Investigation of Soil-water Coupled Behavior of Saturated Clay near/at Critical State and Its Application to Deformation and Failure Problems

为了研究正常固结/超固结粘土的“时变特性”，进行了三轴压缩试验和采用分载面凸轮粘土模型的土-水耦合分析。分叉分析可以用孔隙水迁移效应代替粘塑性来解释粘土的“时变特性”。本研究进行的三轴压缩试验结果表明：1)土样的破坏模式由土样的孔隙水迁移模式转变为土样的两种破坏模式，从而产生不排水蠕变破坏；2)在排水条件下，超固结粘土在恒定荷载作用下，由于试验过程中的吸水作用，表现为渐进破坏。超固结粘土试件的破坏历时约6小时。轴向应变率对轴向应变的影响表现为渐进破坏。不排水b-…平面应变饱和土柱的缺陷敏感分叉采用土-水耦合有限变形分析方法对更多的基础进行了研究。对土样采用初始二阶余弦曲线几何缺陷。在加载边界上施加线性约束条件，即不改变角度和不改变方向。假定土体服从次荷面CaM-Clay模型。当施加在试件上的载荷保持在分叉点附近时，载荷位移曲线开始偏离主路径，最终接近不稳定的一阶振型路径。这种模式转换是由于荷载-位移曲线峰值后的孔隙水迁移，从而产生低的不排水剪切强度，描述了传统上归因于粘塑性的不排水蠕变。与试验相似，当外加荷载保持不变时，重度超固结土样中轴向应变率相对于轴向应变的增加，说明了高剪切区由于软化而导致的渐进性破坏。较少

In order to investigate "time dependent behavior" of normally consolidated/overconsolidated clay, triaxial compression tests and the soil-water coupled analysis employing the sub-loading surface Cam clay model have been carried out. The bifurcation analysis can explain "time dependent behavior" of clays by using pore water migration effect instead of visco-plasticity. The triaxial compression tests carried out in this research showed that : 1) Undrained creep failure occurs due to the change of 1^<st> failure mode to 2^<nd> mode of soil specimen that associated with pore water migration. 2) Overconsolidated clay exhibits progressive failure under constant loading in drained condition due to the absorbed water during testing. It took about 6 hours for the failure of overconsolidated clay specimen. The progressive failure is observed with the fluctuations of axial strain rates against axial strain.Imperfection-sensitive bifurcation of a plane strain saturated soil column with undrained b … More oundaries is investigated by soil-water coupled finite deformation analysis. An initial cosine-curve geometrical imperfection of 2nd mode is applied to the soil specimen. The linear constraint conditions, "no angle change and no direction change" are imposed over the loaded boundary. The soil is assumed to follow the sub-loading surface Cam-clay model. When the load application to the specimen is held at a point near the bifurcation point, load displacement curve starts to deviate from the main path, ultimately approaching unstable 1st mode path. This mode switching due to pore-water migration after the peak in load-displacement curve, that yield low undrained shear strength describes the undrained creep, which is traditionally attributed to visco-plasticity. Similar to the experiment, the increase in axial strain rate against axial strain in heavily overconsolidated soil specimen when the applied load is kept constant, illustrates the initiation of progressive failure due to softening in the highly sheared zones. Less