Study On Law Of Existing Tunnel Deformation Of Subway Station Crossing Engineering

With the construction of a large number of urban subway, a lot of construction projects and existing tunnel crossing phenomenon are inevitably encountered, worth still, more and more are developing towards the characteristics of "deep, large and near". So in the construction of the crossing project, effective measures are taken to reduce the deformation, which are necessary to ensure the operation with safety. In this paper, relying on a new station beneath the existing tunnel engineering, through methods of laboratory test, theoretical analysis, on-site data analysis and numerical simulation.etc, effects of deformation of the existing tunnel excavation of new foundation pit excavation are researched. The main research contents and results are as follow.Experimental study on the soil mass before and after grouting in the excavation face is conducted, which obtains shear strength, elastic modulus, cohesion and internal friction angle after.grouting. Soil cohesion is 2.1 times after grouting to before, which hs certain significance to engineering safetyConsidering formation pre grouting and group hole effect, the application of Peck formula in settlement calculation is deeply researched. On the basis of obtaining main parameters before and after the formation of the strata grouting, FLAC3 D is used for numerical simulation, proving direct superposition method of Peck formula is able to predict the existing settlement trend. Based on the relationship between the width of the settlement trough and the cohesion of soil mass, amendments of the application of Peck formula in pre grouting stratum, cohesion improvement coefficient 1 is raised. Compared to the original formula, the forecast result on the existing settlement, the difference of maximum settlement and numerical simulation results has decreased by 85.21%; on the basis of the modified of result, considering the release room of prior pilot tunnel excavation, deformation and release coefficient of group cavity effect is proposed, which further increases the accuracy of the prediction of existing settlement.Under the circumstances of one-way excavation, existing line floor settlement can be divided into initial settlement, rapid settlement and stabilization. Settlement amount caused by excavation stage 6 pilot takes 90% of total amount. Because prior pilot released room for later ones. The change of track settlement, track horizontal displacement and deformation seam opening degree conforms to similar law, representing the deformation caused by existing line base plate is the reason of other deformations.Numerical simulation studies show that in the period of initial support a jack is added on the basis of the pilot tunnel excavation, the existing floor settlement is reduced by 0.15mm~0.25 mm. Track settlement, differential settlement and horizontal displacement of rail track and track changes all decrease showing that exerting active support force can effectively decrease existing cable deformation.Based on the numerical simulation result of field measured data and one-way excavation without Jack, optimization scheme is proposed and numerical simulation study is carried out. Research results show that 0.11mm~0.3mm。The change of gauge, track differential settlement and deformation seam opening are all tiny. And the change curve of each monitoring project is gentle improving the existing stability in construction, which proves the practical value of the optimized scheme.