【作者】 李琳；

【导师】 杨敏；

【作者基本信息】 同济大学 ， 岩土工程， 2007， 博士

【摘要】 在高水位或软弱土层含水丰富地区进行深基坑的开挖必须进行工程降水，工程降水为基坑开挖提供干燥施工环境，对加固土体和稳定边坡、减小地下水的危害也有很重要的作用。但是工程降水会使基坑周围渗流场变得复杂，如果不能正确分析，势必会引起误差甚至错误，同时对水土压力分布及基坑性状产生影响，还会引起坑外地下水位的降低导致地面沉降影响环境等，所以正确分析和估算工程降水对基坑及周边环境的影响是很重要的，本文主要进行的研究工作如下：1．以大量工程实测数据同时结合有限元计算，分析了软土地区深基坑的变形特性，包括基坑围护结构侧移、坑底隆起变形和周围地层沉降的性状及其影响因素，并建立了基坑工程的变形控制标准。2．分析了工程降水对深基坑土体的预压加固作用，基坑渗流稳定破坏原因和基坑渗流网特点，工程降水对围护结构水土压力的影响，分析了承压水作用下考虑土体强度的圆形基坑底板临界厚度计算，并提出可供实际应用的简化计算公式。3．分析了基坑降水引起的不同含水层土层中应力变化和疏干区的土体的持水密度，应用FLAC程序分析了工程降水引起基坑周围地面沉降的规律，包括弹性模量、降水深度、渗透系数对地面沉降的影响。分析了工程降水引起的基坑周围地面沉降的分布特点和规律，并提出一种由工程降水引起的坑后地面沉降简化计算方法。4．对上海世博地下变电站基坑工程进行同时考虑土体与结构共同作用和流固耦合的数值模拟分析，就仅考虑开挖与同时考虑开挖和工程降水，对比分析了该基坑的变形及周边地面沉降隋况。结果表明，虽然由于软土的低渗透性而导致差别很小，但是工程降水会引起基坑变形增大，如果不考虑工程降水影响是偏于不安全的。本文着重分析了工程降水对深基坑性状及周边地面沉降的影响，希望能为深基坑的设计施工尽一点微薄的力量。更多还原

【Abstract】 Dewatering is necessary in the excavation under the ground water level in softclay, which provide a dry enviroment for the excavation and is benefit for the slopestability and reducing the harm induced by the groundwater. But dewatering canmake the seepage field more complex around the excavation,error may come intobeing if the seepage field can not be analyzed correctly.Dewatering have importanteffect on the behaviour of the foundation pit and the surrounding soils, seepageinduced by dewatering from outside to the inside of the foundation pit have effect onthe stability and the deformation of the foundation pit and surface settlement for thevertical consolidation by the underground-water drawdown out of the foundationpit. So it is very important to analyse and estimate the dewatering effect on the deepexcavation and surroundings.The primary research work of this paper is as follows:1. Based on the 46 case histories and result of the finite element methodcalculation, the deformation characteristic of the deep excavation engineering in softclay is analyzed,which include the characteristic of the maximum lateral deflectionand basal heave and surface settlement.The deformation control criterion is alsostudied.2. The effect of preconsolidation pressure by dewatering on the soil in thefoundation pit is analyzed, the harm of the seepage to the stability and the seepagefield′s characterize is analyzed also,The earth pressure due to dewatering isinvestigated.The formula of the critical thickness of the soil layer withstandingpressure water in the columniform foundation pit is also derived.3. The density of soil and stress increment induced by dewatering around thefoundation pit is investigated,the behaviors of settlement induced by dewatering wereanalyzed by FLAC program and three main effective factors such as Young’smodulus, dewatering depth and permeability were taken into account. A simplifiedmethod for calculating settlement by the dewatering is derived, the characteristicsand the rule of settlement induced by the dewatering is also analyzed. 4. Numerical analysis of considering consolidation and interaction between theexcavation support and the soil by using FLAC3D software in the super deepexcavation of the underground transformer substation for the world exposition ofshanghai 2010. The results not considering dewatering are compared with the resultconsidering dewatering, including wall deflections, basal heave, surfacesettlement, The analysis of considering leakage of the wall and leakage betweenconfined aquifer is provided also. The analysis shows that although the difference issmall in soft clay due to the low permeability of the soil, dewatering enhance thedeformation of the foundation pit and the foundation pit is inclined to be not securityif dewatering is not considered, the effect of leakage of the wall can be obvious onthe surface settlement.In the end, this paper study the dewatering effect on deep excavation andsurrounding, especially the surface settlement induced by excavation and dewateringand provide some reasonable and efficient support for the design and construction ofthe foundation pit.更多还原