering mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and water) a n d particles (usually clay, silt, sand, and gravel) but soil may also contain organic solids, liquids, gasses and other matter.

A-Theoretical part Chapter 1: Basic characteristics of soils 1.1 Definitions 1.2 Uniqueness of soils 1.3 Examples of Soil Mechanics problems 1.4 Origin of Soil 1.5 Swelling and shrinkage of clays 1.6 Activity of soils Chapter 2: Soil description and classification 2.1 Particle size analysis 2.2 Procedure for grain size determination 2.3 Classification of soil 2.4 Problems Chapter 3: Soil phase relationships Problems Chapter 4: Compaction of soils 4.1 Relative density 4.2 Laboratory compaction test 4.3 Specification of compaction in the field 4.4 Field compaction methods 4.5 Field density determinations 4.6 California bearing ratio test Chapter 5: Permeability and seepage 5.1 Soil in water and heads 5.2 Permeability 5.3 Seepage theory 5.4 Flow nets 5.5 Anisotropic soil conditions 5.6 Non-homogeneous soil conditions

5.7 Seepage through embankments 5.8 Problems Chapter 6: Stress within a soil mass 6.1 Introduction 6.2 The principle of effective stress 6.3 Response of effective stress to a change in total stress 6.4 Influence of seepage on effective stress 6.5 Stress in soil due external surface loads 6.6 Problems Chapter 7: Shear strength of soil 7.1 Shear failure 7.2 Shear strength tests 7.3 Shear strength of sands 7.4 Shear strength of saturated clays 7.7 Pore pressure coefficients 7.8 Problems Chapter 8: Compressibility and consolidation of soil 8.1 Introduction 8.2 The odometer test 8.3 Consolidation settlement:one-dimensional method 8.4 Settlement by the Skempton-Bjerrum method 8.5 The stress path method 8.6 Degree of consolidation 8.7 Terzaghi's theory of one-dimensional consolidation 8.8 Determination of coefficient of consolidation 8.9 Correction for construction period 8.10 Problems Chapter 9: Slope stability 9.1 Introduction 9.2 Analysis for the case of Ф=0 9.3 The method of slices 9.4 Analysis of a plane translational slip 9.5 General methods of analysis 9.6 End-of-construction and long-term stability 9.7 Embankment dams 9.8 Problems Chapter 10: Lateral earth pressure 10.1 Introduction 10.2 Rankine's theory of earth pressure 10.3 Coulomb's theory of earth pressure 10.4 Application of earth pressure theory to retaining walls 10.5 Problems

Chapter 11: Soil Investigations 11.1 Philosophy of site investigation 11.2 Objectives of Site Investigation 11.3 The Desk Study 11.4 Borehole layout & frequency 11.5 In situ testing (strength & stiffness) B- Practical part-Laboratory tests Test 1: Water content Test 2: Specific gravity. Test 3: Sieve analysis Test 4: Hydrometer Test 5: Liquid and plastic limits Test 7: Permeability test Test 8: Direct shear Test 9: Unconfined compression test Test 10: Triaxial test Test 11: Consolidation test

Chapter 1: Basic characteristics of soils and soil classification. Soil Composition

The primary mechanism of soil creation is the weathering of rock. All rock types (igneous rock, metamorphic rock and sedimentary rock) may be broken down into small particles to create soil.

Weathering mechanisms are physical weathering, chemical weathering, and human activities such as excavation, blasting, and waste disposal, may also create soil.

Clay minerals: such as Quartz, illite, kaolinite etc…

Examples of Soil Mechanics problems: Leaning Tower of Pisa

Chapter 2: Soil classification. According to the Unified Soil Classification System (USCS), silt particle sizes are in the range of 0.002 mm to 0.075 mm and sand particles have sizes in the range of 0.075 mm to 4.75 mm. Silt, Sand, and Gravel are basically little pieces of broken rocks. Gravel particles are broken pieces of rock in the size range 4.75 mm to 100 mm. According to the Unified Soil Classification System, particles larger than gravel are called cobbles and boulders. Soil Classification Geotechnical engineers classify the soil particle types by performing tests on disturbed (dried, passed through sieves, and remolded) samples of the soil. This provides information about the characteristics of the soil grains themselves.

