紧邻既有建筑基坑支护中几个问题的研究

发布时间：2018-04-05 22:01

本文选题：地表超载　切入点：有限土体　出处：《清华大学》2013年硕士论文

【摘要】：紧邻既有建筑的基坑开挖过程中对变形控制非常严格，同时坑周土体宽度有限使得很多支护方案在这里都不适用，因此对这类基坑支护进行研究具有重要意义。本文在前人已有研究成果基础之上，通过理论分析与数值模拟相结合的研究方法，针对这一类基坑支护设计时遇到的几个问题进行了系统的研究。论文前半部主要研究各种不同情况下的土压力计算方法，随后在此基础上对紧邻既有建筑基坑的支护设计进行了探讨。具体的研究工作包括以下几个方面：（1）通过理论分析和数值模拟对现行规范中有关坑边局部荷载引起支护结构上土压力的规定进行了较深入的讨论，分析了土体参数c和φ对附加土压力弹塑性解的影响，发现其与静止土压力系数的正比例关系；针对土体分层情况，利用有限元法分析了附加土压力的分布形式；针对基坑周边建筑物荷载的作用，分析了基础埋深对附加土压力的影响。利用正态分布曲线拟合了下卧土层的附加压力，并在此基础上推出了计算地表超载引起挡土结构上附加土压力的简化公式。（2）基坑挡土结构与既有建筑基础间形成有限土体，此时土压力的计算不能采用通常情况下的朗肯理论或库伦理论。通过对挡土墙与既有建筑基础间的有限土体进行完整的受力分析，考虑了既有建筑基础与有限土体间的法向及切向相互作用力，建立了求解有限土体主动土压力的计算公式，并进行了适当的简化。通过与有限元结果对比证实本文给出的简化公式形式较为简捷，精度较高。在应用公式的过程中要考虑位移的因素以及中主应力对强度参数的影响，本章对这些问题也进行了讨论。（3）分析了水对土压力的影响，包括渗流对土压力的影响，以及非饱和土与饱和土强度差异引起土压力的不同。（4）由于锚杆的设置受到限制，常使护坡结构的横向支护不足，寻找其他措施以减小变形成为这类基坑支护需关注的重点。通过三维数值模拟各种不同的支护方案，，发现了一些减小变形的方法：上部土钉墙支护并适当放坡可有效减小护坡桩的悬臂长度；双排桩对这类基坑支护有一定的优势；充分利用周边建筑原来的支护系统等等。对桩径的选取、放坡的深度也进行了讨论。提出一种新型的支护方案，通过限制桩顶弯曲达到减小变形的目的，经有限元验证其效果不错。
[Abstract]:The deformation control is very strict in the excavation of the foundation pit adjacent to the existing building, and the limited width of the soil around the pit makes many supporting schemes not applicable here, so it is of great significance to study this kind of foundation pit support.In this paper, based on the previous research results, through the combination of theoretical analysis and numerical simulation, several problems encountered in the design of this kind of foundation pit support are systematically studied.The first half of the paper mainly studies the calculation methods of earth pressure under different conditions, and then discusses the supporting design of the foundation pit adjacent to the existing building.Specific research efforts include the following:1) through theoretical analysis and numerical simulation, the regulations of soil pressure on supporting structure caused by local load on pit edge in current code are discussed in depth, and the influence of soil parameters c and 蠁 on the elastoplastic solution of additional earth pressure is analyzed.It is found that it is proportional to the coefficient of static earth pressure, the distribution form of additional earth pressure is analyzed by finite element method in the case of soil stratification, and the effect of building load around foundation pit is analyzed.The influence of the foundation depth on the additional earth pressure is analyzed.The additional pressure of the underlying soil is fitted by the normal distribution curve, and a simplified formula for calculating the additional earth pressure on the retaining structure caused by the surface overload is derived.2) a finite soil mass is formed between the retaining structure of foundation pit and the foundation of existing buildings, and the calculation of earth pressure can not be done by Rankine's theory or Coulomb's theory.Through the complete force analysis of the limited soil mass between the retaining wall and the existing building foundation, considering the normal and tangential interaction between the existing building foundation and the limited soil mass, a formula for calculating the active earth pressure of the finite soil is established.A proper simplification is carried out.By comparing with the finite element results, it is proved that the simplified formula given in this paper is simple and accurate.The factors of displacement and the effect of intermediate principal stress on strength parameters should be considered in the application of the formula. These problems are also discussed in this chapter.3) the influence of water on soil pressure, including the influence of seepage on soil pressure, and the difference of soil pressure caused by the strength difference between unsaturated soil and saturated soil are analyzed.(4) due to the limitation of bolt setting, the transverse support of slope protection structure is often insufficient, so finding other measures to reduce deformation has become the focus of attention for this kind of foundation pit support.Through three dimensional numerical simulation of various support schemes, some methods to reduce deformation are found: the upper soil nailing wall support and proper slope placement can effectively reduce the cantilever length of slope protection piles, and double row piles have certain advantages to this kind of foundation pit support.Make full use of the original supporting system of surrounding buildings and so on.The selection of pile diameter and the depth of slope are also discussed.A new support scheme is proposed, which can reduce the deformation by limiting the bending of the pile top.
【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU753

【参考文献】