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

可液化土壤中的桩基在地震期间继续失效，尽管在设计时具有所需的抗轴向承载能力(轴阻和端部承载)和横向荷载弯曲的安全系数。这些横向荷载产生于上部结构的惯性和流经桩身的土体的运动荷载(横向扩展)。最近的研究发现，这种设计方法存在一个根本性的疏漏。基本上，当地基液化时，其侧向支承的减少允许细长桩在轴向荷载下屈曲：在目前的设计中，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)。其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，并开发分析方法以更好地考虑轴向载荷的影响。桩的分析一般采用非线性文克勒地基上梁(BNWF)模型或p-y模型，因为它简单、数学方便且能考虑土体的非线性。本质上，土被模拟为一组沿桩分布在不同位置的p-y弹簧，其中p是指在一定深度处土体对桩变形y的反作用。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了，但对于可液化的土壤，该行业仍然缺乏有前途的p-y曲线。本研究旨在研究液化土桩的水平荷载，了解桩与液化土间的相互作用现象，并基于高质量模型试验数据的反分析、液化土单元试验、数值模拟和桩基础性能的实例记录，提出液化土地基的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.