Effects of soil heterogeneity on pile foundations under seismic loads

尽管设计中采用了较大的安全裕度，但饱和土的地震液化仍然是造成深地基地震破坏的主要原因。本提案概述了一项结合实验和数值研究，旨在解决液化土壤中桩的破坏机制和相互作用力等一系列尚未得到解答的问题，并为行业提供深地基抗震设计的可靠工具和指导方针。今天，人们都很清楚，即使在不同的地质层中，土壤的性质也会因地而异。这种天然土壤非均质性对土壤液化和土桩相互作用的影响也将被讨论。在这方面，最近的理论研究发现了这种天然土壤在地震荷载下的一个非常有趣的行为，这可能对地震岩土工程的设计实践产生重大影响。迄今为止，工程实践界还没有实验验证来帮助认识、量化和接受非均质土的上述行为。在本研究计划中，提出了一系列用于随机非均质土桩基地震分析的原始离心实验，以研究理论研究中确定的非典型土行为并量化其对深基础的影响。基于实验结果，将对最先进的用于土-结构系统动态有效应力分析的有限元代码进行校准，并用于扩大实验程序的范围。然后，实验和数值结果将用于开发、校准和验证一个计算有效的工具，用于桩基的地震分析，可随时用于当前的设计应用。最后，新工具将用于系统的数值研究，为广泛的现场情况和地震荷载提供设计指导。用于实验的土壤材料和理论发展的例子将从不列颠哥伦比亚省的弗雷泽河三角洲选择，这是一个人口稠密的地区，极易受到地震灾害和土壤液化的影响。

Seismic induced liquefaction of saturated soil is still a major cause of earthquake damage to deep foundations, in spite of relatively large safety margins used in design. This proposal outlines a combined experimental and numerical study aimed at addressing a series of questions regarding failure mechanisms and interaction forces for piles in liquefying soil that have not been answered yet, and at providing the industry with a reliable tool and guidelines for seismic design of deep foundations. It is well understood today that soil properties vary from one point to another even within geologically distinct layers. The effects of this natural soil heterogeneity on soil liquefaction and soil pile interaction will also be addressed. In this respect, recent theoretical research identified a very interesting behaviour of such natural soils subjected to seismic loads that is likely to have significant influence on design practices in earthquake geotechnical engineering. To date, there is no experimental verification available to the practicing engineering community to help in recognizing, quantifying and accepting the above-mentioned behavior of heterogeneous soils.   A series of original centrifuge experiments for seismic analysis of pile foundations in randomly heterogeneous soil are proposed in this research program to investigate the atypical soil behaviour identified in theoretical studies and to quantify its effects on deep foundations. A state-of-the-art finite element code for dynamic effective stress analysis of soil-structure systems will be calibrated based on the experimental results and used to expand the scope of the experimental program. Both experimental and numerical results will then be used to develop, calibrate and validate a computationally effective tool for seismic analysis of pile foundations, readily available for current design applications. Finally, the new tool will be used in a systematic numerical study to provide design guidelines for a wide range of field situations and seismic loads. The soil materials for experiments and the examples for theoretical developments will be selected from the Fraser River Delta in British Columbia, a densely populated region highly vulnerable to earthquake hazards and soil liquefaction.