【作者】 田静成；

【导师】 王贵和；

【作者基本信息】 中国地质大学（北京） ， 地质工程， 2009， 硕士

【摘要】 高层建筑林立的同时,基坑工程中遇到高层邻建的情况也越来越多,基坑侧壁实则是一个长方形的“土柱”,在土压力的计算与支护结构的设计上常有争论。在京、津两地,基坑工程经常遇到高层邻建的地基为CFG桩等刚性桩复合地基,由于复合地基不能像桩基础一样将荷载全部传递到地下较深的持力层,而是靠桩与桩间土以及下卧层相互协调变形,此时的“土柱”实为非有限土体,给支护结构设计带来更多复杂的影响因素,导致支护结构的设计没有可靠的依据。本文针对基坑工程中遇到高层邻建且其基础为刚性桩复合地基的情况,通过模型试验模拟两个基坑开挖过程,一是没有邻建的情况下排桩支护结构受力和位移变化特性;二是基坑工程有高层邻建并且邻建的基础为刚性桩复合地基的情况下,基坑开挖过程中护坡桩受力和位移变化特性以及复合地基沉降变化规律。全程监测护坡桩弯矩、土压力、桩顶位移、复合地基沉降等数据的变化,并对试验数据整理及对比分析,归纳总结,得出如下结论:⑴“土柱”—非有限土体,并不是孤立存在的,基坑支护结构、邻建复合地基以及所谓“土柱”三者之间在整个基坑开挖过程中都存在复杂的相互作用。⑵基坑没有邻建的情况下,支护结构的位移以水平方向为主,而在基坑有邻建的情况下,支护结构的位移以垂直方向为主。⑶当基坑开挖深度小于等于邻建复合地基加固深度时,支护结构受力比基坑没有邻建的情况下更均匀,数值更小,桩身强度发挥更充分,基坑更加稳定。⑷当基坑开挖深度大于邻建复合地基加固深度时,桩身弯矩值大,荷载作用形式变化频繁,荷载变化幅度大,比基坑没有邻建的情况下更不稳定。⑸在开挖过程中,复合地基对支护结构荷载作用方式的调整是自上向下进行的,调整的结果是使荷载数值变小,沿桩身分布更均匀。⑹复合地基对支护结构的应力调整的是将应力向护坡桩桩端持力层转移,持力层通过变形来消化这部分应力。此次模型试验桩端持力层即邻建复合地基下卧层,如没有“土柱”将护坡桩与邻建的复合地基隔开,邻建在开挖过程中的沉降定会加剧。更多还原

【Abstract】 As there are more and more high-rise buildings in the big cities, new foundation pits are usually nearby old high-rise construction. In this case, the wall of the pit is actually a“soil column”with a rectanglular section,we have to considered not only the stability of the“soil column”, but also the settlement of the old high building, so it is really very difficut to make a perfect design for the retaining structure of the new pit according to existing theory and methodology on soil pressure and the displacement of the retaining structure. This paper aim at the problem that there is a high-rise building who has a CFG composite foundation next to the foundation pit, though cantilever retaining pile model test, simulate the excavate process, made a testing system to measure datum in order to research on the characteristics of the soil pressure, the moment on the retaining pile, the displacement of the pile wall, and the settlement of the CFG composite foundation. This paper mainly achievements are as follows:⑴During the excavate process of the foundation pit, the displacement of the pile wall is mainly upright.⑵When the depth of the foundation pit is less than the CFG composite foundation of it’s neighbor building, the pile wall is safer than have no neighbor building.⑶When the foundation pit is deeper than the CFG composite foundation of it s neighbor building, the pile wall is more dangerous than have no neighbor building.⑷During the excavate process of the foundation pit,the neighbor’s composite foundation could“adjust”the moment on the pile wall, from the top down, make it smaller and distribute more well-proportioned.⑸The“adjust”is a stress transfering process, the stress is transferred to the end of the pile wall.As the pit is deeper than it’s neighbour’s composite foundation, the stress is large enough to make the pile wall pierce into the soil under it.⑹The“soil column”is very important to keep the pit’s neighbour building fixing.更多还原