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Semester 2

Geotechnical Engineering 3 (CIVE09016)

Subject

Civil Engineering

College

SCE

Credits

20

Normal Year Taken

3

Delivery Session Year

2023/2024

Pre-requisites

2nd year undergraduate Soil Mechanics/Geomechanics/Geotechnical Engineering or similar

Course Summary

In this course, students develop further understanding of soil mechanical concepts and learn to apply them to solve geotechnical engineering problems. The course is a continuation of the second year soil mechanics module and extends the student's understanding of the mechanics of soils to include consolidation and shear failure of soil systems.

Course Description

LECTURESL1 Course introductionAspects of geotechnical design, structure of the course, course content, references with comments, revision on effective stress concept.L2 Stress distribution in soils 1In-situ stresses (revision), stress history, lateral stress ratio, normal and over-consolidation, overconsolidation ratio, factors affecting the induced stresses due to applied loads.L3 Stress distribution in soils 2Flexible and rigid footing on cohesive and cohesionless soils, Boussinesq elastic solution of point load at the surface, worked example.L4 Stress distribution in soils 3Boussinesq elastic solutions of induced soil stresses due to uniform pressure on a circular area, rectangular area and infinite strip, worked example.L5 Stress distribution in soils 4Newmark chart, worked example, Westergaard theory, approximate method, bulb of pressure.L6 Shear strength 1Revision on total and effective stress Mohr's circles, Mohr-Coulomb failure criterion, experimental failure envelope, cohesion and internal friction angle.L7 Shear strength 2Other useful forms of the Mohr-Coulomb equation, worked example, stress parameters: (tau, sigma), (sigma_1, sigma_3), (t, s), (p, q) and applications.L8 Shear strength 3 : laboratory measurement of strengthDirect shear: tester, testing procedure, advantages and limitationsTriaxial testing: tester, testing procedure, consolidation stage, volume measurement, pore water pressure measurement, triaxial compression and triaxial extension.L9 Shear strength 4 : common types of triaxial testingUnconsolidated-undrained (UU) test, unconfined compression test, consolidated-undrained test (CU), consolidated-drained test (CD).L10 Shear strength 5 : triaxial test analysis IUndrained shear strength parameters and effective shear strength parameters, analysis of triaxial test results, worked example.L11 Shear strength 6 : triaxial test analysis IIUndrained shear strength parameters and effective shear strength parameters, analysis of triaxial test results, worked example.L12 Shear strength 7Mechanisms of shearing and straining. Mechanical behaviour of sands. Response of deviator stress and volumetric strain under axial straining, critical void ratio, residual strength, angle of repose.L13 Shear strength 8 Mechanical behaviour of clays. Response in drained and undrained tests for normally consolidated andoverconsolidated clays, sensitivity of clays.L14 Shear strength 9Pore pressure parameters. Skempton pwp parameters A and B, range of values of the parameters for different clays, worked example. Comments on laboratory sessions 1 and 2 on shear strength measurements. Comments on Laboratory Sessions 1 & 2 on the triaxial test results. L15 Consolidation and settlement 1Consolidation vs compression, important questions: magnitude and rate of settlement, piston-spring analogy, oedometer test, undisturbed sample.L16 Consolidation and settlement 2Useful parameters from oedometer test: coefficient of compressibility av, coefficient of volume compressibility mv, compression and swelling indices Cc and Cs, empirical relation on Cc, worked example.L17 Consolidation and settlement 3Preconsolidation pressure, causes of overconsolidation, graphical procedure for determining preconsolidation pressure.L18 Consolidation and settlement 4Terzaghi theory of one-dimensional consolidation, hydrostatic and excess pore water pressure (pwp), isochrones of excess pwp at various stages, assumptions, derivation.L19 Consolidation and settlement 5Solutions to the consolidation differential equation, boundary conditions and initial conditions, average degree of consolidation for a clay stratum, local degree of consolidation, worked example.L20 Consolidation and settlement 6Comparison of experimental and theoretical consolidation curves, determination of coefficient of consolidation cv from oedometer test: square-root time method.L21 Consolidation and settlement 7Determination of coefficient of consolidation cv from oedometer test: log-time method, determination of permeability k from oedometer test results. Comments on the oedometer test simulation exercise. L22 Lateral pressures and retaining structures 1Pressures at Ko and limiting equilibrium states, assumptions in earth pressure theory, Rankine theory of active and passive earth pressures.L23 Lateral pressures and retaining