Classification of sands and gravels In the USCS, gravels (given the symbol G) and sands (given the symbol S) are classified according to their grain size distribution.

Classification of silts and clays According to the USCS, silts and clays are classified by plotting the values of their plasticity index and liquid limit on a plasticity chart. Example (USCS) Sieve analysis on four different samples designated as A, B, C and D were carried out in a soil laboratory. The results of tests are given below. Hydrometer analysis was carried out on sample D. The soils A, B, and C are non-plastic. Classify the soils per the Unified Soil Classification System.

Samples ASTM Sieve

% finer Soil A Soil B Soil C Soil D

63 mm 100 - 93 - 20.0mm 64 - 76 - 6.3mm 39 100 65 - 2.0mm 24 98 59 -

600µmm 12 90 54 - 212µmm 5 9 47 100 63µmm 1 2 34 95

20µmmmm - - 23 69 6µmm - - 7 46 2µmm - - 4 31 L.L % - - - 42 P.L% 24

Chapter 3: Soil phase relationships. Mass-volume relations

There are a variety of parameters used to describe the relative proportions of air, water and solid in a soil.

Soil phases (solids, liquids, and gases) Examples of some relations

Chapter 4: Compaction of soils Relative density (Dr%)

where emax, emin, and e are the maximum, minimum, and in-situ soil’s void ratios, respectively. When the in-situ soil’s void ratio is in its loosest (e = emax) state, then, Dr = 0%.

Laboratory compaction test

Example compaction curve.

Field compaction methods

Compaction Equipment Pneumatic rubber tire rollers Sheep’s-foot rollers Smooth-wheel (drum) rollers Vibratory wheels There are several key parameters that influence field compaction in addition to the level of compaction energy and controlling the water content as close as possible to its optimum water content. Number of passes:

Sheep’s-foot rollers

Sand cone method Chapter 5: Permeability and seepage.

Seepage: steady state flow of water If fluid pressures in a soil deposit are uniformly increasing with depth according to u = ρw. z then hydrostatic conditions will prevail and the fluids will be not be flowing through the soil.

Typical values of permeability Values of the permeability, k, can vary by many orders of magnitude depending on the soil type. Clays may have permeability as small as about ,

gravels may have permeability up to about . Layering and heterogeneity and disturbance during the sampling and testing process make the accurate measurement of soil a very difficult problem.

Flow Net The quantity of seepage (volume /time) in seepage problems and uplift water pressure on base of Structure used to retain or store water can be studied by flow net .The flow of water through a soil can be represented graphically by means of a flow net , which consists of flow lines and equipotential lines. Criteria for sketching flownets A flownet must meet the following criteria: 1. The boundary conditions must be satisfied. 2. Flow lines must intersect equipotential lines at right angles. 3. The area between flow lines and equipotential lines must be curvilinear squares. A curvilinear square has the property that an inscribed circle can be drawn to touch each side of the square and continuous bisection results, in the limit, in a point. 4. The quantity of flow through each flow channel is constant. 5. The head loss between each consecutive equipotential line is constant. 6. A flow line cannot intersect another flow line. 7. An equipotential line cannot intersect another equipotential line. 8. An infinite number of flow lines and equipotential lines can be drawn to satisfy Laplace’s equation. However, only a few are required to obtain an accurate solution. The procedure for constructing a flownet is described next.

Flownet for a sheet pile

Chapter 6: Stress within a soil mass.

Soils are stable under the existing effective overburden stresses. However, when additional loads are placed on the ground surface, such as by footings, traffic loads, etc., those additional loads increase the stresses in the soil mass. These extra stresses are major sources of the settlement of soils. In this chapter, equations for the vertical stress increments in soil mass due to various types of load on the ground surface are discussed. Effective stress, hydrostatic conditions and capillarity.

Chapter 7: Shear strength of soil

Shear strength of a soil (τf) is the maximum internal shear resistance to applied shearing forces.

Learning outcomes When you complete this chapter, you should be able to do the following:

• Understand the concept of shear strength of soils. • Understand typical stress–strain behavior of soils. • Understand the differences between drained and undrained shear strength. • Interpret laboratory and field test results to obtain shear strength parameters. • Determine the type of shear test that best simulates field conditions.

Some practical cases and laboratory tests to specify.

