Bearing Mechanism Of Socketed Pile In Soft Rock

Rock-sockted piles are typically selected when the large loads of superstructrues, such as high-rise building and bridge footings, need to be transferred to competent bearing strata so as to restrict deformations within the serviceability limits. With the widespread of soft rocks in China, the socketed piles in soft rock are often used in practice. The pile in soft rock are neither like that in soil nor in hard rock. In relation of piles in soil, the dilation between the pile and the soft rock occurs when the pile is loaded and the interface has the constancy normal stiffness. Additionally, the failure zone of soft rock around the model pile tip was a similarly shaped deformation bulb. In relation of piles in hard rock, the failure may occur located in the interface or in the soft rock. The displacements at ultimate side resistance and base resistance are larger and the overburden pressure shows the relative evident effect on the bearing capacity.In this study, the methods of individual element test, physical modelling, and theory analysis were carried out to investigate the bearing mechanism of rock-socketed pile in soft rock under axial loading. The research of piles in soft rock includes the mechanic prosperities of soft rock, bearing behavior of pile base and pile shaft, load transfer mechanism and settlement analysis. The main conclusions are as follows:(1) By means of a seize of unconfined tests on specimens with different mass ratio of these institutes including sand, plaster, cement, concrete-hardening accelerator and water, the soft rock specimens with defined strength and deformation modules, which is without the compression stage, is obtained easily and efficiently. It is convenient and effective to use these materials to simulate soft rock with weathering formation underling a certain stress level, especially for the purpose of model tests.(2) The self-designed apparatus allows for the control of vertical pressure, which can simulate the influence of the pressure of soil on the bearing behavior. The ultimate shaft resistance was fully mobilized and followed by the ultimate base resistance and the softening effects of shaft resistance is necessary to been taken into consideration in the design process. The overburden pressure and the socketed depth have mina influence on the ultimate side resistance and residual side resistance. For the base resistance, it increases with the increasing overburden pressure and socketed depth, but the effect of depth should pay much attention.(3) With the aid of CT scanning, the failure zone of soft rock around the model pile tip is captured and it is a similarly shaped deformation bulb. The spherical cavity expansion theory is proposed to calculate the base resistance of piles in soft rock with the correction coefficient.(4) The constant normal stiffness shear tests are used to investigate the shear strength of the interface between the simulated soft rock specimen and the pile with varying roughness factor. And the specimens with inclined surface between the pile and the natural soft rock are conducted in triaxial compressive tests. The ultimate and residual side resistance of the socketed in soft rock can be obtained by comparing the results of the two methods.(5) The relationship between average side resistance and settlement are normalized by the comparison of results of model tests and in-suit tests, as well as the relationship between base resistance and settlement. Based on these normalized relation, the settlement can be predicted by the improved load transfer method.