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

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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