dynamic soil properties important
TRANSCRIPT
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Dynamic Soil Properties
Dynamic, cyclic, static differenceLow strain, high strain properties
2. Stress Conditions by Mohr Circle
Sign convention Fig. 6.1
Mohr Circle to explain the normal & shear stresses on a plane inclined at
angle, .
Eqs. 6.1, Fig. 6.2
Pole any line drawn thru the pole will intersect the Mohrs circle at a
point that describes the and on a plane parallel to that line
*Principal Plane, Principal Stresses
Major 1, minor = 3, intermediate 2
(usually 2= 3, assume)
Increase of shear stress
Mohrs circle grows (Fig. 6.4)
Rotation of principal stress axes.
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*Stress Paths
- Plotting the variation of the position of a single point on Mohr circle- p = (1+ 3)/2, q = (1- 3)/2
- effective stress paths
P` = 1' '
3 1 3 1 3( ) ( )
2 2 2
u uu p u
+ + += = =
q` = 1' '
3 1 3 1 3( ) ( )2 2 2
u u q
= = =
-Consolidation (K0-cond.) (AB)
v , h = const. (foundation
loading)
Axial comp.(AC)
v= const. h , (active cond.)
Lateral ext.(LE)
v , h= const. (excavation)
Axial ext.(AE)
v= const. h, (passive cond.)
lateral comp.(LC)
- Soil Element subjected to vertically propagating S-wave
change of Mohr circle
variation of Pole point rotation of principal axesvariation in stress paths
not considered in the lab. And field tests
p
3 1
ACLE
A
B
AELC
q
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Ch. 6 Behaviors of SoilsUnder Static and Dynamic L
Deformational Characteristics of Soils
or )
G1 or E2)G2 or E2)
0.1 0.2
Stress-Strain RelationshipStress-Strain Relationship
G (or E)
0.001 0.
Modulus-Strain RelatiModulus-Strain Relatio
(ora), %
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Deformational Characteristics of S
Intermediate sSmall strains (
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Dynamic Soil Properties
Dynamic Modulus : Youngs Modulus(E), Shear MConstraint Modulus(M)
Poissons Ratio() Damping Ratio(D) and attenuation coefficient(
Liquefaction Resistance and Shear Strength with
-> Apply to Dynamic AnalysisSoil-Structure Interaction Analysis
In-situ Seismic Test Crosshole, Downhole, SASW, HWAW, Refract Vs -> Gmax
Laboratory Test Cyclic TX, RC/TS, Simple shear test, Shaking G-log , D-log Liquefaction Potential
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Static, Cyclic, Dynamic Soil Propert
Modulus by Testing Condition
Strain
Stress Load
Strain
Stress Loa yclic Modulus- cyclic loading(low frequency)
- Cyclic TX, Torsion shear
Static Modulus- monotonic loading- Triaxial Tests etc..
Dynamic Modulus- cyclic loading
(high frequency)- Resonant Column etc..
Loa Inertia plays role
In the past, Gstatic GdynamicIn the past, Gstatic Gdynamic
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Measurement of Dynamic Soil Properties
*Measurement of low-strain properties wave propagation*Measurement of large-strain properties stress-strain
*Selection
Replicate the initial stress conditions
Replicate the anticipated cyclic loading conditions.
*Dynamic Soil Properties and Stress-strain Ralationhand out
*Source of uncertainty
Inherent variability
Inherent anisotropy(soil structure)
Inherent anisotropy(by stress conds)
Disturbance
Limits of testing equipments
Testing and interpretation errors
1. Field Tests
Advantage : not requiring sampling
Response of relatively large Volume of soil
Including similar soil deformation to real problems
Disdvantage : can not represent other conditions
Not control drainage
Properties obtained indirectly
(theoretically, correalations)
Surface Test. Vs. Borehole Test
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1.1. Low-strain Tests
Strains below 0.001%Based on elastic wave propagation(body wave, R wave)
P-wave : fastest
S-wave : using polarity characteristics
Averaging technique
Effects of Ground water
(a)Seismic Reflection Test
Determine V and H of surficial layers
H, Vp1
Vp2
2H/vp1
1/vp
S x R
t
x
Direct arrival
td= x/vp1
Reflected arrival
tr=2 2
1
4
p
H x
V
+ H = 2 2 2
1
1
2 r pt V x
Or use intersection
Inclined layer boundary
Difficulties of determining arrival time tr
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Seismic Refraction Test
using the arrival times of the first waves (P or S)
typical test setup
Horizontal Layering
direct arrival 1/ vxt nd = Snells Law
At the boundary reflect, refract Huygens Principal
- 36 -
critical angle of incident( )Ci
refracted wave parallel to the boundary
produce head wave
near source receiver dist. direct arrival first far dist. After critical distance head wave first
Cx
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1/1 v
2/1 v
12
12
2 vvvvxH c
+
=
1
2
v
iHCosC
dist.
Cx
For multi layers Fig. 6.14.
Basic Assumptions : Velocity increases w depth
2
1
21
90
v
viSin
v
Sin
v
iSinC
C==
o
* Inclined or Irregular Layering p 106~111 (Richart et. al)
* Example
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