【作者】 王鹏飞；

【导师】 童小东； 雷秋生；

【作者基本信息】 东南大学 ， 土木水利（专业学位）， 2023， 硕士

【摘要】 本文依托苏州华贸中心深基坑项目,采用现场监测、理论计算和数值模拟等手段,对苏州软土地区邻近地铁车站深大基坑工程支护设计开展研究,基于对基坑自身及周边环境变形影响因素的分析,提出了相应的支护设计方案。将数值模拟结果与监测数据等进行了对比,并提出了进一步优化建议。本文的主要工作如下:(1)通过总结深基坑支护设计理论,初选了两种基坑支护形式:地下连续墙+内支撑;咬合桩+内支撑。采用模糊综合评判决策与层次分析法相结合的方法选出了“地下连续墙+内支撑”这一较优的支护形式。对设计院提出支护设计方案的主要剖面采用理正深基坑支护结构设计软件进行了计算。(2)对设计院提出的支护设计方案采用Midas/GTS软件开展了数值模拟,并与基坑监测数据进行了对比,结果表明:随着基坑开挖深度的增大,地下连续墙沿深度方向的水平位移先增大后减小,墙体沿深度方向的变形曲线呈“弓”形;基坑周边地表沉降随着距坑边距离的增加先增大后减小,最大地表沉降出现在距坑边8m左右的位置;基坑中心线附近坑底隆起值大,随着距中心线距离的增大,坑底隆起值逐渐减小;地铁车站北段位移大、南段位移小,车站在水平方向上发生了向基坑一侧的位移;同时,车站发生了较明显的沉降,且不均匀沉降现象明显。(3)通过数值模拟对影响本基坑变形的主要因素进行了分析,得出以下结论:地下连续墙嵌入比的增大可以较好地限制支护结构水平位移以及基坑周边地表沉降,在一定范围内也可使基坑坑底隆起减小;“两道钢筋混凝土支撑+两道钢支撑”的水平支撑方案可以使支护结构和地铁车站的水平位移以及支撑轴力较明显地减小;钢支撑预加轴力值的增大可以很好地限制支护结构水平位移和基坑周边地表沉降,预加轴力值的增大会使钢支撑上的初始轴力增大,基坑开挖过程中的支撑轴力增量减小;槽壁加固深度的增大可以限制加固体范围内的支护结构水平位移、基坑坑底隆起、基坑周边地表沉降以及地铁车站的位移。(4)基于影响本基坑变形的主要因素分析,提出了对支护设计方案的优化建议:近地铁车站侧地下连续墙嵌入比调整为1.0,其他区域地下连续墙嵌入比调整为0.9;A1、A4、C2这三个基坑分区的水平支撑方案均调整为“第一、二道为钢筋混凝土支撑,第三、四道为钢支撑”;基坑中的钢支撑均预加轴力,预加轴力值调整为支撑轴力设计值的70%。(5)对优化后的支护设计方案开展了数值模拟,结果表明:采用优化后的支护设计方案,基坑和邻近地铁车站的各项位移明显减小。对于苏州软土地区邻近地铁车站深大基坑,建议对基坑进行分区支护设计,在邻近地铁车站一侧设置长条形的基坑分区;基坑竖向支护结构一定要嵌入足够深度;在设置水平支撑时宜将钢筋混凝土支撑和钢支撑以合理比例组合起来;钢支撑中一定要预加足够大小的轴力;在确定槽壁加固深度时应确保加固体底端位于(弱)承压含水层以下。更多还原

【Abstract】 Based on the deep foundation pit project of "Huamao Center" in Suzhou,this paper adopts on-site monitoring,theoretical calculation and numerical simulation to study the support design of deep foundation pit engineering near metro stations in Suzhou soft soil area.Based on the analysis of the factors affecting the deformation and stability of the foundation pit itself and its surrounding enviroument,the corresponding support design scheme is proposed.The numerical simulation results are compared with the monitoring data,and some suggestions for further optimization are put forward.The main work of this paper is as follows:(1)By summarizing the deep foundation pit support design theory,two types of foundation pit support are selected:underground continuous wall+internal support;Occluding pile + internal support.The optimal support form of "underground diaphragm wall + internal support" is selected by the method of fuzzy comprehensive evaluation and decision making combined with hierarchical analysis.The main section of the support design scheme proposed by the design institute is calculated by using Lizheng deep foundation pit support structure design software.(2)Midas/GTS software was used to carry out numerical simulation of the support design scheme proposed by the design institute,and the comparison was made with the monitoring data of foundation pit.The results showed that:with the increase of the excavation depth,the horizontal displacement of the underground diaphragm wall along the depth direction first increased and then decreased,and the deformation curve along the depth direction of the wall showed a "bow" shape;With the increase of the distance from the pit edge,the surface settlement around the foundation pit first increases and then decreases,and the maximum surface settlement occurs at about 8m away from the pit edge.The uplift value of pit bottom near the center line of foundation pit is large,and the uplift value of pit bottom decreases with the increase of the distance from the center line.The displacement in the north section of the subway station is large,the displacement in the south section is small,and the displacement in the horizontal direction is toward the foundation pit side.At the same time,the station has obvious settlement,and the phenomenon of uneven settlement is obvious.(3)The main factors affecting the deformation of the foundation pit are analyzed through numerical simulation,and the following conclusions are drawn:the increase of the embedment ratio of the underground diaphragm wall can better limit the horizontal displacement of the supporting structure and the ground settlement around the foundation pit,and can also reduce the uplift of the foundation pit bottom within a certain range;The horizontal support scheme of "two reinforced concrete supports+two steel supports" can significantly reduce the horizontal displacement and supporting axial force of the supporting structure and subway station.The increase of the preloading axial force value can limit the horizontal displacement of the supporting structure and the grounnd settlement around the foundation pit well.The increase of the preloading axial force value will increase the initial axial force on the steel support,and reduce the increment of the supporting axial force during the foundation pit excavation.The increase of reinforcement depth can limit the horizontal displacement of support structure,uplift of foundation pit bottom,surface settlement around foundation pit and displacement of subway station.(4)Based on the analysis of the main factors affecting the deformation of the foundation pit,the optimization suggestions for the support design scheme are put forward:the embedment ratio of the underground diaphragm wall near the subway station is adjusted to 1.0,and the embedment ratio of the underground diaphragm wall in other areas is adjusted to 0.9;The horizontal support schemes of A1 A4 and C2 are adjusted to "the first and second roads are reinforced concrete supports,and the third and fourth roads are steel supports".The steel supports in the foundation pit are preloaded with axial force,and the preloaded axial force value is adjusted to 70%of the design value of the supporting axial force.(5)The numerical simulation of the optimized support design scheme is carried out,and the results show that the displacements of the foundation pit and adjacent subway stations are obviously reduced by adopting the optimized support design scheme.For deep and large foundation pits near subway stations in soft soil area of Suzhou,it is suggested to cany out partition support design of foundation pits,and set up long partition of foundation pits near subway stations.The vertical support structure of foundation pit must be embedded in sufficient depth;When the horizontal support is set,the reinforced concrete support and steel support are combined in a reasonable proportion;Sufficient axial force must be added to the steel support;When determining the reinforcement depth of the tank wall,ensure that the bottom end of the added solid is below the(weak)confined aquifer.更多还原