Deformation Monitoring And Analysis Of Deep Foundation Pit Excavation In Wuxi Metro Line Two

With the rapid development of urban construction,road traffic has been unable to meet people's travel needs.As an efficient,environmentally friendly and cheap transportation tool,subway has become a typical case of underground space development and utilization.Thereare many features of foundation pit engineering,such as strong risk,regionality,comprehensiveness,time and space effect and time effect.How to control the deformation of foundation pit in a reasonable range is a topic which we have been exploring.During excavation,foundation pit disturbs the surrounding soil and changes the stress and strain state of the soil.It is in an unstable state,and the force balance of original soil would be damaged.In the process of excavation,soil collapse,loss,uplift and settlement will occur.Especially in constructing subway of urban area,we must pay attention to the influence of surrounding buildings and underground pipelines in the limited range of foundation pit excavation,and consider many factors.The concrete effects of foundation pit excavation are as follows: firstly,it causes the horizontal or vertical displacement of the soil;secondly,it is the uneven settlement of the ground;and thirdly is the settlement of the building.In this paper,the development status of foundation pit engineering is introduced,and the monitoring contents and monitoring methods of subway tunnel,the causes and influencing factors of tunnel deformation are explained.The contents and methods of deformation monitoring for deep foundation pit of subway are introduced.The supporting axial force and control of underground water and deformation mechanism of foundation pit in subway construction are introduced.Based on the monitoring results of Wuxi metro line two Dawangji station to Heliekou station,it had been analyzed the monitoring data of continuous wall top horizontal displacement,vertical displacement,surface settlement,deep horizontal displacement,subsidence,and groundwater in the process of excavation.The monitoring data should be analyzed timely,Meanwhile,when it exceedsprewarning value it ought to reportimmediately,and find out the change rules among different excavation time periods,different excavation depths and different monitoring items,and optimize the design plan,and control the deformation and settlement within the permitted scope.(1)After excavation,the depth of excavation is larger than before,and the horizontal displacement of the top surface of the continuous wall is the largest.When the foundation is built,the displacement of the top of the wall will tend to be stable.(2)The vertical displacement of the continuous wall increases with the increase of the excavation depth.The displacement is the largest in the pit depth 1/3,and the supporting work should be done in time.(3)Through the monitoring of the supporting axis force,the pressure of the soil on the continuous wall can be obviously felt.When the first support is erected,the axial force is rapidly increasing.After the second support is set up,the first support force decreases obviously.After the erection of the third support,the second support forces descend obviously,in order to ensure the stability of the foundation pit and excavation in the excavation.The next support should be set up in time.(4)through the analysis of the surface subsidence,the disturbance of the surrounding soil is far away from the foundation pit,which is close to the foundation pit,and the settlement is obvious,and the settlement is small.(5)comparing the horizontal displacement and vertical displacement of the deep soil,it is found that the deformation law is similar.