Study On The Stability Of The Shield Construction Crossing The Railway And Bridge In Sandy Pebble Stratum

In recent years,the development of urban underground space is in full swing,and the planning and construction of urban subway are also in progress.However,the special geological conditions and complex surrounding environment will increase the risk associated with shield construction,and some problems will become more and more significant.Based on the project background of Chengdu Metro Line 5,Saiyuntai Station to North Station West No.2 Road Station shield interval passing through the municipal bridge and the railway in operation,combined with theoretical analysis,numerical simulation,on-site monitoring and BIM technology,this paper made a more in-depth study on the shield tunneling construction technology passing through sandy pebble stratum.The main research work and achievements were as follows:(1)This paper analyzed the characteristics of sandy pebble stratum in detail,and put forward a reasonable and feasible shield selection scheme for sandy pebble stratum according to the characteristics of sandy pebble stratum.In addition,from the perspective of information management,the preliminary BIM technology implementation was carried out based on the background of the construction of shield crossing section.A BIM technology standardization evaluation system,which was suitable for the field of tunnel and underground engineering with maturity and standard degree as the core,was proposed for the first time.Based on this system,the implementation of BIM technology in shield crossing section was evaluated.(2)In this paper,the influence of shield tunneling on the municipal bridge and frame tunnel was studied,and a reasonable and feasible construction scheme was put forward.The research showed that the influence of 20# and 21# piers was more significant in the four areas of 19#,20#,21#,22#.It was suggested to strengthen the monitoring of the corresponding area in the construction process and take some reinforcement measures if necessary.Secondly,through the optimization of construction parameters and excavation scheme,the optimal grouting scheme and excavation scheme were determined.At last,the deformation control scheme of shield tunnel considering the influence of foundation pit excavation of frame tunnel was put forward,that was,the construction scheme of bolt at the bottom of tunnel.The feasibility of the scheme was also proved by the numerical simulation results.(3)In this paper,the influence of shield tunneling on the railway track was studied,and three schemes were put forward,such as double-layer pipe shed reinforcement,sleeve valve pipe tracking grouting and pedestrian channel steel reinforcement.At the same time,through comparative analysis,the deformation control effect of three schemes on the settlement of railway subgrade was demonstrated.The research results showed that for the deformation control of the railway subgrade,the double-layer pipe shed reinforcement scheme had the best effect,the sleeve valve pipe tracking grouting scheme was the second,and the pedestrian channel steel reinforcement scheme was relatively poor,but it played a certain role in controlling the stress of the pedestrian channel,and enhanced the integrity of the pedestrian channel structure to a certain extent.(4)According to the site construction situation,the corresponding monitoring plan was made,and the monitoring points were arranged on site to monitor the area affected by the shield tunneling construction.Then,the deformation law at the monitoring section and the monitoring points during the shield tunneling were analyzed in detail,and the field monitoring results were compared with the numerical simulation results.The analysis results showed that there was still a certain gap between the field monitoring data and the numerical simulation results,but on the whole,the numerical simulation results still had its significance and value for the study of deformation and stress change law and the feasibility demonstration of construction scheme.At present,the pace of urban underground space development in China is moving forward in an orderly manner,and similar problems may still be encountered in the followup subway construction.On the one hand,the research results of this paper provide guidance for the construction of the engineering,on the other hand,it aims to provide some reference for the follow-up similar projects and research.