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Behavior of Soft Clays in Direct Simple
Shear
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The key element for a realistic prediction of cyclic clay behavior is the implementation of an accurate stress-strain-strength
relationship, which incorporates the effect of previous consolidation stress history, soil nonlinearity and the
generation of excess pore pressures and accumulation of strains during irregular cyclic shearing.
The presence of an initial consolidation shear stress (i.e. a slope) has a considerable influence on the behavior
of soft, cohesive normally consolidated soils measured in the laboratory both in monotonic and cyclic simple shear
tests. During monotonic loading higher consolidation shear stress causes the response to become more brittle, the
peak to shift to lower strain levels and the additional stress to the maximum to decrease. This implies that a
lower amount of stress and strain needs to be mobilized for the specimen to reach potentially unstable consitions.
During cyclic loading, the presence of an initial shear stress forces the average shear strain to increase, shifting
the stress-strain loops away from zero.
A new simplified effective-stress-based model, called SIMPLE DSS, was developed to describe the response of this
type of soils for the use in seismic site response analysis. SIMPLE DSS is a simplified effective stress model
specifically developed for simple shear stress conditions. It is based on an effective stress formulation that
allows the simulation of monotonic and cyclic simple shear tests on normally consolidated (NC) to lightly overconsolidated
clays. A total of five parameters are needed to simulate monotonic tests and another two describe the behavior
during cyclic loading. |
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| Prediction of a cyclic direct simple shear test using SIMPLE DSS. |
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