【作者】 王丽坤；

【导师】 彭社琴；

【作者基本信息】 成都理工大学 ， 岩土工程， 2008， 硕士

【摘要】 近几十年,我国复合地基的应用和发展迅速,出现了许多复合地基处理方法。CFG桩复合地基法以其用材经济、施工快捷、加固效果良好等优点,在工程上得到了广泛的应用,取得了显著的经济效益和社会效益,但是其理论严重落后于工程实践。本文在现有CFG桩研究理论的基础上结合四川省南充市川北医学院附属医院住宅楼CFG桩复合地基工程实践,对CFG桩复合地基的承载特性、作用机理进行了系统的分析和研究。本文回顾了CFG桩复合地基的应用和发展情况,简要介绍了CFG桩复合地基的形成条件及其工作机理,同时在CFG桩复合地基的试验研究、理论分析方面做了一些分析和探讨。①针对该建筑场地进行了三组天然地基、十三组CFG单桩和六组复合地基载荷试验,对CFG单桩复合地基的承载力进行了分析和研究,为复合地基的设计提供参考依据;根据试验结果,得到了三种CFG单桩的荷载～沉降曲线模式,分别作了分析和探讨;在此基础上,将复合地基承载力试验结果与天然地基、单桩试验结果进行了对比分析,得到了一些结论。②CFG桩复合地基由桩—桩间土—褥垫层协同工作共同承担上部荷载。由于复合地基工作机理影响因素很多,其研究还有待于进一步深入。通过在褥垫层上下埋设压力盒,分析了桩土受力、桩土应力比随荷载的变化规律,并得到了桩间土承载力折减系数β;根据桩顶及对应褥垫层表面的受力情况,分析了褥垫层设置的作用和意义。掌握和了解了CFG桩复合地基应力分配特性。③由于CFG桩桩身弹性模量介于水泥土类桩和常规桩基之间,在荷载作用下桩身有一定的压缩量,但数值不大,这使其传递荷载的性状与水泥土类桩和常规桩基有较大的区别。通过在桩身内埋设钢筋应力计,分析了桩身轴力、侧摩阻力、桩端阻力随荷载的变化规律;另外,分析了桩侧阻、端阻荷载分担以及其荷载分担比的变化规律;与此同时,根据桩身轴力曲线以及对应的地层图,总结出了三种荷载传递模式,最终熟悉了荷载传递过程。④根据CFG桩复合基地的承载力计算模式,对CFG桩复合地基承载力的三种计算方法,即,规范法、应力比、考虑负摩擦力法,进行分析和研究,对设计参数的选取进行了讨论,并根据现场试验资料对各种计算方法进行了实例验证,得出了适合CFG桩复合地基的承载力计算方法。更多还原

【Abstract】 In the recent several years, composite foundation using and developing rapid in our country, many kinds of composite foundation processing methods appear. The CFG pile composite foundation is used in projects widely because of its economic timber, rapid construction, good reinforcement effect. Meanwhile, it has obtained good economic benefits and social benefits, but the theory analysis still falls behind the engineering practice. The thesis based on CFG pile composite foundation of the housing buildings of Chuanbei Medical College subsidiary hospital in Nanchong city Sichuan province, analyze and study the bearing character and mechanism of action of the CFG pile composite foundation.The paper reviews the application and development of the CFG pile composite foundation, introduces briefly the formation condition and action mechanism, at the same time, makes some analysis and discuss in field experiment and theory.①Some load test on site are conducted, including 3 group natural foundation、13 group single piles and 6 group composite foundations .The bearing capacity of CFG pile composite foundation are researched.All the results provide the reference for foundation design. According to the result, this paper obtains three kinds of p～s curve pattern for CFG pile, and has made the analysis and the discussion on each pattern;At besides, contrastive analysis has carried on results between the composite foundation and the natural foundation、the single pile, some meaningful conclusions are obtained.②The vertical loads on CFG pile composite foundation are beared by co-action among pile capushion, pile and the earth. Because of the multi-influencing factors, the action mechanism of CFG pile foundation is in lack of exploration. The stress between pile and soil and pile-soil stress ratio following with load are observed and analyzed through buried steel strain gauge on the piles and buried soil pressure cell on and under cushion layer, meanwhile the reduction factor of soil bearing capacity between piles is obtained.According to the force on the pile and surface of cushion, which is orresponding to the pile, the roles and significance of the cushion is studied. The character of the stress distribution is knowledged.③As the elastic modulus of CFG pile is between cement-soil pile and conventional pile, there is a certain amount of compression under the load, but not numerical, which make a different between CFG pile and cement-soil pile and conventional pile on load transfer.The change laws of axial force、lateral friction and end resistance along with the load are observed and analyzed through buried steel strain gauge on the piles. In addition, The analysis has been made on the law of load-sharing for lateral friction and end resistance.At last, theload transfer mechanism of CFG pile composite foundation is very obvious.④A few of comparison and research are carried on three computational methods, namely: standard method, stress ratio method and negative friction force method, according to the computational model of bearing capacity. Some discuss is done on parameter selection. At last, confirmation is taken on the all kinds of computational methods according to data reached through the load test on site.更多还原