修正Mohr-Coulomb准则下倾斜基岩中桩端极限承载力研究

Study on ultimate bearing capacity of pile tip in inclined rocks based on modified Mohr-Coulomb criterion

为计算倾斜岩面浅嵌岩桩极限承载力,本文基于修正Mohr-Coulomb强度准则提出了倾斜岩面浅嵌岩桩桩端承载力计算方法。采用特征线法构建了桩端面以下塑性发展区,考虑岩面倾斜角几何关系,推导了倾斜岩面位移滑移场;进一步通过黎曼不变量控制方程,求解了倾斜岩面浅嵌岩桩基极限承载力公式。分析了倾斜岩面坡角、岩体完整性参数以及岩体内摩擦角等因素对桩端承载力的影响。结果表明:浅嵌岩桩基嵌入深度达到极限嵌入比时,桩基达到极限承载力;当嵌入比大于极限嵌入比时,桩端承载力系数不受倾斜坡角和嵌入比影响,此时可按平地桩基进行分析计算;极限嵌入比随倾斜坡角的增大呈幂函数增大,且在岩石完整性较差时,极限嵌入比随岩体内摩擦角的增大而显著增大;当嵌入比小于极限嵌入比时,桩端承载力系数随倾斜坡角的增大近似线性减小,需考虑岩面倾角对桩基承载力的影响。

In order to calculate the ultimate bearing capacity of shallow rock-socketed pile in inclined rocks,an analytical method for calculating the tip bearing capacity of a shallow rock-socketed pile in inclined rocks was proposed based on the modified Mohr-Coulomb strength criterion.The plastic zone below the pile tip was constructed by the characteristic line method.The displacement field of inclined rocks was derived considering the geometric relation.Combined with the Riemann's invariant governing equation,the ultimate bearing capacity formula of shallow rock-socketed pile foundation in inclined rocks was further solved.The influences of the inclined slope angle,the Geological Strength Index(GSI) and the friction angle on the bearing capacity of pile tip were analyzed.The results show that the ultimate bearing capacity of shallow rock-socketed pile is reached when the embedment depth reaches a limit embedment ratio.When the embedment ratio is greater than the limit embedment ratio,the load factor of pile tip is not affected by slope angle and embedment ratio,which can be calculated and analyzed according to a pile in flat rocks.The limit embedment ratio increases as a power function with the increase of the slope angle.When the rock integrity is poor,the limit embedment ratio increases significantly with the increase of the friction angle.When the limit embedment ratio is not reached,the load factor for the ultimate bearing capacity of the pile decreases approximately linearly with the increase of the slope angle,so the influence of the slope angle of the rock on the bearing capacity of the pile foundation should be considered.