基于耦合欧拉-拉格朗日方法的砂土中静压桩挤土效应数值模拟

Numerical simulation of compaction effect during pile jacking in sand based on the coupled Eulerian-Lagrangian method

为探讨砂土地基中静压桩沉桩过程的挤土效应,引入Simsand砂土临界状态本构模型,采用耦合欧拉-拉格朗日(coupled Eulerian-Lagrangian, CEL)方法,模拟分析了砂土中静压沉桩过程的挤土效应。基于相关试验数据校定本构模型参数,利用模拟离心机沉桩试验,验证数值模型的准确性。结果表明,挤土效应的影响区域直径随着桩尖角度和砂土相对密度的增大而增大,压入过程中,平底桩的挤土效应倾向于竖向向前,增大了土体阻力。桩基压入引起近地表土层发生隆起,密砂地层的隆起较松砂地层显著。随着深度增加,桩周土体的竖向位移由隆起变为向下移动,且趋于稳定,密砂中发生的侧向位移大于松砂地层。挤土效应的影响区域直径随桩端竖向向下方向迅速衰减,随桩端竖向向上方向发生小幅度减小,在密砂中沿径向方向呈现先增大后减小的趋势。

In order to explore the soil squeezing effect of the hydrostatic pile sinking process in sandy soil foundation,the Simsand critical state constitutive model of sand was introduced,and the coupled EulerianLagrangian(CEL)method was used to simulate and analyze the hydrostatic pile sinking process in sandy soil.The Sand parameters of the Simsand model werecalibrated based on published laboratory test data,which wereused in the simulation of centrifuge model tests of pile penetration in sand.The numerical model was verified by comparing the simulation results and the model test data.Overall,the influence range of pile jacking became larger with increases of the tip angle of a pile and the realative density of sand,the soil squeezing effect of the flat-bottom pile was more inclined to vertical forward in the process of pressing,thus mobilizing more soil resistance.Pile-foundation compression caused uplift in the near-surface soil layer,and the uplift of dense sand stratum was more significant than that of loose sand stratum.With the increase of depth,the vertical displacement of soil around the pile changed from uplift to downward movement and tendedto be stable,and the lateral displacement in dense sand was greater than that in loose sand.The diameter of the area affected by the soil squeezing effect decrease drapidly with the vertical downward direction of the pile end,decreased slightly with the vertical upward direction of the pile end,and increasedfirst and then decreased along the radial direction in dense sand.The influence range of pile jacking decreased repeadly and moderately along the downward and upward direction from the pile tip,repepectively,and increased first and then decreased along the radial direction.