Failure mechanism of clay in pore water pressure loading test

Abstract

Pore water pressure loading test of clay was carried out to investigate a shear resistance of clay in land-slide slope. From the observation on shear deformation of the clay, two threshold magnitudes for pore water pressure were found out where the deformation of testing specimen rapidly increased. Through a series of pore water pressure loading tests of clay, the yield points were found to locate on the critical state line de-scribed by the shear resistance angle φ'. It suggests the design based on the yield point corresponds to that of residual strength. The transmittance time of pore water pressure from the bottom to the top of soil specimen was measured to get longer after the pore water pressure was over the yield point. The deformation of soil specimen took place very slowly as the pore water pressure closing to the failure point. The reason for the slow failure was concluded that the soil deformed with the water migration and the progressive failure of soil specimen proceeded with strain softening of soil. It suggests the reason for the slow failure of landslide. The pore water pressure loading test was simulated with the constitutive equation by Hashiguchi. The yield and failure points were shown to be well estimated.