CIEG 320: Soil Mechanics

Fall Semester 2013

Instructor: Victor N. Kaliakin

Department of Civil & Environmental Engineering

University of Delaware

voice: 302.831.2409 ; FAX: 302.831.3640 ; e-mail

- Discussion of Class Syllabus (available as a PDF file ).
- Introductory remarks pertaining to soil mechanics and geotechnical engineering (
**associated reading**: Chapter 1 in textbook).

- Origin of soil (
**associated reading**: Chapter 3 in textbook).- Definition of Geology & Geological Engineer
- The Earth: core, mantle, crust. Lithosphere.
- Brief overview of minerals.
- Rocks: igneous, sedimentary, metamorphic.
- Definition of soil.
- Weathering: physical, chemical, solution.

- Nature of soil.
- Weight-Volume Relationships (
**associated reading**: Sections 2.1 to 2.3 in textbook).- Definition of mass densities (
**associated reading**: Section 2.1 in textbook). - Definition of unit weights (
**associated reading**: Section 2.3.2 in textbook). - Specific gravity (
**associated reading**: Section 2.3.2 in textbook). - Definition of porosity, void ratio, water content, degree of saturation (
**associated reading**: Section 2.2 in textbook). - Relationship between unit weight, void ratio, moisture content and specific gravity.

- Definition of mass densities (

- Office hours announced:
- Mondays: 9:30 - 11:00 a.m. and 2:00 - 4:00 p.m. (Meysam)
- Wednesdays: 10:00 a.m. - noon (Meysam); 3:00 - 5:00 p.m. (VNK)
- Fridays: 10:00 a.m. - noon (Meysam)
- TuTh: 9:30 - 11:00 a.m. (Meysam); 3:30 - 5:00 p.m. (VNK)
- or by appointment. (Meysam's e-mail: meysam@udel.edu; he will hold his office hours in Rooms 285/286 in P.S. DuPont Hall).

- Weight-Volume Relationships (continued).
- Two example problems solved.

- Homework Assignment #2 assigned, due 09-12-13.

- Weight-Volume Relationships (continued).
- Derivation of buoyant unit weight.

- Index properties.
- Role of classification tests.
- Overview of soil particle shapes and microfabric of clays ( PPT file ).

- Particle-size distribution (
**associated reading**: Section 2.5 in textbook). - Homework Assignment #3 assigned, due 09-19-13.

- More detailed description of soil types.
- Cohesionless (gravels, sands, silts).
- Cohesive (clays).
- Coarse-grained (gravels & sands) and fine-grained (silts & clays).

- Particle-size distribution (continued).

- Quantification of the Plasticity of Soil: the Atterberg Limits (
**associated reading**: Section 2.7 in textbook).- General comments pertaining to characterization of fine-grained soils (i.e., silts and clays).
- Liquid limit.
- Plastic limit.
- Shrinkage limit.

- Derived Quantities
- Plasticity index.
- Liquidity index.

- Calculation of shrinkage limit from typical known values.

- NOTE: the first 75-minute examination will be administered on Thursday, October 10, 2013.
- Soil Compaction (
**associated reading**: Chapter 5 in textbook).- Fundamental definition of compaction.
- Benefits of compaction?
- Mechanics of densification: a) In
*cohesionless*soil; b) In*cohesive*soil. - Key quantities in soil compaction: moisture content; dry density.
- Hypothetical field experiment to determine optimal water content.
- Optimal water content; maximum dry unit weight (
**associated reading**: Section 5.3 in textbook).

- Homework Assignment #4 assigned, due 10-01-13.

- Soil Compaction (continued).
- Zero air voids curve.
- Relative compaction.
- Relative density and associated derivations (
**associated reading**: Section 5.5.1 in textbook). - Example problem.

- Hydrostatic water in soils and rocks
- Capillary rise in soils (
**associated reading**: Section 6.2 in textbook). - Groundwater table, capillary zone, vadose zone (
**associated reading**: Section 6.3 in textbook). - In Situ Stresses (
**associated reading**: Section 6.9 in textbook).- Total stress (example of a saturated soil deposit).
- Pore fluid pressure.
- Definition of effective stress.

