Strain Accumulation in Soft Marine Clay due to One-Way Cyclic Load with Variable Confining Pressure

The effect of variable confining pressure on the strain accumulation in soft marine clay was investigated to gain a better understanding of the deformation characteristic in the subgrade of pavements due to traffic loading. A series of variable confining pressure (VCP) experiments and corresponding constant confining pressure (CCP) experiments were conducted on Wenzhou soft clay using an advanced cyclic triaxial apparatus. A wide range of deviatoric stress amplitudes (q^ampl), combined with different isotropic stress amplitudes (p^ampl), and partially drained conditions are simulated in the experiments. The test results indicate that the variable confining pressure significantly influences the permanent axial strain and might exacerbate the potential of subgrade invalidation in soft marine clay area. The normalized permanent axial strain (ε^p_a,1000/ε_a,1000^p,CCP) after 1000 cycles is logarithmic with the normalized stress path length (L/LCCP), and one-unit increment in the amplitude of cyclic confining pressure will induce an increment of 0.0213% in the permanent axial strain regardless of the CSR values. Based on the data from the CCP tests, a cyclic deviatoric stress ratio threshold is determined to be about 0.7, which may suggest that the upper bound of criterion will limit the cyclic traffic loadings on soft marine clayey deposit. Finally, the effect of variable confining pressure on the permanent axial strain is quantified and incorporated in a logarithmic model for the subsoil deformation prediction under traffic loading.

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