Research On Influencing Factors And Control Technology Of Shield Underpassing Subway Line Deformation

When shield tunnel passes through the existing subway line,the construction will cause disturbance to the surrounding ground and cause ground deformation and settlement.The deformation is transmitted to the existing subway line by the soil between the new subway line and the existing line as the medium,which will cause settlement and deformation of the existing line.In order to ensure the safety of the existing tunnel,on the one hand,the deformation of the existing tunnel structure can be reduced by strengthening the ground,and on the other hand,the disturbance generated in the process of shield construction should be reduced.In this paper,by reading relevant materials at home and abroad,the research status of ground deformation caused by shield construction and its influence on surrounding structures are summarized.Through the understanding of the shield method construction process,based on Beijing metro line 17 workers sports yard under the ～ between xianghe garden station line in both the airport dongzhimen station ～ between sanyuanqiao station project cases,determine the construction process is likely to impact on settlement of existing structure factors(grouting pressure,earth pressure,the new line clear distance and Angle under wear,etc.).Based on the case data,a three-dimensional stratigraphic structure model was established to simulate the construction process of the case.The results of model analysis are basically consistent with the monitoring data of construction site,which confirms the feasibility of using finite element analysis software to conduct similar engineering simulation analysis.Through the analysis of the simulation data under different values of each influencing factor,it is found that in the construction process of similar projects,the appropriate pressure of the soil chamber is 1.1-1.4 times of the sum of the static earth pressure and water pressure in the center of the excavation face.The grouting pressure should be 1.4-1.8 times of the sum of the static earth pressure and water pressure at the grouting position.On this basis,the settlement deformation of the existing structure is small.Excessive pressure of the soil warehouse will cause excessive uplift of the existing structure,and excessive grouting pressure will increase the settlement value of the existing structure.In the design stage of the new tunnel line,attention should be paid to the underpassing Angle of the new line tunnel.When the Angle between the old and new lines is 90°,the influence on the existing line is the least,and the longitudinal settlement value of the existing line structure is also the least.At the same time,the appropriate adjustment of the net distance of the new tunnel is also helpful to the protection of the existing line structure.At present,when the net distance of the new tunnel in the crossing section is 2.13-2.14 times of the excavated face diameter of the new tunnel,the influence on the existing line structure is small.The degree of influence of the factors studied in this paper on the settlement deformation of the existing line structure is,in descending order,the net distance between the new line tunnel and >soil warehouse pressure > and the underpass Angle > grouting pressure.In response to actual engineering cases,in addition to measures such as structural reinforcement of existing lines,test sections should be set at similar positions of the stratum to check the correctness of parameters such as grouting pressure and soil warehouse pressure,so as to reduce the impact of construction on existing lines and ensure the safety of existing lines.