Abstract

A substantial amount of work on the cyclic behaviour of cohesionless soil has been performed after neglecting the reality of stratification existing nearby marine structures or alluvial plains. This complicated mechanism of stratified soil failure on earthquake-induced soil liquefaction is affected significantly by the presence of a less permeable soil layer. Several past studies investigated that under the action of dynamic loads, the presence of a silt layer in homogeneous sandy soil crucially modifies the pore pressure dissipation characteristics, axial strain rate and stress–strain behaviour of the whole stratified specimen. In the present study, cyclic behaviour of sand specimen interlayered with silt layer has been presented in respect of its pre-and post-liquefaction behaviour. Undrained stress-controlled cyclic triaxial tests have been performed on homogeneous sand specimens and on specimens interlayered with a silt layer, placed at H/4, H/2 and 3H/4 (where H is the height of the specimen from the top) to signify the role of placement depth. The instability and failure of such specimens have been compared using the failure line and phase transformation line. Few key observations suggested that the number of liquefaction failure cycles enhanced two times and secant modulus (under post liquefied state) improved by 4.8 times when the placement depth of the silt layer increased from H/4 to 3H/4 under similar loading conditions. Additionally, the role of initial static shear stress has been investigated at three different confining pressures in a few stratified specimens. It has been observed that failure of the stratified specimen is due to the obstruction of pore water movement caused by the presence of the silt layer. A comparison of the present work has been made with significant studies using liquefaction resistant curves to ensure the efficacy of this study.

摘要

在忽略了附近海洋结构或冲积平原存在分层的现实之后，人们对无粘性土的循环行为进行了大量的工作。地震引起的土壤液化的分层土体破坏的复杂机制受到渗透性较差的土层的显着影响。过去的几项研究表明，在动荷载作用下，均质砂土中淤泥层的存在极大地改变了整个分层试件的孔隙压力耗散特性、轴向应变率和应力应变行为。在本研究中，介绍了夹有粉砂层的砂样的循环行为及其液化前和液化后的行为。H /4、H /2 和 3 H /4（其中H是试样距顶部的高度）表示放置深度的作用。使用失效线和相变线比较了此类样本的不稳定性和失效。一些关键观察结果表明，当粉土层的放置深度从H /4 增加到 3 H时，液化破坏循环次数增加了两倍，割线模量（液化后状态下）提高了 4.8 倍/4 在类似的负载条件下。此外，还研究了几个分层样本在三种不同围压下初始静态剪应力的作用。据观察，分层试件的失效是由于淤泥层的存在阻碍了孔隙水运动。目前的工作与使用抗液化曲线的重要研究进行了比较，以确保本研究的有效性。