Abstract
Past studies revealed that excess pore pressure generation due to cyclic loading is highly governed by induced strains, volumetric deformation potential of soil, number of cycles, and bulk stiffness of pore fluid. It is well established that partial saturation can significantly reduce bulk stiffness of pore fluid and consequently excess pore pressure generation during seismic loading. On the basis of that, a number of researchers have investigated induced partial saturation as an effective soil improvement technique to increase the liquefaction resistance of fully saturated soils. This paper focuses on development of a semi- empirical model to interpret the effects of partial saturation on the excess pore pressure generation in sands. In this regard, an existing strain based excess pore pressure ratio (ru) prediction model originally developed for fully saturated soils was modified to incorporate the effect of partial saturation on the excess pore pressure generation. The literature data as well as data from a series of strain-controlled direct simple shear test were used to evaluate the reliability of the proposed equation in predicting the excess pore pressure ratio in partial saturation condition.
Highlights
Seismic loadings such as earthquakes induce cyclic shear strains resulting in rearrangement and densification of soils to a more stable condition
Experimental results from undrained strain-controlled Direct Simple Shear (DSS) tests are presented in terms of excess pore pressure ratio with induced shear strain
The results indicate that the threshold shear strain falls between 0.005 and 0.025%
Summary
Seismic loadings such as earthquakes induce cyclic shear strains resulting in rearrangement and densification of soils to a more stable condition. Because the pore space of saturated soils is filled with a relatively incompressible fluid like water, the pore fluid resists against densification under an undrained condition, which leads to pore pressure build-up. This generation of pore pressure is the main mechanism in seismically induced liquefaction. Previous research indicated that the excess pore pressure generation (∆u) is mainly governed by induced volumetric strains and soil and fluid stiffness characteristics, and can be estimated using the following equation [5, 7, 8]:. The literature data as well as data from a series of strain-controlled direct simple shear test were used to evaluate the reliability of the proposed equation in predicting the excess pore pressure ratio in partial saturation condition
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