Research On Squeezing Effects Of Jacked Pile In Layered Soil Based On The Model Test And Finite Element Simulation

The subject for squeezing effect of jaked piles in Binhai New Area was proposed, especially exacerbation of compaction in the junction of the hard and soft soils. Its mechanism and laws were studied for solving the problem of theory laged behind the engineering practice. The paper firstly reviewed and analyzed the research methods of squeezing effect, and pointed out their advantages and disadvantages in detail. Then based on the above analysis, some main original works were made as follows:1. Based on the laboratory test the sliding friction and its time effect between jacked pile and soil in Tianjin Binhai New Area were studied with the modified direct shear apparatus. Angle of external friction and its law between jacked pile and soil were obtained. The mechanism of time effect was also summarized. The reaults showed that friction resistance was related with soil type, and was approximately linear to the vertical pressure. The increase of friction resistance between pile and clay or mud silt was proportional to the increase of carrying capacity of the pile with the time going by.2. Based on model test, squeezing displacement field, squeezing stress field and excess pore water pressure in layered ground were analyzed in detail. Following conclusions were pointed out: (l) the horizontal displacement near the boundary between the harder soil layer and the softer soil layer would increase abruptly. (2) There was an obvious "sheltering effect" of the pile group. (3) There was an obvious horizontal stress increase when the pile pressed into the rigid soil. (4) The excessive pore water pressure dissipated with the time increased. (5) After the soil was squeezed, the level of external friction angle increased with the increase of soil depth, but decreased with the increase of radial distance. (6) After the pile penetration, the density of soil around the pile increased. The water content of upper soil increased, but the water content of lower soil decreased, and both decreased as the radial distance increased. 3. A two-dimensional axisymmetric finite element model which accorded with actual process of jacked pile pressed into homogeneous soil and layered soil was established with ABAQUS. The continuous process of pile penetrated into homogeneous soil and layered soil was simulated, and compared with the model test. The result showed that the laws obtained from the above two methods were basically consistent, but the curves of numerical simulation were more smoother.