下伏空洞岩石地基极限承载力计算方法研究

针对岩溶区下伏空洞嵌岩桩桩端岩石地基极限承载力问题,进行了下伏空洞桩端岩石地基的破坏模式分析。基于Hoek-Brown强度准则剪应力形式,理论推导出不同顶板厚度下下伏空洞岩石地基及完整岩石地基极限承载力计算方法。当顶板厚度为1~3倍桩径时,采用极限分析上限原理推导了冲切破坏模式下泛函形式的下伏空洞岩石地基极限承载力表达式。运用变分原理得到冲切破坏线方程,进一步利用偏导求得了下伏空洞岩石地基极限承载力计算公式。当顶板厚度大于5倍桩径时,采用特征线法推导出塑性破坏模式下完整岩石地基极限承载力计算公式。当顶板厚度为4倍桩径时,利用完整岩石地基极限承载力与承载比理论,采用S型生长曲线拟合出冲切剪压复合破坏模式下的极限承载力值。通过与1~5倍厚径比条件下的下伏空洞岩石地基极限承载力室内模型试验结果对比,计算值与实验所得数据吻合良好。

Study on Ultimate Bearing Capacity Calculation Method of Rock Foundation over Cavern

Aiming at the ultimate bearing capacity of rock foundation at pile tip of caved rock-socketed pile in karst area,the failure mode of rock foundation at pile tip of caved pile was analyzed in this paper.Based on the shear stress form of Hoek-Brown strength criterion,the calculation method of ultimate bearing capacity of hollowed rock foundation and intact rock foundation under different roof thickness was deduced theoretically.When the thickness of the roof was 1-3 times the pile diameter,the ultimate bearing capacity of the underlying hollow rock foundation under punching failure mode was deduced by using the upper-bound limit analysis method.The equation of punching failure line was obtained by means of variational principle,and the explicit calculation formula of ultimate bearing capacity of underlying hollow rock foundation was obtained by partial derivation.When the thickness of roof was more than 5 times the diameter of pile,the formula of ultimate bearing capacity of intact rock foundation under plastic failure mode was deduced by using characteristic line method.When the thickness of roof was 4 times the diameter of pile,the ultimate bearing capacity of intact rock foundation and bearing ratio theory were used to fit the ultimate bearing capacity value of punching shear compression failure mode by S-shaped growth curve.Compared with the laboratory model test results of ultimate bearing capacity of underlying hollow rock foundation under the condition of 1-5 times thickness-diameter ratio,the calculated values were in good agreement with the experimental data.