Unit Description and General Aims

The objective of presenting this unit is to impart to students the principles of soil mechanics, particularly soil behavior under mechanical loads and deformation upon interaction with water.

The subject matter covered in this unit will include: the formation of soils, as well as their characterization and classification; the principles of fluid mechanics and the determination of hydraulic conductivity; fundamental mechanical concepts such as the effective stress concept, strength of soils, consolidation, settlement, and testing procedures.

Upon concluding this unit, students will have acquired knowledge of the principles of soil mechanics and be able to develop mechanical models for soils. Such models are the pillars of a range of geotechnical engineering applications, such as the design of foundations, retaining walls, and dams.

Learning Outcomes

1. Explain the formation of soils, and interpret fundamental phase relationships for soils; determine particle size distribution; classify soil materials considering several soil classifications.
   Bloom's Level 5
2. Determine the flow of water through soils and explain their impacts on soil behavior; determine the hydraulic conductivity of soils based on lab and field data.
   Bloom's Level 5
3. Determine stresses and strain in soils, elastic settlement, and stress states using Mohr's circle theory.
   Bloom's Level 5
4. Explain the role of effective stress in geotechnical engineering.
   Bloom's Level 5
5. Determine and evaluate the acting stresses in a soil mass due to surface loads resulting from engineering constructions and applications.
   Bloom's Level 5
6. Interpret stresses and strain invariants, determine stress paths for common soil loadings, and explain the difference between total and effective stress paths.
   Bloom's Level 5
7. Analyze consolidation of soils based on related basic theory and testing methods.
   Bloom's Level 4
8. Analyze soils' shear behavior and strength based on basic theory and testing methods.
   Bloom's Level 4

Student Assessment

Overall Requirements: Students must achieve a result of 50% or above in the exam itself to pass the exam, and must pass the exam to be able to pass the unit. An overall final unit score of 50% or above must be achieved to pass the unit once all assessment, including the exam, has been completed.

Prescribed and Recommended Readings

Required textbook(s):

• Knappett, J. A., and Craig, R. F., 2019. Craig’s Soil Mechanics, 9th Edition. CRC Press - ISBN: 978-1138070066.

Reference Materials:

• Das, B.M., 2022. Principles of Geotechnical Engineering, SI version, 10th Edition. Cengage Learning - ISBN: 978-0357420485.
• Budhu, M., 2011. Soil Mechanics and Foundations, 3rd Edition, John Wiley & Sons, Inc., USA - ISBN: 978-0470556849.

Unit Content

Topic 1

Introduction – Basic Characteristics of Soils

• The origin and nature of soils
• Plasticity of fine-grained soils
• Particle size analysis
• Soil description and classification
• Phase relationships

Topic 2

One-Dimensional Flow of Water Through Soils

• Head and pressure variation in a fluid at rest
• Darcy’s law
• Empirical relationships for permeability
• Flow parallel and normal to soil layers
• Equivalent hydraulic conductivity
• Determination of the hydraulic conductivity
  • Constant head test
  • Falling-head test
  • Pumping test

Topic 3

Stresses and Strain

• Normal stresses and strains
• Idealised stress-strain response and yielding
• Hook’s law
• Plane strain and axisymmetric conditions
• Anisotropic, elastic states
• Stress and strain states

Topic 4

Total and Effective Stresses

• The principle of effective stress
• Numerical solution using the Finite Difference Method
• Response of effective stress to a change in total stress
• Stress in saturated soils without seepage
• Stress in saturated soils with downward and upward seepage
• Seepage force
• Effective stress in partially-saturated soils
• Capillary rise in soils
• Liquefaction

Topic 5

Stresses in Soil from Surface Loads (Part I)

• Normal and shear stresses on a plane
• The pole method of finding stresses
• Stresses caused by a point load
• Vertical stress caused by a horizontal line load
• Vertical stress caused by a vertical strip load
• Vertical stress caused by a horizontal strip load
• Linearly increasing vertical loading on an Infinite strip

Topic 6

Stresses in Soil from Surface Loads (Part II)

• Vertical stress due to embankment loading
• Vertical stress below the centre of a uniformly loaded circular area
• Vertical stress at any point below a uniformly loaded circular area
• Vertical stress caused by a rectangular load area
• Influence Chart for Vertical Pressure
• Westergaard’s Solution for Vertical Stress Due to a Point Load
• Stress Distribution for Westergaard Material

Topic 7

Stress Path

• Stress and strain invariants
  • Mean and deviatoric or shear stress
  • Volumetric and deviatoric strain
• Stress Paths
  • Basic concept
  • Plotting stress paths using stress invariants
  • Plotting stress paths using two-dimensional stress parameters

Topic 8

Consolidation (Part I)

• The oedometer test
• Estimating compression and swelling parameters from index tests
• Consolidation settlement
• Degree of consolidation
• Terzaghi’s theory of one-dimensional consolidation

Topic 9

Consolidation (Part II)

• Determination of coefficient of consolidation
• Secondary compression
• Numerical solution using the Finite Difference Method
• Correction for the construction period
• Vertical Drains
• Pre-loading

Topic 10

Soil Behaviour In Shear (Part I)

• An introduction to continuum mechanics
• Simple models of soil elasticity
• Simple models of soil plasticity
  • Soil as a frictional material
  • The Mohr-Coulomb model
  • Effect of drainage conditions on shear strength

Topic 11

Soil Behaviour In Shear (Part II)

• Laboratory shear tests
  • Direct shear tests
  • Triaxial tests
• Shear strength of coarse-grained soils
• Shear strength of saturated fine-grained soils
• The critical state framework
• Residual strength
• Estimating strength parameters from index tests

Topic 12

Unit Review

In the final week, students will have an opportunity to review the contents covered in the Unit. Opportunity will be provided to clarify any outstanding issues.

Software/Hardware Used

Software

• Software: Excel

• Version: latest

• Instructions:  N/A

• Additional resources or files: N/A

Hardware

• N/A

Unit Changes Based on Student Feedback