多元桩加固可液化饱和粉土地基作用机理与变形特性研究

Gravel pile composite foundation is one of widely used anti-liquefaction reinforcement measures. In recent years, in order to meet the actual needs, treatment method of gravel pile and other types of pile combination is often used in engineering. At present, the research of mechanism,dynamic deformation characteristics and deformation characteristics after seismic of multi-element composite foundation composed by different types of piles is still at the initial stage. The Yellow River delta liquefiable saturated silt treated by gravel pile and CFG pile is the research object of this project. Through experiments and numerical simulation, the seismic liquefaction mechanism and dynamic characteristics of the Yellow River delta saturated silt will be studied,and the dynamic constitutive model of saturated silt will be established，the second development of finite element software will be finished; the mechanism of multi-element composite foundation will be studied, such as densification effectiveness, drainage effectiveness, pile body effectiveness and coupling effectiveness; the influence of pile design parameters, layout of piles and other factors on anti-liquefaction nature , dynamic deformation characteristics and deformation characteristics after seismic of multi-element composite foundation will be discussed.At last,the criterion of liquefaction reflecting pile body effectiveness will be established, the settlement of multi-element composite foundation after seismic will be predicted,and the pile economic ratio reference value of gravel pile and CFG pile treating liquefiable saturated silt ground will be given.This study will be helpful to enrich the design theory of composite foundation, and provide theoretical basis for optimum design of multi-element composite foundation.

碎石桩复合地基是广泛采用的抗液化加固措施之一。近几年，为了满足实际需要，工程中常采用碎石桩与其他类型桩相结合的处理方法。目前，对由不同类型桩构成的多元复合地基的作用机理、动变形特性和震后变形特性的研究尚处于起步阶段。本项目以碎石桩和CFG桩构成的多元复合地基加固黄河三角洲可液化饱和粉土为研究对象，通过试验和数值模拟，研究黄河三角洲饱和粉土的地震液化机理和动力特性，建立饱和粉土的动本构模型，完成有限元软件的二次开发；研究多元复合地基的作用机理，包括桩体的加密、排水和桩体效应以及各效应的相互耦合作用；研究桩体设计参数、布桩方式等因素对多元复合地基抗液化效果、动变形特性和震后变形特性的影响。最后，建立体现桩体效应的多元复合地基液化判别标准，对多元复合地基的震后沉降进行预测，给出碎石桩与CFG桩加固可液化饱和粉土的型桩经济配比参考值。本研究将有助于丰富复合地基的设计理论，为其优化设计提供理论依据。

近年来，为了满足实际工程需求，常采用碎石桩与其他类型桩相结合的处理方式，这样既减轻了地基的液化又提高了地基承载力并减小了地基沉降量。目前，对由不同类型桩构成的多桩型复合地基的抗液化性能的研究尚处于起步阶段。我们针对碎石桩和CFG桩构成的多桩型复合地基加固黄河三角洲可液化饱和粉质土问题进行了深入研究。一方面，研究了黄河三角洲饱和粉土的地震液化机理和动力特性，获得了一系列研究成果，提出了黄河三角洲饱和粉土的动孔压增长模式；另一方面，对碎石桩和CFG桩构成的多桩型复合地基进行研究，设计完成了简易单向振动台系统和堆叠式剪切模型箱，获得了设计参数、布桩方式等因素对多桩型复合地基抗液化效果和动力特性的影响规律，给出了碎石桩与CFG桩加固可液化饱和粉土地基的型桩经济配比参考值。研究成果可为黄河三角洲饱和粉土的液化判别和多桩型复合地基抗液化设计提供理论参考。