- Capillary rise in soils (

**RECALL:**75-minute exam #1 will be administered on Thursday October 10, 2013, from 2:00 to 3:15 p.m. in Room 004 Kirkbride.- Closed book/closed notes.
- One double-sided (8.5 by 11 inch) page of notes permitted & must be turned in with the exam.
- The exam will cover appropriate sections of Chapters 1 to 5.
- Since homework was not assigned in Chapters 1, 3 & 4, only relatively general aspects from these chapters will be tested as part of the short-answer portion of the test (see next item).
- The exam will contain 5 to 8 short-answer questions that will be very
*general*in nature. - The exam will not contain numerical problems related to Atterberg limits - these will be addressed in the CIEG 323 final exam.
- Bring paper and a straight edge (any type of graph paper will be provided if needed).

- In Situ Stresses (continued).
- Vertical stress profiles (
**associated reading**: Section 6.10 in textbook) with detailed example that includes capillary rise. - Relationship between horizontal and vertical stresses (
**associated reading**: Section 6.11 in textbook).

- Vertical stress profiles (

- Review problems for 75-minute exam #1.

- 75-minute exam #1.

- Fluid Flow in Soils and Rock.
- Motivation for studying flow through soils.
- Assumptions related to flow through soils: 1) laminar, 2) incompressible flow.
- Law of conservation of mass and its simplification in light of the assumption of an incompressible fluid.
- Bernoulli energy equation; total hydraulic head (
**associated reading**: Sections 7.2 and 7.5 in textbook). - Seepage velocity (
**associated reading**: Section 7.2 in textbook). - Darcy's law; hydraulic conductivity; coefficient of permeability (
**associated reading**: Sections 7.3 and 7.4 in textbook).

- 75-minute examination #1.
- Solution to this exam ( PDF file ).
- Average: 82.5/125 (66.0%). Range: 27.5 to 124.5.

- One-Dimensional Fluid Flow in Soils - with hand-out (
**associated reading**: Section 7.5 in textbook).- Hydrostatic state of stress.
- Saturated soil with upward seepage.
- Critical gradient (
**associated reading**: Section 7.6 in textbook). - Saturated soil with downward seepage.

- NOTE: the second 75-minute exam shall be given on Thursday, November 7, 2013.
- Brief review of Bernoulli's equation, Darcy's law and one-dimensional flow through soils.
- Two-Dimensional Seepage.
- General assumptions (steady-state flow; saturated soil; no change in void ratio, implying no volume change of the soil mass).
- Flow lines; equipotential lines; flow nets (
**associated reading**: Section 7.7 in textbook). - Example consisting of one-dimensional flow: solved using Darcy's law and then again using the equations associated with flow nets.

- One-dimensional seepage example (Problem 7.14, Case II).
- Effect of varying the location of the datum on the elevation and total head.
- Computation of total stress, pore pressure and effective stresses at various points in the soil sample.
- General comments regarding the computation of Darcy velocity and seepage velocity.

- Equation governing two-dimensional steady-state seepage.

- Compressibility of Soils (
**associated reading**: Chapter 8 in textbook).- General comments pertaining to deformations and strains in soils.
- Overview of settlement of soils.
- Components of settlement (
**associated reading**: Section 8.2 in textbook). - Elastic settlement (
**associated reading**: Section 8.2 in textbook). - Primary consolidation settlement (
**associated reading**: Section 8.3 in textbook). - One-dimensional laboratory consolidation test (
**associated reading**: Section 8.4 in textbook). - Void ratio vs. effective stress plots (
**associated reading**: Section 8.4 in textbook). - Normally consolidated & overconsolidated clays (
**associated reading**: Section 8.5 in textbook).

- Compressibility of Soils (continued).
- Primary consolidation settlement (
**associated reading**: Section 8.3 in textbook). - One-dimensional laboratory consolidation test (
**associated reading**: Section 8.4 in textbook). - Void ratio vs. effective stress plots (
**associated reading**: Section 8.4 in textbook). - Compression index (Cc) and swell/re-compression index (Cr).
- Settlement cases involving normally consolidated & overconsolidated clays (
**associated reading**: Section 8.5 in textbook). - Example problem: computation of primary consolidation settlement ( PDF file ).

- Primary consolidation settlement (

- Review problems for 75-minute exam #2.

- 75-minute exam #2.

