Elastoplastic analysis of cylindrical cavity expansion in natural sedimentary soft clay with structure damage

Field construction on natural sedimentary soft clay may induce additive soil disturbance, which results in the structural damage and strength reduction of soils. According to the relationships among plastic shear strain, measured permeability coefficient, undrained strength and radical distance, a logarithmic disturbance function is proposed to describe the variation of yield strength of soils in the plastic damaged zone. The yield stress ratio (YSR) and sensitivity (S_t) are used as structural parameters to represent the initial structural stability and strength variability, respectively. By using the disturbance function and the structured Cam-clay yield criterion, the closed-form solutions are derived for the stress distributions in the elastic and plastic zones during cylindrical cavity expansion in natural soils. If setting the sensitivity as unity, the solutions are reduced to the conventional elastoplastic solutions of the cylindrical cavity expansion in soils without considering the structural damage. The derived elastoplastic solutions are verified by comparing the theoretical calculations with the experimental data of the excess pore pressures caused by the installations of vertical drains and piles. Furthermore, the effects of the structural damage on the magnitude and distribution of stress around the cavity are studied. The results show that a better structural stability that is signaled by a higher value of YSR leads to a smaller radius of the plastic zone and a greater radial stress. A higher value of S_t leads to a smaller radial stress and a greater radial excess pore pressure. The proposed theoretical solutions significantly contribute to the accurate prediction of the compaction effect of pile driving and the reasonable revelation of the measuring mechanism of the in-situ tests.