Pore Water Pressure and Settlement Induced By Multi-Directional Cyclic Shear of High Plasticity Clay

Abstract eng:
In this paper, by using the multi-directional cyclic simple shear test apparatus, normally consolidated specimens of Kitakyushu clay (plasticity index, I p = 63.8) were subjected to the uni-directional and multi-directional cyclic shears (in the multi-directional cyclic shear test, uniform cyclic shear strains were applied to the soil specimen from two perpendicular directions with various phase differences) in which the shear strain amplitude was changed in the range from 0.05% to 2.0%. The cyclic shear induced-pore water pressure (U dyn ) and settlement in strain (ε v , %) were observed and compared with the calculated ones obtained by the conventional estimation method, where the pore water pressure ratio (U dyn /σ’ v0 ) is expressed by equations including the number of cycles (n) and two experimental parameters (α and β). It is shown from the observed and calculated results that the changes of α and β can be expressed by a function of shear strain amplitude. In the recompression stage after undrained cyclic shear, the compression index for the uni-directional cyclic shear C dynU is obtained as 0.233×C c and for the multi-directional cyclic shear C dynM as 0.250×C c , respectively, where C c is the virgin compression index. In conclusion, the cyclic shear induced-settlement of clay with high plasticity index can be predicted by using these indices.

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