移动状态边界面法在黏性土不排水蠕变孔压分析中的应用

Use of time-dependent SBS method in undrained creep pore-pressure analysis of clay

在黏性土的各种流变现象的数学模拟研究中,不排水蠕变孔压方程几乎是空白。基于临界状态土力学理论,采用与时间相关的移动状态边界面法,给出了适用于正常固结黏性土的不依赖状态边界面具体形态的不排水蠕变孔压公式。正常固结黏性土的不排水蠕变孔压可以看作是体积蠕变势和剪应力水平增大造成的剪缩这两种作用的结果,前者与参数c_a/c_c有关(c_a为次压缩指数,c_c为压缩指数),后者则与状态边界面的具体形态有关。在此基础上进一步给出了可方便用于试验数据分析的双对数和单对数形式的两个公式。以修正剑桥模型椭圆形状态边界面为例,分析了双对数和单对数坐标系下蠕变孔压曲线的斜率m和m′与土的流变参数c_a/c_c的关系。采用提出的方法,很好地预测了Walkers给出的Ledaclay黏土的蠕变孔压系数,并基于以上两种作用解释了Leda clay黏土的蠕变孔压形成的机制。

Undrained creep pore-pressure equation is almost a blank in the field of mathematical modelling of rheology behaviors of clay. Based on the theoretical framework of critical state soil mechanics, the movement of the state boundary surface（SBS） with time was formulated. Then the undrained creep pore-pressure equations for normally consolidated clay were presented, which is independent on the shape of the SBS and constitutive models. The undrained creep pore-pressure of normally consolidated clay is interpreted by the coupled effect of volumetric creep and shear compaction, the former is relating to the parameter c_a/c_c and the latter is relating to the shape of SBS. Two kinds of equations with double log and single log forms which can be easily used in pore-pressure test data analysis were then presented. Using the SBS of modified Cambridge model as an example, the slopes of the pore-pressure curves in double and single log scales, defined by m and m′ respectively, were compared with the parameter c_a/c_c. The proposed method statistically simulated the pore-pressure coefficients of Leda clay obtained by Walker, and interpreted the pore-pressure coefficients by the two mechanisms.