Earthquake induced deformation and failure of soft sediments

点击翻译按钮获取中文摘要

The deformation and failure of soft sediments induced by earthquakes were experimentally investigated with special reference to (A) high strain-rate and (B) repeated inversion of shearing. The following results are demonstrated ;(A) As increasing strain rate from 10^<-3> to 10^0/s, (1) shear strain is not localized, and homogeneously deformed, (2) change from limited progressive failure to simultaneous failure, (3) angle of shear plane (α) decrease from 70°to 50°, and (4) shear strength becomes larger. In these results, relationship between (3) and (4) contradict with each other in the sense of mechanics. In general, higher shear strength means higher internal friction as well as larger angle of shear plane (α). However, these results from plane-strain shear tests seems contrary to usual cases. As one reason, it was suggested that the effective stress between particles is reduces due to high pore pressure. (5) Regardless of strain rate, the amount of pore pressure is almost equal. Therefore, the expected high pore pressure under high strain rate was not realized. (6) Under strain rate less than 10^<-3> s^<-1>, angle of shear plane does not change.(B) Minor fracture array was formed under low strain by repeated inversion of shearing, which is geometrically equivalent to the vein structures found in argillaceous sediments of active plate margin. (1) They are initiated as a conjugate Riedel shear under simple shear before failure with major Riedel shear ; (2) They grow with repetition of stress inversion ; (3) Higher void-ratio and low strain are preferable conditions. (4) The aspect ratio of the shear plane, height to spacing, is controlled by the width of the shear zone.