| In recent years,with the increasing scale and difficulty of foundation pit engineering,the safety accidents of tunnel structure and foundation pit caused by the Deep Foundation pit engineering adjacent to Subway Tunnel are not uncommon,the deformation characteristics of existing shield tunnel caused by the excavation of two-sided deep foundation pit are seldom studied,so the Metro Tunnel project adjacent to a two-sided deep foundation pit is taken as the research object in this paper,this paper first summarizes the general situation of the project,the geological and hydro geological conditions of the project and the bracing scheme of the foundation pit,then establishes the corresponding model using PLAXIS to carry on the parameter sensitivity analysis and selects the more suitable construction scheme to guide the construction,combined with the monitoring results,the deformation regularity of the adjacent metro tunnel during the construction of the double-side Deep Foundation Pit is analyzed and summarized.Finally,the internal force and deformation characteristics of the tunnel,diaphragm wall and other structures during the actual excavation are simulated by using the numerical model,the influence of horizontal distance,different construction sequence and thickness of support structure between outer wall of foundation pit and Subway Tunnel is analyzed.The results showed that:The construction time sequence of the excavation has different influence on the deformation of the existing tunnel and the supporting structure,especially on the horizontal displacement of the left arch waist and the horizontal deformation of the diaphragm wall near the side of the tunnel.Therefore,the construction scheme of double-side cross excavation is selected in the actual construction of foundation pit.The deformation of existing tunnel and supporting structure induced by excavation is closely related to the horizontal distance between them,and the horizontal distance has more significant influence on the vertical displacement of tunnel and the horizontal deformation of diaphragm wall adjacent to tunnel side.Considering the safety of the existing tunnel,the safety distance between the boundary line of the foundation pit and the subway tunnel is 10 m.The stiffness of support structure has an important influence on the deformation of existing tunnel and support structure.The internal force change and deformation trend of the bracing system indicate that the bracing structure plays an important role in the safe and orderly implementation of the whole project.During the excavation of foundation pit,the earth pressure is only related to the depth of diaphragm wall.The result of field measurement is close to the result of numerical simulation,and the error between the two is about 10%,which shows that the finite element model is reliable and desirable,the establishment of the model and the study of the sensitivity analysis of the parameters play an important role in the smooth implementation of the project. |
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