描述软土不排水循环应力应变响应的拟动力关系

A Pseudo dynamic Relationship for Describing the Cyclic Stress strainResponse of Soft Clays in Undrained Conditions

摘要:

依据等效黏弹性理论与蠕变理论，建立了描述一般应力状态饱和软土不排水循环应力应变响应的拟动力本构关系。该关系包括三个基本参数：循环剪切模量，阻尼比与增量循环累积应变。利用循环剪切模量与阻尼比随土单元八面体剪应变的变化描述循环荷载作用下软土的不排水循环应变，依据Mises蠕变势函数与正交流动法则确定循环累积应变增量。通过饱和软土不固结不排水循环三轴压缩试验确定这些变化关系。按确定出的参数预测循环三轴拉伸与循环扭剪试验结果。预测出的循环拉伸试验剪切模量和阻尼比随八面体剪应变的变化与试验结果吻合。对于循环扭剪试验，当循环偏应力与静偏应力方向一致时，预测出的循环累积应变随循环次数的变化与试验结果基本一致；当循环偏应力与静偏应力作用方向不一致时，预测出的循环累积应变与试验结果相比偏小。

Abstract:

In this study，we develop a pseudo-dynamic relationship describing undrained cyclic stress-strain responses of soft clay elements under general stress conditions，based on equivalent visco-elastic and creep theories.This relationship includes three basic parameters：the cyclic shear modulus，the damp ratio and the cyclic accumulative strain increment.The variation of the cyclic shear modulus and the damp ratio with the octahedral shear strain are used to describe undrained cyclic strain.The cyclic accumulative strain increment is determined based on the Mises creep potential and the associated flow rule.We determine these by unconsolidated and undrained cyclic triaxial compression tests of soft soils.We made cyclic triaxial extension and torsion test predictions using the parameters determined.Predicted variations of the cyclic shear modulus and the damping ratio with the octahedral shear strain are basically in agreement with the test results from the cyclic triaxial extension tests.Predicted variations of the cyclic accumulative strain with respect to the number of cycles is also basically in agreement with the test results for the cyclic torsion tests wherein the static and cyclic deviatoric stresses have the same direction.The predicted variations of the cyclic accumulative strain are less than those of the test results when the direction of the static deviatoric stress is different from the direction of the cyclic deviatoric stress in the cyclic torsion tests.