排水刚性桩处置饱和砂土地基的原位试验与抗液化机理研究

Sand liquefaction will cause a lot of damage to the pile foundation during strong earthquakes. The main reason is that the excess pore water pressure of the soil cannot dissipate in time during the earthquake. The constraint condition of the pile is lost, which can cause the damage of the pile body and the superstructure. Drainable rigid pile is a new pile technique which combines a vertical drainage with a rigid pile. It has been applied in Chinese engineering. However, the research of its mitigation theory is far from with the demand of engineering application. In this project, the reinforcement mechanism of drainable rigid pile on liquefiable soils will be analyzed through the explosion field tests and numerical simulations. Firstly, the field explosion tests on the single piles and pile groups will be carried out. The regularity of the generation and dissipation of excess pore water pressure in the surrounding soils will be analyzed. The relationship between the space-time distribution of the excess pore water pressure with the drainage water in the foundation will be established. Secondly, based on the tests, the pile-soil interaction model considering the drainage effect will be proposed to establish the theory of the dynamic interaction between the drainable rigid pile and surrounded soil. Finally, based on the numerical simulation of typical earthquakes, analyses of the mitigation effect of the drainable rigid pile will be done, and the calculation method of the drainable rigid pile in the liquefiable saturated sand foundation will be obtained. Research results will expand the application of the drainable rigid pile technique in liquefiable sandy foundation, which is of great importance to seismic prevention and disaster mitigation for our country.

强震时砂土地基液化会产生大量桩基震害现象。究其原因，主要是桩周土体的超静孔隙水不能及时排出，使得桩周丧失约束，从而引起桩身及上部结构的破坏。排水刚性桩是一种将排水体与刚性桩相结合的新桩型，目前已在国内工程中予以应用，但其加固理论和计算方法研究还远不能满足工程应用需求。本项目以排水刚性桩为研究对象，采用爆炸液化原位试验为技术手段，对排水刚性桩处置饱和砂土地基的加固机理开展研究。首先，通过单桩和群桩基础的原位爆炸液化试验，分析排水刚性桩周围土体超静孔隙水压力的增长和消散规律，建立地基中孔压时空分布与排水体之间的对应关系；其次，提出考虑桩侧排水作用的桩土接触模型，建立排水刚性桩与液化土体的动力相互作用理论；最后，基于典型震害的数值模拟，分析排水刚性桩的抗液化加固效果，提出饱和砂土地基中排水刚性桩的计算方法。研究成果将为砂土地基提供新的抗液化加固方法，对我国防震减灾具有重要的参考价值。

排水刚性桩是一种将竖向排水体与刚性桩相结合的新桩型，在保持刚性桩的高承载力的同时，通过沿桩身分布的竖向排水体为地震作用下桩周液化土体提供有效排水通道，达到减轻桩基及上部建筑物震害的目的。本项目围绕“排水刚性桩处置可液化砂土地基的原位试验与抗液化机理研究”开展研究，完成的主要工作包括：（1）基于现场试验，实测了单根及相邻排水刚性桩沉桩过程中桩周土体超孔隙水压力响应。（2）通过有限元三维软件建立了排水刚性桩挤土效应计算模型，提出了实现排水刚性桩挤土扩张的新方法。（3）利用爆炸作用获得大面积液化场地，在液化场地中开展排水刚性桩单桩试验研究，对比未设置排水体的刚性桩与设置不同排水体的排水刚性桩在液化地基中的动力响应。（4）对比普通桩与排水刚性桩的现场试验结果，在此基础上开展了研究排水刚性桩作用机理和既有桩基工程加固效果的室内试验。（5）基于排水刚性桩与桩周土体的桩土相互作用理论，开展典型液化震害下排水刚性桩加固可液化砂土地基数值模拟研究，并基于排水刚性桩抗液化加固效果的评价指标，从排水体和桩体两个方面对抗液化加固效果进行分析，其中排水体考虑其通水特性、几何尺寸、布置方式；桩体考虑其桩长、桩间距、群桩布置形式等参数的影响，提出饱和砂土地基中排水刚性桩加固的计算方法。依托本项目发表（含录用）学术论文14篇，其中SCI检索论文8篇，EI检索论文12篇。获得重庆市自然科学一等奖1项（排名：3/6）。获得发明专利授权2项。项目负责人入选2019年教育部长江学者（青年学者），2022年入选重庆市“巴渝学者”讲座教授，项目研究成果拓展了排水刚性桩在饱和砂土地基中的应用，对我国广大砂土地区的防震减灾工作提供重要技术支持，具有重要的理论意义和应用价值。