【作者】 丁桂伶；

【导师】 王连俊；

【作者基本信息】 北京交通大学 ， 水文地质与工程地质， 2010， 博士

【摘要】 CFG桩复合地基在新建的京津城际、武广客运专线、京沪高速铁路等时速为350km/h高速铁路的软基处理中得到了广泛的应用。CFG桩复合地基作为软土处理的一种手段,具有沉降量小、承载力高、稳定快、工期短等特点,取得了较好的经济效益和社会效益。但是,目前规范中有关CFG桩复合地基设计方法及承载力的计算均是针对工民建提出来的,将其直接应用到高速铁路柔性荷载下复合地基中尚存在许多难以解决和改进的问题。基于柔性荷载下CFG桩复合地基的作用机理、计算理论等尚未成熟,本论文通过现场试验、理论分析和数值计算等手段,系统地对京沪高速铁路试验段桩筏和桩网复合地基沉降及受力特性、柔性载荷试验原理及方法、CFG桩复合地基三维数值模拟计算及优化方法进行了深入的研究和探讨,主要研究内容和成果如下：(1)在路基填筑过程中桩帽网复合地基沉降量大于桩筏复合地基,但桩帽网复合地基中的桩土应力比和桩荷载分担比明显小于后者,且经济造价也低于后者；(2)通过自行研制的现场静力柔性载荷试验设备,利用橡胶板模拟高速铁路填筑过程对复合地基桩及土体柔性施加荷载的方式,首次提出了采用柔性载荷试验确定高速铁路复合地基承载力的方法；(3)通过现场对CFG桩单桩复合地基进行柔性载荷试验发现随着荷载的增加复合地基中土体的荷载发挥系数先于桩到达1.0,说明柔性荷载下CFG桩复合地基的破坏模式是土体先产生破坏,然后复合地基破坏,这与刚性基础不同；(4)现场对带帽和无帽的CFG桩复合地基在不同褥垫层厚度情况下进行了柔性载荷试验,分析研究了褥垫层对复合地基桩及桩间土的沉降变形、荷载分担特性、荷载发挥系数的影响,认为褥垫层厚度取20cm时较为合理；(5)建立了CFG桩群桩复合地基三维数值计算模型,应用有限元计算软件分析了不同桩(帽)强度、桩径、桩长、桩间距、桩帽直径、褥垫层厚度等因素对CFG桩复合地基沉降变形与受力特性的影响；(6)提出柔性荷载下CFG桩复合地基优化设计的原则与思路,并按照路基工后沉降与桩帽、桩间土的强度利用率要求,对京沪高速铁路的设计方案进行了优化。更多还原

【Abstract】 CFG pile composite foundation has been widely used in treatment of soft foundations of such high-speed railways as Beijing-Tianjin Intercity Rail Transit, Wuhan-Guangzhou passenger transport line and Beijing-Shanghai high-speed railway with 350km/h. Being one of soft foundation treatment means, CFG pile composite foundation has such characteristics of less settlement, high bearing capacity, fast stability and short-period project, etc. Tremendous economic and social benefits have been achieved. However, the design method of CFG pile composite foundation and computing method of bearing capacity are all based on the civil buildings in standards. It usually has great differences with the results of which are used in the computing of high-speed railway composite foundation under flexible load. In view of the immaturity of the action mechanism and computing theory of CFG pile composite foundation under flexible load, the settlements and stress characteristics of pile-raft and the pile-net composite foundation, the fundamental principal and methods of flexible load test and three-dimensional numerical model and optimization method of CFG pile composite foundation in Beijing-Shanghai high-speed railway are studied deeply in this paper through on-site testing, theoretical analysis, numerical analysis and optimization tools. Corresponding study achievements are presented as follows:(1) The settlement of pile-cap-net composite foundation is more than that of pile-raft composite foundation during the building of embankment. However, the stress and load sharing ratio of pile and soil of the former are more obviously smaller than the latter, as well as economical cost is also lower than the latter.(2) The computing method of CFG pile composite foundation bearing capacity of high-speed railway is firstly put forward by means of flexible load test. The test uses rubber plank to simulate the flexible load acting to the pile and soil of composite foundation during building process with the flexible load test equipments developed by ourselves.(3) The load developing coefficient of soil is the first to arrive at 1.0 with the increase of load through on-site flexible test of CFG single pile composite foundation. The results prove that the soil body is destroyed more rapidly than composite foundation under flexible load which is different with rigid foundation.(4) The influence of cushion on the settlement and deformation, load sharing behaviors and developing coefficient of pile and soil between piles are studied through CFG pile composite foundation flexible load test with different cushion thickness. It is found that the bearing capacity is more suitable for playing when the thickness of cushion is 20cm.(5) Three dimensional numerical model of CFG pile group composite foundation is established through finite element analysis software. And the influence of different pile (cap) strength, pile diameter, pile length, pile spacing, pile cap diameter and cushion thickness on the deformation and force characteristics of CFG pile composite foundation are studied after then.(6) The principle of optimal design and ideas of CFG pile composite foundation under flexible load is proposed. And the design of the Beijing-Shanghai high-speed railway is optimized in accordance with post-construction settlement of subgrade and the utilization requirements of pile caps and soil between piles.更多还原