structures 2Direction of failure planes, surcharge on backfill, deformations to mobilise active and passive states, active and passive pressure distribution.L24 Lateral pressures and retaining structures 3Calculation of wall loads, total and effective stress analysis, worked example.L25 Lateral pressures and retaining structures 4Coulomb theory of earth pressures, types and designs of retaining wall.L26 Lateral pressures and retaining structures 5Further work example. Coulomb theory of earth pressures. Types and designs of retaining wall.L27 Bearing capacity of shallow foundations 1Adequate factor of safety against shear failure in shallow foundations, loadingresponse of shallow foundations, bearing capacity theories and equation, strip, square and circular footings.L28 Bearing capacity of shallow foundations 2Bearing capacity terms and definitions, footings on clays, footings on sands. Work example.L29 Bearing capacity of shallow foundations 3Eccentric and inclined loads, worked example.L30 Bearing capacity of shallow foundations 4Further worked example and concluding remarks.L31 Slope stability 1Introduction to slope stability. Cuttings and embankments. Translational sliding. Worked example.L32 Slope stability 2Infinite slope and frictional material. u = 0 analysis. Taylor's curves.L33 Slope stability 3Bishop's method of slices, interslice forces, concluding remarks.L34 Summary and concluding remarksRecap on the main aspects of foundation design and the topics covered in this course, total stress (undrained) analysis vs effective stress (drained) analysis.PROBLEM SOLVING SESSIONSThe aim is to give the students ample opportunities to develop skills in problem solving, to apply the theories and methods learned in the course to common geotechnical engineering situations. The exercises cover a variety of geotechnical problems in varying degrees of difficulty.Session 1: Stress distributions in soilsThis session is intended for students to develop skills in calculating the induced stresses in soils due to applied loadings for a variety of situations, including footings of different shapes embedded at different depths.Session 2: Shear strengthThis session is intended for students to develop skills in solving geotechnical problems which require shear strength calculations, including drained and undrained failure properties, analysis of laboratory test results to evaluate the failure stresses and failure properties, total and effective stress paths and calculations involving pwp parameters.Session 3: Consolidation and settlementThis session is intended for developing skills in performing consolidation settlement analyses. The magnitude of settlement and the time taken to reach a certain degree of consolidation are being evaluated for many geotechnical situations.Session 4: Lateral earth pressuresThis session is intended for developing skills in solving geotechnical problems which require lateral earth pressure calculations. Session 5: Bearing capacity in shallow foundationsThis session is intended for developing skills in performing bearing capacity calculations for various types of footing.Session 6: Slope stabilityThis session is intended for developing skills in performing slope stability analyses including use of Taylor's curves and Bishop's method of slices.LABORATORIESThe students work in groups under the supervision of a laboratory demonstrator, analyse the results and submit laboratory reports for assessment. The aim is to train the students to carry out triaxial tests, including the analysis of the test results and the evaluation of the relevant properties. An analysis of simulated oedometer test data will also be carried out.Laboratory Session 1 UU testing of clayThe undrained shear strength characteristics of a clay are investigated by UU tests. Each group of students will learn about sample preparation and testing in a triaxial machine. Sample data and testing data are to be recorded in the data sheets. A brief report is to be submitted for assessment.Laboratory Session 2 Consolidated-undrained testing of clayThe total and effective stress shear strength characteristics of a clay are investigated by CU tests. Every group of students will learn about sample preparation and testing in a triaxial machine. Sample data and testing data are to be recorded in the data sheets. Each group is to carry out one CU test and the results from all groups are then pooled and analysed. A full report is to be submitted for assessment.Laboratory 3 Oedometer testing of clayThe consolidation and compression properties of a cohesive soil are investigated using an oedometer test. The students will first learn about conducting an oedometer test. They will then analyse the test data to derive the relevant compression and consolidation properties of the clay.

Assessment Information

Written Exam 70%, Coursework 30%, Practical Exam 0%

Additional Assessment Information

Intermittent Assessment: 30%Degree Examination: 70%

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