复合地基性状及荷载作用尺寸效应有限元分析

【作者】 朱东海；

【导师】 白良；

【作者基本信息】 昆明理工大学 ， 道路与铁道工程， 2002， 硕士

【摘要】 复合地基法是近年来对软土地基处理应用极为广泛的一种，目前，复合地基的理论落后与实践的发展，本文利用有限元的方法并结合现场荷载试验来研究复合地基的一些特性。 在进行复合地基性状的研究中，通过建立不同的有限元模型，研究桩长、桩体刚度、面积置换率对均质地基复合地基桩身应力、桩身侧摩阻力传递规律、变形特性和承载力的影响。同时，分析单桩复合地基、群桩复合地基荷载传递规律及变形特性的差异，群桩复合地基中内桩、边桩荷载传递规律的差异问题。分析表明群桩复合地基具有群桩效应问题，其性状与单桩复合地基有很大的不同。 本文从复合地基具有群桩效应现象入手，利用有限元来研究大面积复合地基、单排群桩复合地基、双排群桩复合地基荷载试验的尺寸效应问题，并用现场荷载试验实例来验证本文分析方法的可行性。得到确定大面积复合地基承载力的荷载试验中，一般测试4根桩所处理的面积，测得的承载力就能较好地接近在群桩效应下的结果，而确定单排或双排群桩复合地基的承载力，单桩或双桩复合地基荷载试验的结果便行。并对利用荷载试验的沉降预测工后沉降进行一些探讨。 同时，分析软弱夹层在不同位置以及不同厚度对复合地基荷载传递规律和变形特性的影响，得出保护硬壳层和桩端选择较好持力层的理论依据。 最后，基于水泥土搅拌桩复合地基的特性，以作用在弹性半空间的集中力为前提的Mindlin解应用于复合地基的变形计算中，提出一种较为实用的变形计算方法。更多还原

【Abstract】 With the prosperity of Chinese economy, there are infrastructures in large scales, and the techniques to treat soft soil have developed quickly at the same time. Especially composite foundations are used widely. But the theory is behind the practice in this field. Based on the FEM analysis and load tests in site, some performances of composite foundation are studied.In this research how the length of pile, the rigidity of pile and area replacement ratio of composite foundation affect the stress in the pile, the siding friction transfer law of pile and the deforming characteristics and bearing capacity of the entire foundation is studied. Meanwhile the load transfer laws and the deforming characteristics of single pile composite foundation and group piles composite foundation are researched. Additionally, the deference between the load transfer laws of the inside piles and the side piles and the effect of group piles are analyzed.In the engineering the static load test usually is used to determine the bearing capacity of composite foundation, but the relative specifications in the "The criterion of building foundation treatment(JGJ79-91)" are not so clear. Starting from the effect of group piles in the composite foundation, the size effect in the load test of large area composite foundation, composite foundation of single row piles and composite foundation of double rows piles are researched through FEM analysis. And these are verified by load test in site to validate the conclusion that the testing result on four piles area is closed to the result with the group piles effect in large area composite foundation and to determine the bearing capacity of composite foundation of single row piles and double rows piles, the result from single pile composite foundation is acceptable. Moreover the question of predicting settlement after the engineering finished based on the settlement of load test is discussed.Meanwhile, how the soft interlayer of different place or different thickness affects the load transfer laws and the deforming characteristics of composite foundation are studied, to get the academic basis of the opinion that the hard surface layer should be protect to be utilized and the bearing layer should be good soil.In the end, according to the characteristics of cement mixing piles composite foundation, a practical settlement concluding method for composite foundation is recommend based on theMindlin solution for the centralized force in a half elastic space.更多还原