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Figure 4.12: Post Volumetric Shear Strain for Clean Sands (Ishihara and Yoshimine 1992)
The method for estimating the volumetric strain due to cyclic loading illustrated in Figure 4.12 is
based on laboratory data from cyclic triaxial tests. In order to evaluate the suitability of the
method for silts, the results of several laboratory investigations of Columbia River and Puget
Sound soils (Dickenson and Brown 1997a, 1997b) have been superimposed on the basic chart.
Data corresponding to high quality field specimens of non-plastic silt are plotted in Figure
4.13(a) and data obtained on reconstituted specimens of non-plastic silt and silt of moderate
plasticity (the PI of the Adair silt and Corvallis silt specimens is 10) are provided in Figure
4.13(b). The laboratory testing of these silts demonstrates that they exhibit post-cyclic loading
volume change that is similar to that of loose- to medium-dense sand. It appears, based on this
very limited data, that the method of Ishihara and Yoshimine (1992) can be used to estimate
settlements due to seismic loading of non-plastic to low-plasticity silt.
The procedure for estimating of soil densification and related settlements developed by
Tokimatsu and Seed (1987) can be used for saturated or nearly saturated soils, and for nonsaturated
soils. The Tokimatsu and Seed method proceeds in steps that are very similar to those
prescribed by Ishihara and Yoshimine (1992). The liquefaction susceptibility is again performed
for each loose- to medium-dense cohesionless soil layer, using simplified procedures described
in Chapter 3. For each soil layer or sub-layer, a representative estimate of (N 1 ) 60 and CSR eq are
required. Given this information, the volumetric strain can be estimated from the chart of CSR eq
(or τ av / σ o ′ as indicated in the figure) versus (N 1 ) 60 , as presented in Figure 4.14.
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