【作者】 赵静；

【导师】 叶冠林； 秦承；

【作者基本信息】 上海交通大学 ， 建筑与土木工程（专业学位）， 2018， 硕士

【摘要】 深基坑开挖和支护是岩土工程领域目前研究的热点和难点,如何通过有效的支护手段控制基坑变形并确保基坑工程经济又安全,是岩土工程领域一个不断研究探索的一个课题。上海地区以软粘土地基为主,地基土的强度很低,地下水位很高,给深基坑支护设计及施工带来了较多的不利因素。临近正在运营地铁的基坑工程环境情况复杂,保护要求高,虽然近年来已有不少学者和技术人员针对此作了研究,但在临近地铁基坑的支护结构、土体位移及区间隧道的影响方面存在许多可研究的问题。本文依托临近地铁的上海地区某商办楼项目,利用有限元数值模拟,分析支护体系的变形及其对环境的影响,确立设计方案并根据环境保护要求优化支护体系结构。并将本文项目的施工情况及现场实测结果与分析结论进行对比分析,所得成果可供类似项目设计施工提供参考。本文就本项目的研究最终得到如下结论:(1)在有限元数值分析中,计算模型中各项参数的选用非常重要。尤其是在基坑工程的土体本构模型选取尤为重要,本次分析选用的土体本构模型为硬化土模型Hardening Soil模型,该模型能够模拟软土和硬土等多种类型土体力学特性。根据地质勘察报告所提供的参数及相关的试验结果提供的方法,取得合理的本构模型参数,在上海地区基坑工程进行有限元分析能够得到较为合理的结果。(2)通过有限元分析,可以得出本项目临近地铁侧基坑选用800厚地下连续墙进行支护,距离地铁隧道较近的二区基坑(距离约1倍基坑开挖深度)开挖对地铁区间隧道的附加变形为8.02mm,一区基坑(距离约2倍基坑开挖深度)开挖对区间隧道的附加变形为4.36mm。区间隧道的附加变形均在地铁保护控制要求范围内,基坑距离越远,对地铁的附加变形越小。(3)本研究通过调整临近地铁侧的支护刚度及坑内加固宽度来分析支护体系及区间隧道的变形。分别分析了三种支护刚度(800mm及1000厚地下连续墙、Φ900钻孔灌注桩)与三种坑内加固宽度(5m、8m、11m)的组合,发现了采用1000mm地下连续墙或者11m地基加固宽度,支护结构最大水平位移降低幅度过小,性价比较低;而采用Φ900钻孔灌注桩或者5m宽地基加固宽度,支护结构及其对环境影响偏大,不能满足临地铁侧保护要求。经分析后决定临近地铁侧采用800厚地下连续墙支护,加固宽度8m;地铁保护范围以外(一般为区间隧道外50m)的区域适当降低支护刚度,选用Φ900钻孔灌注桩,既确保基坑的安全同时又降低支护结构成本。(4)基坑施工过程中,严格控制支护结构及地基加固施工质量,在后期基坑开挖中进行全过程现场实测,并将实测变形数据与有限元计算结果进行对比分析。实测支护结构及土体水平位移、地面沉降变形曲线与计算结果基本吻合,如实测CX4的支护结构测斜曲线变形最大值为20.31mm,而模拟结果为18.64mm。验证了采用有限元进行基坑施工全过程分析,不仅仅能对支护体系及其对环境影响做出合理的预测分析;而且能体现在临近地铁侧基坑采用刚度较大的地下连续墙进行支护,坑内采用裙边加固,能有效的保护区间隧道的附加变形在地铁保护要求范围内。更多还原

【Abstract】 Deep excavation and supporting are the hot and difficult problems which are considered by geotechnical engineering.How to control deformation of foundation pit through effective supporting method and ensure the safety of the foundation pit are the constant topics in geotechnical engineering field.The soft clay foundation is widespread in Shanghai area.The strength of foundation soil is very low and the groundwater level is very high,which bring adverse factors to the design and construction of deep foundation pit.The environment of foundation pit engineering adjacent to subway is complex.Although many scholars have made a research on for this in recent years,but there are still many problems in the supporting structure adjacent to the subway foundation pit,displacement of soil,and influence of tunnel.Based on a commercial building project in Shanghai near the subway,this paper analyzes the deformation of the support system and its impact on the environment by using finite element numerical simulation,establishes the design scheme and optimizes the support system structure according to the requirement of environmental protection.In addition,the construction situation of the project in this paper and the field test results and analysis conclusions are compared and analyzed.The results can provide references for similar project design and construction.The conclusions of this study are as follows:(1)In the finite element numerical analysis,the selection of various parameters in the calculation model is very important.Especially in the foundation pit engineering of soil constitutive model selection is particularly important.In this study,the Hardening Soil model Hardening Soil model is used and it can simulate the soft soil and hard soil,and other types of Soil mechanics properties.According to the parameters provided by the geological survey report and the methods provided by the relevant test results,reasonable constitutive model parameters are obtained,and a more reasonable result can be obtained by finite element analysis of foundation pit engineering in Shanghai area.(2)Through finite element analysis,it is can be concluded that the project is near the subway side chooses 800 thick underground continuous wall for supporting foundation pit,metro tunnel deformation duo to excavation near the tunnel(the distance is about 1 times of foundation pit excavation depth)is 8.02 mm,metro tunnel deformation duo to excavation near the tunnel(the distance is about 2 times of foundation pit excavation depth)is 4.36 mm.The additional deformation of the interval tunnel is within the scope of subway protection control requirements.The farther the foundation pit distance is,the smaller the additional deformation of the subway is.(3)In this study,the deformation of the supporting system and interval tunnel was analyzed by adjusting the supporting stiffness and reinforcement width in the pit adjacent to the subway.Respectively analyzing the three kinds of supporting stiffness(800 mm thick and 1000 underground continuous wall,Φ 900 bored piles)and three kinds of pit reinforcement width(5 m,8 m,11 m)combinations,it can be found the underground continuous wall with 1000 mm or 11 m width of foundation reinforcement,maximum horizontal displacement of retaining structure to reduce the amplitude is too small and cost performance is low;While using Φ 900 bored piles or 5 m wide width of foundation reinforcement,supporting structure and its great impact on the environment,but it can not satisfy requirements over the side of the subway.Based on the above analysis,it is decided that 800 thick underground continuous wall is adopted to support the adjacent subway side and the reinforcement width is 8m.Outside the scope of protection of the subway(general for tunnel 50 m)area can decrease the supporting stiffness.Choosing Φ 900 bored piles can ensure the safety of the excavation and reduce the cost of supporting structure.(4)During the construction of foundation pit,the quality of supporting structure and foundation reinforcement construction shall be strictly controlled.The whole process of field measurement should be carried out in the later excavation of foundation pit,and the measured deformation data should be compared and analyzed with the finite element calculation results.The curves of the measured support structure,soil horizontal displacement and ground settlement deformation are basically consistent with the calculated results.For example,the maximum value of the measured slope curve of the support structure CX4 is 20.31 mm,while the simulated results are 18.64 mm.It is proved that the whole process of foundation pit construction is analyzed by finite element method.In addition,it can be seen that the foundation pit of the adjacent subway side is supported by the underground continuous wall with large rigidity and the apron edge is used to reinforce the pit can effectively protect the additional deformation of the tunnel.更多还原