Cyclic-Induced Soil Disturbance in Structured Soft Clay: Experimental Evidence from Undisturbed and Reconstituted Specimens

Seismic damage has been observed not only in liquefiable sandy soil layers but also in thick deposits of soft clayey soils, which are characterized by the destruction of the soil structure, leading to strain softening. Previous studies conducted numerical simulations and defined this phenomenon as soil disturbance, which refers to the simultaneous reduction in stiffness and peak shear strength. To fill the research gap, this study systematically compares the post-cyclic degradation behavior of stiffness and peak shear strength of UDS and REC specimens derived from the same material. Based on the experimental results, the peak shear strength and rigidity of the UDS specimens simultaneously decrease, as the number of cycles increases. In contrast, the peak shear strength degradation effect is absent in the REC samples; both specimens exhibited loss in stiffness. The reduction in stiffness of UDS specimens was slower than that of REC specimens due to aging effects. Nevertheless, both effects on UDS and REC specimens are due to soil disturbance, which is defined in the numerical simulations of previous studies. Hence, the effects of soil disturbance can be summarized as (1) a reduction in the initial stiffness of soft clay and (2) a reduction in the mean effective stress during cyclic loading.