挤密效应对砂土中水平受荷桩影响的数值研究

Numerical study on the influence of installation effect on laterally loaded piles in sand

为研究桩贯入砂土地基中导致的挤密效应对桩基水平承载能力的影响,建立数值模型模拟桩的压入过程和水平承载过程并分析桩的响应.结合任意拉格朗日-欧拉(arbitrary Lagrangian-Eulerian,ALE)技术和与状态相关的剪胀性砂土本构模型,对桩的贯入全过程进行模拟,并与模型试验进行对比验证.通过坐标转换与插值将轴对称ALE模型的土体状态数据传入三维拉格朗日有限元模型中,进行水平加载研究.为分析挤密效应的影响,同时模拟了无挤密效应时的水平受荷桩.结果表明,桩贯入后的挤密效应与砂土相对密度有关,在相对较密的砂土中会出现浅层砂土被挤松的现象,同时桩的贯入提高了砂土的水平应力;挤密桩的土水平抗力与桩水平位移曲线在松砂中普遍高于无挤密桩,在密砂中的浅层处则相反;挤密效应对松砂中长径比较小的桩的水平承载力有较大的提高作用,同时会降低密砂中长桩的承载力;由于挤密效应影响的水平承载力变化率与砂土的相对密度呈负相关,在长桩中两者有较强的线性关系.研究可为预测挤密桩的水平承载力提供参考.

In order to study the influence of the installation effect caused by pile penetration into a sand foundation on the pile horizontal bearing capacity,we establish a numerical model to simulate the penetration process and the horizontal loading process of the pile and analyze the response of pile.The whole process of pile penetration is simulated using the arbitrary Lagrangian-Euler(ALE)technology and a state-dependent dilatancy sand constitutive model,and compared with the model test.Through coordinate conversion and interpolation,the soil state data of the axisymmetric ALE model is transferred to a three dimensional Lagrangian finite element model for horizontal loading research.In order to quantitatively study the influence of the installation effect,the laterally loaded pile without the installation effect is simulated simultaneously.The results show that the compaction effect after pile penetration is related to the relative density of sand.Sand loosening has been observed in shallower locations for piles in relatively dense sand.The penetration of piles also improves the level of lateral soil stress.In loose sand,the lateral soil resistance-pile displacement curves of piles with installation effect are generally higher than that without installation effect.However,opposite observations have been made for the shallow layers of dense sand.The installation effect can greatly improve the lateral bearing capacity of the relatively short piles in loose sand,and on the contrary,it reduces the lateral bearing capacity of long piles in dense sand.The change rate of the lateral bearing capacity after considering the installation effect is negatively correlated to the relative sand density,which shows a strong linear relationship for long piles.This study can provide reference for predicting the horizontal bearing capacity of a displacement pile.