考虑软黏土结构性损伤的圆柱孔扩张弹塑性分析

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

针对天然沉积软黏土中施工扰动导致原位土结构性损伤和强度降低的特征,根据圆孔扩张过程中产生的塑性剪切应变以及实测的渗透系数与不排水强度随径向距离的变化规律,提出对数式的原位扰动度函数以描述塑性损伤区的屈服强度变化;基于结构性剑桥模型屈服准则,采用屈服应力比和灵敏度分别表征初始结构稳定性和结构强度可变性大小,并与扰动函数相结合,推导了考虑土结构性损伤的软黏土柱孔扩张弹塑性解,表达式中灵敏度值为1时退化为不考虑结构损伤的传统解。进而通过竖井和沉桩施工引起的超静孔隙水实测结果与理论计算值的对比,验证了本文理论解的有效性;并分析了土结构及其损伤对柱孔扩张效应的影响,结果表明:屈服应力比越大,塑性区半径越小,径向应力越大,超静孔压随径向距离先增大后减小;灵敏度越大,径向应力越小,超静孔压越大。分析推导结果对准确预测挤土效应与合理揭示孔压静力触探等原位试验测试机理具有实用价值。

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 （St） 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 St 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.