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

在可液化土壤中的桩基础在地震期间继续失效，尽管其设计具有针对轴向承载能力（轴阻力和端部承载）和由于横向载荷引起的弯曲的所需安全系数。这些横向荷载来自上部结构的惯性和流过桩的土壤的运动荷载（横向扩展）。最近的研究发现了这种设计方法中的一个基本遗漏。基本上，当地面变形时，其横向支撑的减少允许细长桩在其轴向载荷下屈曲：在当前设计中省略了这种屈曲机制或P-δ效应（P是轴向载荷，δ是桩头位移）。实际影响可能是深远的，需要重新评估现有的结构在可液化土壤以及开发分析方法，以更好地考虑轴向载荷的影响。桩通常使用非线性Winkler地基梁（BNWF）模型或p-y模型进行分析，因为其简单，数学方便且能够纳入土壤的非线性。从本质上讲，土壤被建模为一组p-y弹簧，这些弹簧沿桩沿着分布在离散位置，其中“p”是指土壤对桩变形“y”在一定深度处的反应。虽然砂土（在非液化条件下）、软粘土、硬粘土的p-y曲线已经很好地建立起来，但该专业仍然缺乏一个有前途的可液化土壤的p-y曲线。本研究计划旨在研究液化土中桩的侧向荷载，了解桩与液化土之间相互作用的现象，并基于高质量模型试验数据的反分析，液化土的单元试验，数值模拟和桩基性能的案例记录，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.