桩基非对称局部冲刷条件下土体应力变化解析解

Analytical Solution of Soil Stress Variation Under Condition of Asymmetric Local Scour of Pile Foundation

传统桩基局部冲刷坑模型主要采用对称形态的坑体来分析,然而实际问题中局部冲刷坑体常为非对称,这使得桩基处于更不利的状态。评价桩基承载力的关键之一是合理计算冲刷坑造成的土体应力状态变化。而对于桩周形成非对称冲刷坑时土体应力变化,目前仍然没有较为完善和严格的理论分析方法。针对该问题,根据已有试验得到的非对称局部冲刷坑形态,提出非对称冲刷坑内土体应力计算的平面应变简化模型;并基于弗拉曼解在半无限空间中的应用,将冲刷坑以上土体看做荷载并引起土体内应力重分布,得到非对称冲刷坑下土体应力分布计算的平面应变解析解。通过有限元中的"生死单元法"模拟非对称局部冲刷坑的形成过程,并将有限元得到的冲刷坑内土体应力结果与解析解计算结果进行对比,验证解析解的正确性。随后基于该方法考虑桩尺寸的影响,得到非对称局部冲刷坑形成后桩周土体的垂直及水平有效应力计算方法,并与有限元计算结果进行了对比。结果表明:在考虑桩尺寸时,解析解计算结果略保守。在此基础之上,对非对称冲刷坑参数的敏感性进行分析,指出桩上、下游侧冲刷深度差值对桩周土体的应力影响较大,得到了非对称冲刷坑下桩周土体的垂直有效应力及水平有效应力差的变化规律,研究结果可为工程设计提供参考。

The conventional local scour hole of a pile foundation primarily adopts symmetrical holes for analysis. Local scour holes are often asymmetric in engineering practice;making pile foundation more unfavorable. Calculating the change in soil stress caused by the scour is crucial in evaluating the bearing capacity of the pile foundation. However, no perfect and strict theoretical analysis method exists for calculating soil stress when an asymmetric scour hole is formed. Based on the shape of the asymmetric local scour hole obtained from existing experiments, a simplified plane strain model for calculating the soil stress in an asymmetric scour hole is proposed. This study proposes an analytical solution for calculating the stress distribution under local scour conditions, which is based on Flamant’s solution in a semi-infinite space, and considers the soil above the scour hole as a load. The result was verified by comparisons with the FEM results. Based on this method, the influence of the pile diameter is considered and compared with the FEM results, which indicates that the theoretical results of this study are slightly conservative. The variations in the vertical effective stress and the difference in the horizontal stress of the soil are discussed. This could provide a reference for practical engineering applications.