Geoscience Reference
In-Depth Information
120
Vaid & Sivathayalan (1996)
Frazer Rivers and, water pluviated
Undrained direct simple shear tests
σ vc = 200 kPa
D R = 52%
80
D R = 43%
D R = 35%
40
D R = 31%
Shear resistance at
phase transformation
0
0
4
8
12
16
20
Shear Strain (%)
Fig. 1.6. Undrained direct simple shear testsonFraser river sand at a range of relative
densities byVaid and Sivathayalan (1996)
river sand by Vaid and Sivathayalan (1996). The bullet symbols on this figure identify
pointsofminimumshearresistancewhichcorrespondtothetransitionfromanincremen-
tally contractive to an incrementally dilative response in undrained shearing (i.e., phase
transformation)andwhichhavealsobeencalledaquasi-steadystatecondition(Ishihara,
1993). The monotonic shear resistance can increase significantly after phase transfor-
mation, with the rate of increase being greater for a higher initial D R . The normalized
shear resistance,
τ / σ vo , for this sand at
σ vo of 50 to 400kPa are plotted versus D R in
τ / σ vo at phase transformation is relatively independent of
Figure 1.7, showing that: (1)
σ vo for
τ / σ vo increases with both increasing
D R and increasing shear strainbeyond phase transformation.
The values of
σ vo ranging from 50 to 400kPa, and (1)
τ / σ vo mobilized at quasi-steady state or at shear strains of 5 to 20%
increase rapidly as D R exceeds about 40 to 50%. This is illustrated by the results in
Figure 1.8 for undrained simple shear loading of saturated Toyoura sand at
σ vo of 50
to 300kPa by Yoshimine et al. (1999), as well as by the previously discussed results
for Fraser river sand in Figure 1.7. The trends in Figures 1.7 and 1.8 suggest that the
undrained shear strengths of these sands at
σ vo less than 400kPa would exceed their
τ / σ vo =
φ
drained strengths (e.g.,
6) for D R greater than 50 to60%.
The potential for void redistribution to cause localized loosening and strength loss in the
field depends on numerous factors, including the initial state and properties of the soil
(e.g., cyclic strength, D R , confining stress), the geometry and boundary conditions for
tan
0
.
 
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