Research On Mechanical Characteristics Of TBM Construction Of Double-line Subway Tunnels In Composite Rock Formation

In order to improve the construction efficiency of metro tunnel and ensure the safety of construction,it is crucial to study the construction method of metro tunnel under complex interbed conditions,the ground surface settlement caused by TBM construction,and the real-time estimation of surrounding rock strength.Therefore,the Chongqing Metro Line 9 of the Zhongcong Tunnel was the research object of this study,and systematically analyzes the TBM equipment selection,adaptability analysis and targeted design under complex interbed conditions.By studying the application effect of compound TBM based on single shield in urban metro tunnel,the construction means and methods in the tunnel field are enriched.Based on the method of numerical simulation and field monitoring,investigate the behavior of ground surface settlement in TBM double-line tunnels constructed under existing buildings and to devise a calculative representation for that behavior.Based on the statistical analysis of the construction parameters of 17 rock tunnels including Zhongcong tunnel,a rock strength estimation formula adapted to both soft rock and hard rock is proposed,which solves the observation and evaluation of the excavated rock surface are difficult because of the TBM design defects.The main research contents and conclusions of this paper are as follows:(1)The compound TBM has absorbed the principle and advantages of the earth pressure balance shield,and the TBM equipment has been adaptability analysis and targeted design,which not only ensures the safety of construction,but also ensures the quality and efficiency of construction.It provides very valuable experience for the equipment selection of the metro tunnel construction project.(2)Using the numerical simulation orthogonal test,the influence of existing buildings on the settlement trough and the influence of TBM tunneling parameters on ground surface settlement were investigated.In addition,the formula for determining the ground surface settlement of double-line TBM tunnels was improved and applied to the Zhongcong Tunnel.The numerical simulation and calculation results were consistent with the actual measured results.(3)Based on the tunnel engineering practice and previous studies,a real-time method for estimating surrounding rock strength based on TBM tunneling parameters such as thrust,torque and cutting depth per revolution was proposed.The proposed method is robust to a wider range of cases and can be applied to both soft rock and hard rock tunnels.The construction parameters of 17 TBM rock tunnels are statistically analyzed,and a method is proposed for calculating two constants in the estimation formula.The proposed rock strength estimation formula is also applied to the Zhongcong Tunnel(soft rock)and Maiko Tunnel(hard rock),and the generalizability and reliability of the estimation formula are proved.