土岩组合岩体中抗拔桩极限承载力的确定

Determination of ultimate bearing capacity of uplift piles in combined soil and rock masses

为全面探究土岩组合岩体中抗拔桩的极限承载力,结合工程岩土参数及试验数据,运用Flac3D数值分析软件对其进行数值模拟分析,即可得到土岩组合岩体中抗拔桩的极限承载力。基于被动状态下的Kotter极限平衡方程式求解土层提供的抗拔力,根据岩石强度,基于Hoek-Brown破坏准则求解抗拔桩嵌岩端岩体的抗拉强度,从而可计算得到嵌岩端岩体的抗拔力;由静力平衡原理,叠加土层及嵌岩端岩体提供的抗拔力及破坏锥体重量,即可得到土岩组合岩体中嵌岩抗拔桩的极限承载力理论解析式。在嵌岩深度较小的情况下,该解析式的理论计算值与数值模拟分析值相接近,但随着嵌岩深度的增加,理论计算值会偏离数值计算值。故结合数值模拟试验值,对提出的极限承载力理论解析式作进一步的修正,得到修正后的极限承载力解析式能反映嵌岩端岩石风化程度、嵌岩深度、土层厚度、桩长对极限承载力的影响。运用修正后的解析式对该地质条件下不同抗拔桩的极限承载力计算表明:数值模拟结果与理论计算结果相吻合,说明所建立的抗拔桩极限承载力解析式的方法是可行的。同时,运用该方法可确定类似工程中嵌岩抗拔桩的极限承载力。

In order to comprehensively explore the ultimate bearing capacity of uplift piles in combined soil and rock masses, combined with engineering geotechnical parameters and experimental data, the Flac3D numerical analysis software is adopted to carry out numerical simulation analysis to obtain the ultimate bearing capacity of uplift piles in the composite rock mass. The Kotter limit equilibrium passive equation is employed to solve the pull-out force provided by the soil layer. And based on the rock strength, the strength of the rock mass embedded in the rock pile can be determined by the Hoek-Brown failure criterion. In turn, the pull-out force of the rock mass embedded in the rock can also be obtained. In addtion, based on the principle of force balance, the ultimate bearing capacity of rock in lay uplift piles in the combined rock mass can be obtained by superimposing the pull-out resistance provided by failure rock layer and the rock mass on the gravity of failure cone. The theoretical calculation value obtained from the analytical formula is close to the numerical simulation analysis value in the case of small rock-socketed depth. However, with the increase of the rock-socketed depth, the theoretical calculation value fluctuates within a certain range around the experimental value. Therefore, combining with the numerical results, the theoretical formula of the ultimate bearing capacity is modified. Finally, by taking the consideration of the effect of rock wathering, rock-sockering depth, soil thickness and pile length, the improved ultimate bearing capacity analytical formula is obtained. The modified analytical formula is used to predict the ultimate bearing capacity of different uplift piles under different geological conditions. The predicted results show that the numerical simulation results are consistent with the theoretical calculation results, which means the analytical method of the ultimate bearing capacity of uplift piles in this paper is feasible. Based on a part of test result, the ultimate bearing capacity of different rock-socked piles with different rock-socked depths in similar projects can be determined by this method.