Analysis Of Influencing Factors On Surface Settlement Of Metro Station Foundation Pit Construction

Study on engineering subsidence of foundation pit is a problem can not be ignored,the influence of many factors and complex,this is a great challenge to the current engineering construction.At present,the design,construction,geological and hydrological conditions are the main factors affecting the foundation pit deformation,these can not be ignored.This article we use Hefei Mingguang Road station foundation pit engineering as the background,through the use of MIDAS / GTS to station foundation pit modeling and on ground settlement under different factors to study the impact,mainly on different support quantity of the excavation,excavation width,L/H and buried depth of retaining structure under the surface sink down to study,work and achievements are as follows:(1)First of all,this article on the domestic and foreign development foundation pit excavation surface subsidence development status and finite element software development of the article,a detailed description of the at this stage of subway station the main excavation methods,detailed description of the problems existed in land subsidence simulation study.(2)Secondly,in the second chapter of foundation pit excavation deformation mechanism a analyzed,including the enclosure structure deformation,ground surface settlement behind the wall,heave;and introduces the excavation surface subsidence form and common ground settlement calculation method,finally,according to the different factors on settlement influence analysis,which mainly includes design and construction factors.(3)In the third chapter we establish Mingguang Road subway station excavation model.The idea is first,elaborates on the use of MIDAS / GTS and finite element calculation method,and the constitutive model selection,introduce general situation of Mingguang Road Foundation,establish the corresponding boundary conditions and parameters,in Mingguang Road Station surface subsidence monitoring data simulation,compared the actual monitoring of surface subsidence rules with two-dimensional modeling of surface subsidence rule and along with the process of foundation pit excavation,ground settlement gradually,the maximum ground surface settlement are in the vicinity of the 11.3mm,so the model established,selection of parameters,the constitutive model,boundary loads applied are reasonable.(4)In the fourth chapter,we discuss the different factors under the influence law of ground surface settlement and select the DB9 section from the different support quantity,excavation width,L/H ratios and buried depth using MIDAS/GTS simulation.The influence of different factors on the surface subsidence is as follows:(1)Firstly,the number of support surface subsidence,the number was four in selected support,five support,six support of surface subsidence rule,finally a support is set in18.2m,at this time,four support a total of 7 cases,five support a total of 8 cases,a total of six support 9 conditions,intermediate support space erection,respectively to the last condition of surface subsidence were studied,with the support of the increase in the number of Mingguang Road Surface Subsidence pit simulation becomes smaller,the four support case,the maximum ground surface settlement of foundation pit is far greater than the five support and the six support for 12.58 mm.And the maximum settlement occurred in near the edge of the pit 10 m,but also can be found in the supporting amount to 5 support,the largest settlement value basically in the vicinity of 11 mm,the surface subsidence curve Like,and then continue to increase support,control surface settlement effect is not obvious,and in a certain range and support can well control the deformation,but support the use of a number of have a certain limit,it is waste of cost and have the construction excavation effect,time delay,resulting in temporal and spatial effect of foundation pit deformation is too large,so in the foundation pit design must combine with the actual situation of the project to set up a number of support。(2)Different excavation width influence.By the simulation deformation comparison chart shows,the excavation process,with the excavation width from the 21m-23.2m-25 m.At this time,the ground surface settlement significantly increased,and increased amount obviously,the maximum subsidence occurs in the excavation width 25 meters,14.86 mm and predictably in excavation of foundation pit of the width of the on surface subsidence influence,possibly because the excavation width increases,due to the presence of underground continuous wall on both sides of the pit,the width changes will the underground continuous wall limiting effect on ground surface settlement is more and more small,we can draw a conclusion that the excavation width is affecting the surface settlement of a main factor.(3)Study on the L/H ratio on the surface subsidence,respectively from 0.5,1,2,4,6,8,10,Through 8 stage simulation study,it is concluded that the maximum surface settlement of foundation pit is maximum when the ratio of excavation width to depth is 0.5.The general performance of the overall settlement of foundation pit,and the pit edge with the distance more and more far,the settlement value is more and more small,probably because of the small width ratio by retaining structure constraint large excavation,deformation is not obvious,when L/H becomes larger,the supporting structure of the constraints will be relatively smaller.The surface settlement becomes larger,but by comparison,when L/H is more than 8,the settlement reached a peak,24.26mm,at this time to further increase the ratio of surface subsidence and will further increase,but also can be found in the edge of the pit uplift value with the variation of L/H,its variation is very complicated,when the L/H is 4 the maximum is 10.34mm,the vertical surface subsidence area should be equal to the area and the heave of foundation pit retaining structure and the lateral deformation(without considering the effect of consolidation of soil and groundwater).(4)Analysis of the depth of retaining wall on ground settlement,selection of wall depth is 0.5H,0.9H,1.2H in the condition of 8 different depths of surface subsidence is studied,when the embedded depth of the wall is larger than 0.5H,with the increase of buried depth,surface subsidence is reduced,while the L is greater than 0.9 times of the excavation depth of H,the retaining structure stiffness increases not obviously lead to surface settlement did not change significantly,control deformation ability will therefore become large,long-term station excavation engineering experience shows that the wall thickness is 0.05 times of the excavation depth,and the depth of about 0.55 H to 0.8H,in this range,a reasonable increase of buried depth can effectively control the deformation of foundation pit depth,Hefei Mingguang Road subway station foundation pit retaining structure in 0.55 H to 0.8H is also considered to design.