Liquefaction Properties of Toyoura Sand in Cyclic Tortional Shear Tests Under Low Confining Stress

Abstract

A series of undrained cyclic torsional shear tests was conducted to investigate liquefaction properties of Toyoura sand under low confining stress. Hollow-cylindrical specimens were prepared by air pluviation at a relative density of about 55%. After being saturated, they were anisotropically consolidated to an effective vertical stress of 9.8, 29.4 and 98.1 kPa, while keeping the effective horizontal stress to be half of the vertical one. They were subjected to undrained cyclic torsional shear without allowing any vertical displacement of the top cap. The amplitude of the cyclic shear stress was kept constant with correction for the effects of membrane force on the measured values. The liquefaction resistance was found to increase with the decrease in the confining stress, while correction for the effects of membrane penetration did not significantly affect this tendency. Analyses of the test results revealed that the liquefaction properties were affected by the mobilization of shear resistance under extremely low effective stress states and the stress level-dependency of shear modulus that was normalized by the confining stress. Finally, by introducing a concept of apparent increase in the effective mean principal stress, a simplified procedure to estimate the liquefaction resistance under low confining stresses was proposed.

Behavior of Liquefied Sands Under Extremely Large Strain Levels in Cyclic Torsional Shear Tests

“…This loading device is a displacement-controlled type from a mechanical point of view, whereas cyclic shear tests by keeping the speciˆed shear stress amplitude could be conducted by using a computer which monitors the outputs from the load cell and controls the device accordingly (refer to Koseki et al (2005) for the details of the stress computations) . The procedure that was employed in the present study to correct for the membrane force will be explained later.…”

“…In order to investigate into such strain softening properties, the observed liquefaction behaviour was examined in terms of the relationship between the ratio of modiˆed shear stress to modiˆed current eŠective mean principal stress, (t-Dt)/( p?＋Dp? ), which was employed by Koseki et al (2005). Figure 15 shows the deˆnition of Dt and Dp?…”

“…Regarding such behaviour, Towhata and Gallage (2003) reported that the sand behaviour under extremely low eŠective stress states is aŠected by the strain rate, exhibiting viscous properties. Furthermore, Koseki et al (2005) reported that this behaviour is possibly aŠected by both the eŠects of interlocking among sand particles that could be mobilized even under zero eŠective stress state and the eŠect of viscous interaction between pore water and the surface of sand particles. In the present study, the attempts made by Koseki et al (2005) were adopted, which include introduction of apparent increase in the eŠective mean principal stress, Dp?, and the shift in the shear stress, Dt, to correct for the eŠects of the mobilization of shear resistance under extremely low eŠective stress states and possible measurement error, respectively.…”

Study on Dip Slope Failure at Higashi Takezawa Induced by 2004 Niigata-Ken Chuetsu Earthquake

“…12), and thus, no lateral constraint was applied to the specimen during the consolidation process. As the membrane is thin and highly deformable (Young's modulus＝1492 kPa, after Koseki et al, 2005), a shear band can form without additional artiˆcial interference. On the other hand, since the compensative shear stress is not well mobilized at the interface between the specimen and the membrane, the local stress distribution within the specimen becomes non-uniform.…”

Liquefaction Resistances of Unsaturated Non-Plastic Silt

“…This resulted in the diŠerence in eŠective stress, sc-uw0, ranging between 36 kPa and 106 kPa. According to Koseki et al (2005) liquefaction resistance may change a few percentage due to the diŠerent eŠective conˆning pressures in this stress range. This change is regarded to be small and the eŠect of conˆning pressure on the liquefaction resistance is not considered in this study.…”