循环荷载下饱和砂土的孔压触变性

Thixotropy induced by vibration pore water pressure of saturated sands under cyclic loadings

将液化土体视为流体进行液化效应分析是一个前沿的技术思路。其中,合理描述液化土体的流体性质是一个关键问题。提出循环荷载下饱和砂土孔压触变性的概念和基本设想。采用点差法计算相变后饱和砂土流动性曲线各点曲率,给出了依据流动性曲线加速增长段的最大曲率确定初始流体状态的经验方法。基于饱和砂土不排水循环三轴试验,发现进入流体状态后的饱和砂土应力–应变率关系满足Cross型触变性流体状态方程,其内部结构参数与土中残余有效应力比具有正比例关系;此时Cross型触变性流体速率方程描述的物理实质即为土体内的孔压增长过程。试验结果印证了论文提出的基本设想,证明了循环荷载下进入流体状态后的饱和砂土具有孔压触变性流体特征。

It is a frontier technology used in the analysis of soil liquefaction effects that the liquefied soils are regarded as the fluid. In which, a key problem is how to describe the fluid characteristics of the liquefied soils. As a basic assumption, the concepts of the thixotropic fluid induced by the vibration pore water pressure are introduced to analyze fluid characteristics of the saturated sands after entering the initial fluid state. The initial fluid state is determined according to the maximum curvature of the accelerating growth phase of the flowing property curve. The flowing property curve can be obtained by employing the undrained cyclic triaxial experiments of the saturated sands, and the curvature is calculated using the point difference method. By analyzing the data from the conducted undrained cyclic triaxial experiments, it is discovered that the relationships between shear stress and shear strain rate of the saturated sands after the initial fluid state meet the state equation of the Cross thixotropic fluid. The structural parameter of the fluid is proved to be directly proportional to the residual effective stress ratio. Additionally, it is also discovered that the physical essence described by the rate equation is the growth process of the vibration pore water pressure resulting in the inner structural damage of sands. It is concluded that the proposed basic assumption is confirmed. It is also proved that the saturated sands after entering the initial fluid state possess the characteristics of the thixotropy fluid induced by the vibration pore water pressure.