Study of lateral-pile-soil-interaction (LPSI) in seismically liquefiable soils

可液化土中的桩基在地震期间继续破坏，尽管其设计具有抗轴向承载能力（轴阻力和端承）和侧向荷载弯曲的安全系数。这些侧向荷载是由上部结构的惯性和流过桩基的土体的运动荷载（侧向扩散）引起的。最近的研究发现了这种设计方法中的一个基本遗漏。从本质上讲，当地面液化时，侧向支撑的减少使细长桩在轴向荷载下发生屈曲，在当前设计中忽略了这种屈曲机制或P-delta效应（P为轴向荷载，delta为桩头位移）。实际影响可能是深远的，需要重新评估可液化土壤中的现有结构，以及开发分析方法以更好地考虑轴向载荷的影响。由于其简单、数学上的方便性和考虑土体非线性的能力，通常采用非线性温克勒地基梁模型或p-y模型对桩进行分析。本质上，土壤被建模为沿桩在离散位置分配的一组p-y弹簧，其中‘p’表示在一定深度处土体对‘y’桩变形的反应。虽然砂（非液化条件下）、软粘土、硬粘土的p-y曲线已经建立，但液化土的p-y曲线仍然缺乏。本课题旨在通过高质量模型试验数据反分析、液化土单元试验、数值模拟和桩基性能案例记录，研究液化土中桩侧荷载，了解桩与液化土相互作用背后的现象，提出液化土的p-y曲线。

Pile foundations in liquefiable soil continue to fail during earthquakes despite being designed with required factor of safety against axial load bearing capacity (shaft resistance and end-bearing) and bending due to lateral loads. These lateral loads arise from the inertia of superstructure and kinematic loading of soil flowing past the pile (lateral spreading). Recent research discovered a fundamental omission in this design methodology. Essentially, when ground liquefies its reduction in lateral support allows slender piles to buckle under their axial load: there is an omission of this buckling mechanism or the P-delta effect (P is the axial load and delta is the pile head displacement) in the current design. The practical implications could be far reaching, requiring reassessment of existing structures in liquefiable soils as well as developing analysis methods to take better account of the effects of axial load. Piles are typically analysed using a Beam on Nonlinear Winkler Foundation (BNWF) model or p-y model due to its simplicity, mathematical convenience and ability to incorporate nonlinearity of soil. Essentially, the soil is modelled as a set of p-y springs assigned along the pile at discrete locations, where 'p' refers to the soil reaction to the pile deformation 'y' at a certain depth. While the p-y curves for sand (under non-liquefied condition), soft clay, stiff clay are well established, the profession still lacks a promising p-y curve for liquefiable soil. This research proposal aims to study the lateral loading of piles in liquefied soil, to understand the phenomena behind the interaction between pile and liquefied soil and to propose a p-y curve for liquefied soil based on back analysis of high quality model test data, element tests on liquefied soil, numerical modelling, and case records of pile foundation performance.