压桩过程中静压桩挤土位移的动态模拟和 实测对比研究

 圆孔扩张法及应变路径法由于土体的大变形和桩土界面摩擦接触问题而难以模拟动态的压桩过程，数值模拟法能够考虑到土体的本构关系、大变形和桩土的相互作用等诸多因素的影响，因而在静压桩挤土效应方面得到了广泛的应用。采用合适的土体屈服准则及有限变形理论，通过在桩土界面设置接触以及在桩顶施加位移荷载建立了能够实现动态压桩过程的有限元模型。利用得到的有限元模型模拟了沉桩产生的水平及竖向挤土位移场，讨论了动态压桩过程对沉桩挤土位移场的影响，并和现场实测进行了对比。研究结果表明，挤土位移场动态模拟结果与实测值相一致，且能反映土性的变化情况；在动态压桩过程中，水平向的挤土位移随着压桩深度的增加而增大，竖向挤土位移随着压桩深度的增加浅层土体表现为隆起增加，而深层土体表现为下沉量增加。挤土位移的最大值与压桩深度存在滞后效应，因此在压桩过程中要给以足够的重视。

COMPARATIVE STUDY OF DYNAMIC SIMULATION FOR COMPACTING DISPLACEMENT OF JACKED PILE AND IN-SITU TEST

Due to soil large deformation and friction between pile and soil，cavity expansion method and strain path method can not simulate the dynamic penetration process of jacked pile；but finite element method has been widely used in the penetration process，solving the soil constitutive relationship，large deformation and interaction between pile and soil. An appropriate finite element model is given that accords with the actual process of jacked pile. This model adopts the rational constitutive model of soil and finite deformation theory. Through pile-soil interaction and displacement loading on pile top，the dynamic pile-sinking process is simulated. Horizontal and vertical displacement fields are studied through the finite element model. The effects of displacement fields caused by dynamic pile-sinking procedure are discussed；and moreover，the simulation results are compared with field test. The results show that compacting displacements are in accord with measured results；and further，change of compacting displacement can reflect the change of soil characteristic. During the installation of jacked pile，the horizontal compacting displacements increase with the increase of pile penetration depth；but for the vertical compacting displacements，the heave increases in shallow soil layers and settlement increases in deep soil layers with the penetration depth increasing. The maximum compacting displacement delays the pile-sinking depth，so it is necessary to put great emphasis on dynamic pile-sinking process.