Response of soils to shearing.

Chapter 8: Compressibility and consolidation of soil

Elastic settlement is the settlement of a geosystem that can be recoverable upon unloading. Consolidation is the time-dependent settlement of soils resulting from the expulsion of water from the soil pores. Primary consolidation is the change in volume of a fine-grained soil caused by the expulsion of water from the voids and the transfer of stress from the excess porewater pressure to the soil particles.

Figure (a) A typical consolidation apparatus, (b) a fixed ring cell, and (c) a floating ring

cell.

e-log σ curve.

Chapter 9: Slope stability

Natural or artificially constructed slopes may be stable at present but they might lose their stability and cause collapse of slopes. When this happens, the collapse can be sudden and catastrophic and many properties and lives can be lost. This chapter first examines the mechanism of slope failure and analytical procedures for the slope stability are presented. Then, when the stability of slope is questioned, several possible preventive measures are discussed.

Example of possible slip surface

Chapter 10: Lateral earth pressure When engineers face the designing of earth-retaining structures, bridge abutments, basement structures, sheet piles, support for excavated trenches, etc., a proper estimation of lateral earth pressure against these structures becomes most critical.

1. At rest earth pressure 2. Active earth pressure 3. passive earth pressure

Chapter 11 :Soil Investigations How drilling in ground ,getting undisturbed and disturbed samples ,S.P.T tests.

Grading

Classroom activities, quizzes, homework, and final exam on June. So that the final grade will be based upon the following criteria:

Theoretical Part

- Midterm exam 15 %

- Second semester exam 15 %

- Activities 10 %

- Final Exam 40%

Practical Part

- Reports 6%

- First semester exam 2%

- Second semester exam 2%

- Final Exam 10 %

- Total Grade 100% References:

1. Principals of Geotechnical Engineering, 2019. Braja M. Das, 9th edition. 2. Craig s Soil Mechanics, 2014. R.F. Craig, 8 Edition 3. Core Principles of Soil Mechanics, ICE textbooks, 2014. Sanjay K. Shukla. 4. Soil Mechanics: Concepts and Applications, 2014. William Powrie, 3rd edition. 5. Soil Mechanics, 1995. G. E. Barens. 6. Soil Mechanics, 1979. T. W. Lambe and Robert V. Whitman. 7. Soil Mechanics and Foundation Engineering, 2002. DR. K. R. Arora 8. Physical and Geotechnical Properties of Soils, 1984. Joseph E. Bowles. 9. An Introduction of Geotechnical Engineering, 1982. R. D. Holtz and W. D. Kovacs. 10. Problem Solving in Soil Mechanics, 2003. A. Aysen. 11. Solving problems in Soil Mechanics, 1986. B. H. C. Sutton.

Course program

Month Week No. Description

Feb Week 1

Week 2

Week 3

Ch.1/Introduction, Definitions

Ch.2/ Volume Weight Relationship, Examples, H.W

Ch.3/ Soil description and classification, Soil Classification,

Soil Classification H.W - Quiz

Mar Week 4

Week 5 Week 6

Ch.4/ Compaction of soils, Laboratory compaction test, Field

compaction methods, CBR. H.W Ch.5/ Permeability Through Soils

Seepage Through Soils. H.W

Permeability and Seepage Through Soils Examples, Quiz

Seepage Control, Design Filter. H.W - Quiz

Apr Week 7

Week 8

Week 9

Week 10

Ch.6/Stresses within Soil Masses

Stresses within Soil Masses, Examples, H.W

Total and Effective Stresses, Types of Soil Water, Capillary

Rise Examples, H.W Quiz Ch.7/Shear Strength Parameters of Soils, Laboratory Tests

Direct shear, triaxial, unconfined compression tests, Stress path, Sensitivity and Thixotropy of Clay

Examples, H.W. Quiz

May Week 11

Week 12

Week 13

Week 14

Week 15

Ch.8/Compressibility and Consolidation of soil,

Coefficient of Compressibility, NCC, OCC, UCC, disturbance

The Degree of Consolidation, Coefficient of Consolidation

Examples, H.W. Quiz Ch.9/Slope Stability Slope Stability Examples Ch.10/Lateral Earth Pressure

Examples H.W.

Ch.11/Soil investigations