Study Of The Impact Of Frozen Concealed Tunnel Underpasses On Upper Metro Stations

With the rapid development of urbanisation in China,more and more urban metro construction lines are being built,and the working conditions of new metros are becoming more and more complex,especially in the southeastern coastal region,where groundwater is extremely rich and uneven in this area,causing great disturbance to the construction of new metros,and even more demanding in terms of deformation control when encountering the situation of crossing existing metro stations.In this paper,a series of studies on the influence of frozen concealed tunnels on the upper existing metro stations when undercutting existing metro stations are done using a combination of numerical simulations,theoretical calculations and engineering field monitoring in the context of the study of the Fuzhou metro Line 4 undercutting Line 1 Chengmen Station in the southeast region.In the context of numerous related studies,various experts and scholars have repeatedly studied the influence of new tunnel undercutting construction on However,in the freeze-thaw environment,there is little research on the impact of concealed tunnels underneath existing metro stations during the positive freezing period,the tunnel concealment process and the soil thawing and sinking stage on the deformation of the upper existing metro stations at different times,based on which this topic is developed,the deformation laws and control strategies of existing metro stations at different times are studied.The specific research contents are as follows:(1)The pre-reinforcement scheme of the project is analysed and discussed,and the basic concept of using the artificial freezing method for soil pre-reinforcement is established to ensure that the project is safe in construction while taking into account the green environment.According to the relevant parameters of the project,a finite element numerical model was established to study the deformation of the upper existing metro station under different construction behaviours during the active freezing period,tunnel excavation period and thawing and thawing period,and the development of displacement of the upper existing station in each period and the distribution of displacement development path at the end of each period were obtained,and the deformation cloud map can more intuitively show the displacement changes in each period of the project construction.(2)Temperature and displacement measurement points were placed at designated locations on the project site and monitored throughout the construction phase to obtain temperature monitoring data during the active freezing period,maintenance freezing period and displacement monitoring data of the upper existing stations during the whole construction process.The numerical simulation results were also compared with the measured data,and the overall trend was found to be consistent,with the numerical simulation values being slightly overestimated.(3)The factors affecting the deformation of the upper existing stations in each period were analysed and deformation control methods were proposed.During the active freezing period of the frozen concealed tunnel,the deformation was controlled by reinforcing the soil with cement injection,and the simulation results showed that the soil layer reinforced with 10% cement could effectively control the deformation of the upper existing metro stations;whether pressure relief holes were set up or not also had a greater influence on the deformation of the freezing expansion.The analysis of the deformation factors and control measures of the upper existing metro stations during the tunnel excavation period and the thawing and sinking period will provide reference for similar projects.