圆孔扩张理论被广泛用于静力触探(CPT)和静压沉桩等问题的贯入阻力或挤土位移分析预测中.目前结构性黏土中的圆柱孔扩张解答难以考虑扩孔过程中土体结构破坏或退化影响,一定程度上限制了该理论解答的工程适用范围.将锥尖或桩端贯入作为球形孔的扩张挤土过程,基于结构性黏土剑桥模型和塑性区大应变理论,将球孔扩张不排水问题归结为各有效应力分量的常微分方程组边值问题,以弹塑性边界上应力值为边值条件对该问题进行求解.结果表明,随着土体结构性增强,球孔周围的临界状态区和塑性区范围减小,扩孔应力增大,超固结土的应变软化特征和剪胀性更明显;对于初始应力相同的结构性黏土,各有效应力分量在孔壁附近均趋于对应重塑土中的应力分量,说明土体在扩孔扰动过程中发生了结构破坏或退化.最后将确定的扩孔应力用于CPT贯入阻力及孔隙水压力的理论计算中,与已有解答进行对比分析,发现考虑土体结构性影响后能得到与实测值更接近的预测结果.

The cavity expansion theory is widely used in the analysis and prediction of cone resistance and lateral displacements in cone penetration test (CPT) and pile installation. Nowadays, the existing theoretical solutions for cavity expansion in structured clay cannot consider the influences of structure degradation on the mechanical behaviors of soil during the expanding process, which limits its applications in practical engineering to some extent. Therefore, taking the penetration of cone or pile tip as a spherical cavity expansion process in soil, based on the structured Cam-Clay (SCC) model and the large strain theory in plastic zone, the undrained spherical cavity expansion problem could be attributed to a boundary value problem of a system of ordinary differential equations about effective stress components. The equations then could be solved with stresses on the elastic-plastic boundary serving as boundary conditions. The results show that, with strengthening of soil structure, the plastic and critical state zones narrow, the internal cavity stresses increased, and the softening behavior and dilatancy of over-consolidated soil become more significant. For structured clay with the same initial stresses, the effective stress components adjacent to cavity wall overlap with that of the corresponding reconstituted soil, which indicates that the degradation of soil structure occurs during the soil-disruption accompanied expansion process. Finally, the internal cavity stresses derived from the proposed solution were used for theoretical calculation of cone resistance and pore pressure in CPT. A comparison of the existing solution with the results calculated indicates that the results obtained with consideration of soil structure are closer to the measured values.