Study On The Influence Of Simultaneous Construction Of Shield Tunnel And Underground Excavation Station On Stratum Settlement And Station Structure

In the subway project in Beijing area,in order to reduce the impact of construction on the surrounding environment,the shield method is often used for the construction of section tunnels,and the underground excavation method is used for the main structure of the station.Under this kind of construction planning,it is generally necessary to provide the shield tunneling conditions after the bottom plate structure of the underground excavation station is completed.The Xiaoying West Road Station of Beijing Metro Line 27 is an additional station for planning adjustment,and the section tunnel is constructed by the shield method.The original design and construction process is: after the completion of the construction of the base plate structure of the station,the conditions for the shield tunnel to pass through the station are provided.Since Xiaoying West Road Station is an underground excavation subway station,there are many construction steps and a long overall construction period.It cannot provide the conditions for passing the station before the shield tunneling to the station,which affects the realization of the goal of "tunneling" across the line.In order to solve the contradiction between the construction period of the undercut station and the section shield tunnel,the construction method of the shield tunnel and the undercut subway station is proposed at the same time,that is,four small pilot holes on the upper floor of the station are constructed first,and then the shield tunnel passes through the station.,In the stage of shield tunnel passing through the station,the construction of the side piles in the pilot tunnel of the station and the steel pipe column in the middle of the station is interspersed.This paper adopts the method of "document research,theoretical analysis,numerical calculation and field monitoring" to study the superimposed effect of the simultaneous construction of shield tunnel and underground excavation station on the stratum settlement,the influence of shield tunnel excavation on the steel pipe column of the station and the reinforcement measures,The impact of shield tunneling on the upper guide tunnel of the underground excavation station and the reinforcement measures.The research contents and results are as follows:(1)A three-dimensional calculation model was established for two typical sections of the station(standard section and spatial intersection section),and the surface subsidence of different sections and the distribution law of surrounding rock plastic zone were analyzed.Reinforcement measures for embedded portal frame and reinforcement ring.Numerical calculation and field measurement results show that the reinforcement measures have a good control effect and ensure the safety of the station and surrounding environment.(2)Based on the Mindlin solution of elastic mechanics,the calculation formula of the additional stress generated by shield tunneling to the steel pipe column of the underground excavation station is deduced,and the rationality of the theoretical analysis is verified by numerical calculation method.In order to reduce the disturbance of the shield tunneling to the steel pipe column,two reinforcement measures are proposed: "setting a reinforcement ring at the junction of the steel pipe column and the primary support structure of the pilot tunnel" and "constructing the top longitudinal beam in advance".(3)A force sensor is arranged on the steel pipe column of the station to test the influence of shield tunneling on the steel pipe column.The results show that the influence of shield tunneling on the steel pipe column is more significant in the front and rear three rings,and the vertical stress variation range of the steel pipe column is maintained at-5.40MPa～8.61 MPa,the horizontal pressure change range is maintained within0～0.061 MPa.In general,the steel pipe column is less disturbed during the shield tunnel passing.(4)According to the characteristics of the shield tunnel adjacent to the upper pilot tunnel,the control measures for grouting reinforcement of the soil behind the initial support of the pilot tunnel arch and between the pilot tunnel and the shield tunnel are proposed.The variation laws of the indexes such as bottom plate settlement,clearance convergence and stress were studied,and the deformation of the initial support structure of the pilot tunnel was monitored on site.