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Notes of Geotechnical Engineering
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LECTURE NOTEADVANCED SOIL MECHANICS
FIRST SEMESTER
M.TECH (GTE)
Dr. Debabrata Giri, Associate Professor
Department of Civil Engineering
Veer Surendra Sai University of Technology, Burla
Email: dgiri_ce@vssut.ac.in
1
,DISCLAIMER
These lecture notes are being prepared and printed for the use in training
the students. No commercial use of these notes is permitted and copies
of these will not be offered for sale in any manner. The readers are
encouraged to provide written feedbacks for improvement of course
materials.
Dr. Debabrata Giri
2
, COURSE CONTENTS
Module-I
Compressibility of soils: consolidation theory (one, two, and three dimensional
consolidation theories), consolidation in layered soil and consolidation for time dependent
loading, determination of coefficient of consolidation (Casagrande method and Taylors
method)
Module-II
Strength behavior of soils; Mohr Circle of Stress; UU, CU, CD tests, drained and
undrained behavior of sand and clay, significance of pore pressure parameters; determination
of shear strength of soil; Interpretation of triaxial test results.
Module-III
Stress path; Drained and undrained stress path; Stress path with respect to different
initial state of the soil; Stress path for different practical situations.
Module-IV
Elastic and plastic deformations: elastic wall; introduction to yielding and hardening; yield
curve and yield surface, associated and non-associated flow rule, Failure theories and
constitutive modelling.
Module-V
Critical state soil mechanics; Critical state parameters; Critical state for normally
consolidated and over consolidated soil; Significance of Roscoe and Hvorslev state boundary
surface; drained and un drained plane. Critical void ratio; effect of dilation in sands; different
dilation-models.
Reference Books:
Atkinson, J.H. and Bransby, P.L, The Mechanics of Soils: An introduction to Critical soil
mechanics, McGraw Hill, 1978.
Atkinson J.H, An introduction to the Mechanics of soils and Foundation, McGraw- Hill Co.,
1993.
Das, B.M., Advanced Soil Mechanics, Taylor and Francis, 2nd Edition, 1997.
Wood, D.M., Soil Behavior and Critical State Soil Mechanics, Cambridge University Press,
1990.
Craig, R.F., Soil Mechanics, Van Nostrand Reinhold Co. Ltd., 1987.
Terzaghi, K., and Peck, R.B., Soil Mechanics in Engineering Practice, John Wiley & Sons,
1967.
Lambe, T.W. and Whitman, R.V., Soil Mechanics, John Wiley & Sons, 1979
COURSE OUTCOME
1. The students obtain knowledge on compressibility parameters of soil mass.
2. The students are able to select the shear strength to design different structures for
different conditions of loading, drainage and failure criteria.
3. The students can estimate the stress path in soil under drainage condition.
4. The students can describe the mathematical models for solving different problems in
soil mechanics.
5. The students can illustrate the deformation behavior of soil mass.
3
, 1.0 Consolidation and Compression of Soils
When a soil layer is subjected to vertical stress, volume change can take place through
rearrangement of soil grains, and some amount of grain fracture may also take place. The volume
of soil grains remains constant, so change in total volume is due to change in volume of water. In
saturated soils, this can happen only if water is pushed out of the voids. The movement of water
takes time and is controlled by the permeability of the soil and the locations of free draining
boundary surfaces.
It is necessary to determine both the magnitude of volume change (or the settlement) and the
time required for the volume change to occur. The magnitude of settlement is dependent on the
magnitude of applied stress, thickness of the soil layer, and the compressibility of the soil.
When soil is loaded undrained, the pore pressure increases. As the excess pore pressure
dissipates and water leaves the soil, settlement takes place. This process takes time, and the rate
of settlement decreases over time. In coarse soils (sands and gravels), volume change occurs
immediately as pore pressures are dissipated rapidly due to high permeability. In fine soils (silts
and clays), slow seepage occurs due to low permeability.
Elastic settlement is on account of change in shape at constant volume, i.e. due to vertical
compression and lateral expansion. Primary consolidation (or simply consolidation) is on
account of flow of water from the voids, and is a function of the permeability and
compressibility of soil. Secondary compression is on account of creep-like behaviour.
Primary consolidation is the major component and it can be reasonably estimated. A general
theory for consolidation, incorporating three-dimensional flow is complicated and only
applicable to a very limited range of problems in geotechnical engineering. For the vast majority
of practical settlement problems, it is sufficient to consider that both seepage and strain take
place in one direction only, as one-dimensional consolidation in the vertical direction.
1.1 Compressibility Characteristics
Soils are often subjected to uniform loading over large areas, such as from wide foundations, fills
or embankments. Under such conditions, the soil which is remote from the edges of the loaded
area undergoes vertical strain, but no horizontal strain. Thus, the settlement occurs only in one-
dimension.
The compressibility of soils under one-dimensional compression can be described from the
decrease in the volume of voids with the increase of effective stress. This relation of void ratio
and effective stress can be depicted either as an arithmetic plot or a semi-log plot.
4
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