2-17
Advanced Soil Mechanics I
2.2 Rate-Independent Settlements
(1) Elastic Theory
B
qs (applied stress)
Deformation
pattern
Rigid
Flexible
For Df(=depth to the bottom of foundation level) = 0 and assuming soil
as an elastic material,
Si =
Immediate
Settl
1-65
Advanced Soil Mechanics I
2) Shearing Conditions
a) Anisotropy
1) Material Inherent anisotropy
2) K0 1 Stress system anisotropy
2 types
Caused by tendency of clay particles to become horizontally oriented
during deposition (1 D Compression)
Anisotro
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Advanced Soil Mechanics I
(3) SHANSEP (Charles C. Ladd (MIT)
Stress History and Normalized Soil Engineering Properties
Undrained shearing behaviors of clays can be represented by
'
normalized strength concept. ( su / vc = f(soil type & OCR)
Sample
2-1
Advanced Soil Mechanics I
Chapter II
Deformation Analysis
2.1 Stress Distribution in Soil
ex) What is settlement caused by embankment loading?
(Applied Stress) = h
B
= v ( stress induced by )
= h
v
H
1-D loading
h
If NC clays,
consolidation settle
2-100
Advanced Soil Mechanics I
* Modification of stress path method for settlement computation of
normally consolidated clays (Kim et al. (2011)
1) Gradual change of Poissons ratio during consolidation
Ex) Circular footing under uniform vertical loading
Advanced Soil Mechanics 1
Syllabus
This class deals with shear strength, deformation characteristics and
consolidation theory. The shearing behaviors of both cohesive soils and cohesionless
soils are discussed. The theories for settlement estimation in el
2-74
Advanced Soil Mechanics I
2.3 Rate Dependent Settlements
Time dependent settlement :
Primary consolidation : related to dissipation of ue
Secondary compression : relevant to drained creep (ue=0) at
constant vertical stress.
How to compute consolidati
Advanced Soil Mechanics I
2-38
(4) Stress Stress Behavior (Stiffness) of Soils.
Stress-Strain Behavior
depends on the composition, void ratio, stress history of the soil,
manner in which the stress applied, and so on.
describes based on the theory of el
2-88
Advanced Soil Mechanics I
Stress path method (Lambe 1964, 1967)
- Settlement estimation based on realistic deformation characteristics
measured from stress path tests which duplicate field stress paths and
probable deformation modes of soil elements.
Advanced Soil Mechanics I
2-113
2.4 Pore Pressure Developed during Undrained Loading
(1) Undrained Loading
Loading effects on soils can be divided into two phases;
i)
Undrained loading : Pore pressure is developed but there is no
flow of pore fluid.
ii) D
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Advanced Soil Mechanics I
Comments on Rate-Dependent Behavior of Soils
Assumptions on the theory of consolidation and their possible solutions
i) kv (or k h ) remains constant during consolidation.
Fig. 2-61 Changes in Permeability and compressibil
2-32
Advanced Soil Mechanics I
iv) CPT
Schmertmann(1970)
; modified later by Schemertmann and Hartman(1978)
Using strain influence factor (Iz)
Settlement =
z
dz
z =
p
Iz
Es
Iz = f(footing geometry, )
Fig. 2-13 and 2-14 in page 2-33 (based on theoretical,
1-13
Advanced Soil Mechanics I
(3) Stress Paths
Definition
Locus of maximum shear stress for any loading history
n
Lambs stress space
q=
1 3
p=
2
=
1 + 3
p=
'1 '3
2
q
2
'1 + '3
p
2
45 45
a
3
1
p, p
a
sin' = tan
c'cos' = a
SNU Geotechnical and Geoenviron
1-53
Advanced Soil Mechanics I
(2) Undrained Strength
Sophistication for selecting su
Triaxial or field tests
su
OC
su varies with depth and stress history
For truly N.C. clays,
su
'
po
=
su
'
vc
=
su
pc'
= const.
NC
Vertical consolidation stress
For t
1-33
Advanced Soil Mechanics I
(2) Shear Behavior of Sands (also clays)
Most important factors in determining shear strength itself (for given
soils).
i) Initial void ratio (density)
ii) Confining stress
Critical State cfw_
d v
dq
dp '
= 0, and
= 0 or
= 0
1-48
Advanced Soil Mechanics I
1.3 Shear Strength of Cohesive Soils
(1) Drained Strength
NC Clay
OC Clay
'
drained
=0
=0
UU behavior
su
UU behavior
su
n, n '
0.8 p 'c
n, n '
(max. past pressure)
Fundamental Shear Strength Parameters
- Hvoslev Parameter
Advanced Soil Mechanics I
1-59
b) K0 consolidation condition
In field
In lab
K0 state
Generally isotropic state (triaxial test) to simplify the field
conditions
< For sedimented soils>
Field : During sedimentation and subsequent loading (no lateral strain
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Advanced Soil Mechanics I
1.4 Special Soils
(1) Compacted clays (sandy clays or silty clays)
Unique characteristics
i.
Partially saturated
boundary pressures :
ii.
Dilatant at low pressures
15 20 psi
iii.
Contractive at moderate pressures
iv.
Highly
1-40
Advanced Soil Mechanics I
3) UU behavior
To run test
Apply a pressure to sample, con (For example, 1 atmosphere pressure),
so that sample can stand self-supported in TX cell.
Close drainage lines and apply cell pressure, cell .
Load sample to fail
Advanced Soil Mechanics I
1-1
Chapter I
Shear Strength of Soils
1.1 Background
(1)
Principal Stresses and Mohr Circle
Principal planes: Three orthogonal planes on which there are zero
shear stresses.
Principal stresses: The normal stresses that act on the