液化场地桥梁群桩-土耦合体系强震反应分析

Strong Seismic Response of Pile Group-soil Coupling System in Liquefied Ground

摘要:

针对振动台试验，采用u-p形式控制方程表述饱和砂土的动力属性，选用土的多屈服面塑性本构模型刻画饱和砂土和黏土的力学特性，引入非线性梁-柱单元模拟桩，建立试验受控条件下液化场地群桩-土强震相互作用分析的三维有限元模型，并通过试验结果验证数值建模途径与模拟方法的正确性。以实际工程中常用的2×2群桩为例，建立桩-土-桥梁结构强震反应分析三维有限元模型。基于此，针对不同群桩基础配置对液化场地群桩-土强震相互作用影响展开具体分析。对比发现，桩的数量相同时，桩排列方向与地震波输入方向平行时比垂直时桩基受力减小5%~10%，而对场地液化情况无明显影响；相同排列形式下，三桩模型中土体出现液化的时间约比双桩模型延缓5 s，桩上弯矩和剪力减小33%~38%。由此可见，桩基数量增加，桩-土体系整体刚度更大，场地抗液化性能显著，桩基对上部桥梁结构的承载性能明显增强，其安全性与可靠性更高。这对实际桥梁工程抗震设计具有一定的借鉴意义。

Abstract:

A three-dimensional finite element model was established for a shaking table test of dynamic pile group-soil interaction. Governing equations of u-p formulation were used to describe the dynamic properties of saturated sand. We choose a plastic multi-yield surface constitutive model to describe the dynamic properties of saturated sand, and a nonlinear beam-column element was used to simulate the pile in this model. The results of the test verify the validity and effectiveness of the numerical model. In an experiment using a 2×2 pile group, a three-dimensional nonlinear finite element model of soil-pile-bridge structure interaction was established. Based on this 2×2 pile group model, with a 2 piles in row pile group model (2PR) and a 2 piles in parallel pile group model (2PP), a 3×3 pile group model (with a 3PR pile group model and a 3PP pile group model) have been expended. Based on different configurations of pile group foundations, an analysis of soil-pile group interaction in liquefied ground was made. When using the same number of piles and a pile array direction parallel to the direction of seismic wave, stress is reduced by 5%~10%. However, there are few obvious effects on site liquefaction conditions. Under the same parallel array of piles, in comparison to the two-pile model, the three-pile model ground-liquefaction time results in delays of 5 s, and pile bending moment and shear force decreases 33%~38%. With an increase in the number of piles, the ground-liquefaction time is delayed, and the stress of pile body decreases. The results of this study will be of significant use for bridge engineering design.