被动双桩侧向土压力群桩效应的三维数值研究

Three-dimensional Numerical Studies on the Group Effect of the Lateral Soil Pressure along the Pile Shafts for Coupled Passive Piles

被动桩侧向土压力的群桩效应是研究被动桩的重要问题。运用岩土数值计算程序FLAC3D,对土体沿深度发生均匀侧移,桩基两端简化为铰接的刚性双桩基础(桩中心连线与土体位移方向平行)进行研究。土体采用摩尔-库伦本构关系,桩基采用线弹性本构关系,桩土之间建立接触面。结果表明,在土位移增加的过程中,两桩侧向土压力均小于单桩,呈近桩大、远桩小。在浅层土体,加筋效应很小,但遮拦效应明显。在深层土体内,加筋和遮拦效应都很显著,p—δ曲线形状与单桩明显不同,在经历较短直线增长后,沿曲线增长至极限土压力,达到桩侧极限土压力所需的桩土相对位移量明显增加,当桩间距增长至6 D,群桩效应基本消失。最后与室内模型试验所得到的桩侧极限土压力群桩效应系数进行了对比分析。

The group effect of the lateral soil pressure acting on the passive pile shafts was an important problem.Using the explicit finite difference code FLAC3 D,the group effect of the lateral soil pressure along the pile shaft for coupled passive stiff piles（center to center＂joining＂line being in the directon of applied soil movements）with pined-head and pined-tip condition and uniform soil movement was investigated.The Mohr-Columb elastic-plastic constitutive model was employed to model the non-linear stress-strain soil behaviour and the coupled piles were assumed to have linear elastic behaviour and the interface model incorporated in FLAC3 Dcode has been used to simulate the soil/pile contact.The results given by the numerical analysis indicated that the lateral soil pressures on the coupled passive piles were lower than those for single passive piles,the lateral soil pressure on the＂near＂pile was higher than those for＂far＂pile.In the shallow soil,The reinforcing effect was not obvious,but the shadowing effect was remarkable.In the deep soil,the reinforcing effect and the shadowing effect were all remarkable.The shape of the p-δcurves was different from the single pile.After a short linear rise,the lateral soil pressure experienced a non-linear growth before achieving the limiting soil pressure.The magnitude of relative displacement to mobilize the limiting soil pressure was more than those for single passive piles.When the pile spacing increased to 6times the pile diameter,the group effect became very small.In the end,the group factors of ultimate soil pressure for various pile spacings were summarized and compared with the result of the laboratory model test in the literature.