Effects of the Volumetric Strain Due To Pre-Shaking on the Liquefaction Resistance

Abstract eng:
The resistance of sandy soil to liquefaction is influenced not only by relative density and particle gradation (e.g. fine content) but also by many factors including aging effects. Previous researches pointed out that sandy soils resting for several thousand years should have a greater resistance to liquefaction because of improved interlocking and cementation of neighboring sand grains associated with their extended time under a static pressure and being subjected to many earthquake shakings (i.e. pre-shearing). The interest of this study is pre-shearing effects on the liquefaction resistance. Some researchers have pointed out that pre-shearing effects on liquefaction resistance depends on the cyclic shear strain, numbers of cycles and the cyclic shear stress of the pre-shaking, but none of these factors can be used to assess the pre-shearing effect on liquefaction resistance. Besides those factors, it is considered that volume of contraction during and after preshearing might be an influential factor to rise the liquefaction resistance. This assumption is made because volumetric strain plays dominant role of controlling the liquefaction resistance when volumetric contraction can occur during cyclic shearing. Undrained cyclic shear of unsaturated sand, membrane penetration and system compliance effects and partial drainage during shaking may be the cases. In order to assess the effect of the volumetric strain due to pre-shearing on the liquefaction resistance series of cyclic triaxial testing with pre-shearing histories were conducted. The volumetric strain due to preshearing was measured and the liquefaction resistance ratio, that is the ratio of the liquefaction resistance of a sand with preshaking history to that without pre-shaking, was obtained. Test results show that liquefaction resistance ratio increases with increasing in the volumetric strain in a unique way regardless of the relative density, number of cycles and stress level of the pre-shaking. The relationship between liquefaction resistance ratio and the volumetric strain for the tests are compared with those for undrained cyclic tests on unsaturated sand and on saturated sand with membrane penetration effect. It is found that all those results agree quite well, which strongly suggest that the volumetric strain is the only parameter which plays the dominant role of controlling the enhancement of liquefaction resistance due to pre-shearing.

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