Earthquake induced deformation and failure of soft sediments

本文对地震作用下软沉积物的变形和破坏进行了实验研究，特别涉及（A）高应变率和（B）剪切反复反转。结果表明：（1）随着应变速率从10^0<-3>/s增加到10^0/s，（2）剪切应变不再局部化，而是均匀变形，（3）剪切面角（α）从70°减小到50°，（4）剪切强度增大。在这些结果中，（3）和（4）之间的关系在力学意义上是相互矛盾的。一般而言，较高的剪切强度意味着较高的内摩擦力以及较大的剪切面角（α）。然而，这些结果从平面应变剪切试验似乎相反，通常的情况下。作为一个原因，有人认为，颗粒之间的有效应力是由于高孔隙压力降低。(5)无论应变速率如何，孔隙压力的大小几乎相等。因此，在高应变速率下，预期的高孔隙压力没有实现。(6)在应变速率小于10^<-3>s^<-1>时，剪切面角基本不变。(B)在低应变条件下，多次剪切反转形成了小断裂阵列，与活动板块边缘泥质沉积物中的脉状构造在几何学上是等价的。(1)它们是在简单剪切作用下以共轭Riedel剪切形式产生的，然后以Riedel剪切为主破坏;（2）它们随着应力反转的重复而增长;（3）较高的孔隙比和较低的应变是较好的条件。(4)剪切平面的纵横比（高度与间距）由剪切区的宽度控制。

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.