Test and numerical analysis of model rock-socketed pile

Abstract

Rock-socketed piles can hardly be loaded to failure in field tests due to their high ultimate bearing capacity. In order to investigate the pile resistance behavior along the concrete-rock interface, two rock-socketed pile models were tested in laboratory. One model was loaded to failure at the maximum applied load. It was observed that the slippage occurred along the concrete-rock interface, while the pile body and the rock mass remained intact. The mobilized pile resistance along the concrete-rock interface within the rock-socketed section was evaluated from the recorded axial strains. The results indicated that the shaft resistance was not evenly mobilized within the socket. It is clear that the mobilized pile resistance in the upper zone is much greater than that in the lower zone. In addition, a serious of numerical simulations of tests were performed by using a finite element program. The interfacial elements were adopted in the program to model the concrete-rock interface behavior. The numerical analyses indicated that notable normal stress could be produced along the concrete-rock interface due to the lateral deformation in the rock mass. The mobilization of the pile resistance along the interface was greatly influenced by the normal stress. Therefore, the mobilized pile resistance in the upper zone is much greater than that in the lower zone. The investigation suggests that the pile resistance behavior along the concrete-rock interface can dominate the working performance of the rock-socketed piles constructed in hard rocks. Furthermore, the pile resistance along the concrete-rock interface can be greatly influenced by the deformation characteristics of rock mass.

由于嵌岩桩的极限承载力很高，在现场试验中很难将其加载至破坏和监测破坏时嵌岩段摩阻力的分布特征。采用室内模型试验方法对桩1混凝土及桩1岩石界面的摩阻特性进行研究。试验中对两个嵌岩桩模型进行荷载试验，将其中一个加载至破坏。试验结果表明，破坏发生在桩/混凝土界面，而桩身及岩体内部均保持完好。另外，桩/岩石界面上的摩阻力分布是非均匀的；模型桩破坏时在嵌岩段上部产生的摩阻力远大于下部的值。数值模拟结果表明，摩阻力的这种分布特性是因为桩周岩体变形所在界面所产生的法向压应力的影响。试验结果说明，对于建造在高强度岩体中的嵌岩桩，其承载力特性极大地取决于桩/岩石界面的摩阻特性，而摩阻力的分布又受到桩周岩体变形的影响。