- Time Rate of Consolidation (
**associated reading**: Section 9.3 in textbook).- Assumptions underlying Terzaghi's theory of one-dimensional consolidation.
- The consolidating layer is horizontal, of infinite extent laterally and of constant thickness.
- Throughout the consolidating layer the soil is homogeneous and is completely saturated (i.e., it is a two-phase material - no air is present in the pores).
- Due to the above homogeneity, the constitutive relations and permeability do not vary spatially or with time.
- Compared to the soil mass as a whole, the compressibility of the soil grains and of the pore fluid is negligible (i.e., several orders of magnitude lower). This implies that the deformation of the soil mass is due entirely to changes in volume which result due to the forcing out of free fluid from the pores.
- The load is applied in only one direction and remains constant for
all time. Thus, since the total stress is given, if the
pore pressure
*u*is computed, the effective stress will be determined from the usual effective stress equation. - Deformation occurs only in the direction of load application; i.e., the soil is restrained against lateral deformation.
- The time rate of consolidation depends only upon the low permeability of the soil; viscoelastic properties of the soil skeleton are not considered.
- During consolidation the pore fluid flows only in the direction of load application; the free surface boundary offers no resistance to the flow of pore fluid from the soil.
- The flow of pore fluid is described by Darcy's Law; i.e., the flow is proportional to the gradient of pore pressure. The coefficient of permeability is assumed to remain constant (recall the third assumption above).
- The strains in the soil skeleton are controlled by the effective stresses, with a linear constitutive relation.
- Strain, displacement, velocity and stress increments are assumed to be small. As a result, the change in thickness of the consolidating layer is negligible.
- Inertia terms are neglected; i.e., a static analysis is assumed.

- Derivation of governing differential equation.
- Introduction of quantities associated with the governing differential equation.
- Coefficient of compressibility (a_v).
- Coefficient of volume compressibility (m_v).
- Coefficient of consolidation (c_v).

- Solution of the governing differential equation (using separation of variables).
- Definition of degree of 1-d consolidation (U_z).

- Assumptions underlying Terzaghi's theory of one-dimensional consolidation.

- Time Rate of Consolidation (continued).
- Overview of the governing differential equation and coefficient of compressibility (a_v), coefficient of volume compressibility (m_v), and coefficient of consolidation (c_v).
- Two example problems.

- Homework Assignment #8 assigned, due 11-26-13.

- 75-minute examination #2.
- Shear Strength of Soil (
**associated reading**: Chapter 11 in textbook).- Background information.
- Definition of strength.
- State of stress at a point (
**associated reading**: Section 11.1 in textbook). - Transformation of stresses under plane stress conditions.
- Principal stresses.
- Mohr's circle.
- Example problem.

- Background information.

- Shear Strength of Soil (
**associated reading**: Chapter 11 in textbook).- Example problem (in detail).
- Direct shear test and frictional nature of soil.

- Failure Criteria (
**associated reading**: Section 11.4 in textbook).- Mohr failure criterion (
**associated reading**: Section 11.4.1 in textbook). - Mohr-Coulomb failure criterion (
**associated reading**: Section 11.4.2 in textbook).

- Mohr failure criterion (

- Review for final examination.
- The final examination will be administered on Thursday December 12, 2013, from 1:00 to 3:00 p.m. in Room 004 Kirkbride.
- Closed book/closed notes.
- One double-sided (8.5 by 11 inch) page of notes permitted & must be turned in with the exam.
- Bring paper and a straight edge (any type of graph paper will be provided if needed).
- The final exam will contain general short-answer questions emphasizing material covered since the second 75-minute exam.
- The exam will cover appropriate sections of Chapters 7, 8, 9 and 11. In particular,
- Chapter 7: know general aspects of 2-d seepage (more for the short-answer portion of the exam). You will not have to draw flow nets on the final exam.
- Chapter 8: compressibility of soils (normally consolidated; overconsolidated; C_c, C_r, etc.).
- Chapter 9: time rate of consolidation (c_v, T, U_z, H_dr, etc.). If needed, consolidation charts will be provided.
- Chapter 11: stress transformations, including principal stresses and maximum in-plane shear stress. Know Mohr's circle associated with a particular state of stress. You will not have to draw Mohr's circles on the final.

- Notes regarding homework assignments
- Homework assignment #7 has been graded and was returned today.
- Once homework assignment #8 is graded a note will be posted on Sakai.
- All homework solutions are available on line via Sakai.

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Revision Date: 03.12.13