Research On Excavation Method For High Side Wall And Super Large Section Subway Stations In Soft Rock Strata

In recent years,the construction of high embankment super-large cross-section tunnels in soft rock formations has become increasingly common.Unlike other ordinary tunnels,the mechanical properties of high embankment super-large cross-section tunnels are more complex,and the construction difficulty is greater.Therefore,the research on excavation methods for high embankment super-large cross-section metro stations in soft rock formations is of great significance.Taking Yudaishan Metro Station,the third station of the western extension of Chongqing Rail Transit Line 4,as the background,this article investigates and theoretically analyzes commonly used excavation methods for super-large cross-section tunnels.Using a combination of similarity model experiments and numerical simulation,the displacement,stress,and initial support force of surrounding rocks under different working conditions were analyzed.In addition,based on the aforementioned conclusions,the excavation length,thickness of sprayed concrete,and width of the intermediate rock column were optimized using orthogonal experiments.Through data comparison analysis,the optimized method has a smaller disturbance to the surrounding rocks.The main research results are as follows:(1)A survey was conducted on the commonly used excavation methods for large cross-section tunnels,and theoretical analysis and preliminary selection of the excavation methods commonly used in soft rock formations and high retaining walls were carried out.(2)The elastic modulus and cohesion of surrounding rock materials were determined by direct shear test and unconfined compression strength test under different mixing ratios,which provided data support for subsequent model experiments.(3)Based on the principle of similarity and the actual situation of Yudai Mountain metro station,a tunnel model experiment was established using barite powder,quartz sand,gypsum,and rosin-alcohol solution as materials.The excavation simulation of three excavation methods,namely,the intermediate rock pillar method,the traditional double-side wall pilot tunnel method,and the arch cover method,was completed.The displacement,stress,and initial support force of the surrounding rock were comprehensively analyzed under the three working conditions.It was initially suggested that the Yudai Mountain metro station should prioritize the intermediate rock pillar method and the traditional double-side wall pilot tunnel method.(4)On the basis of similar model experiments and numerical simulations,a detailed study was conducted using orthogonal experiments to investigate the significant effects of construction parameters such as excavation footage,shotcrete thickness,and middle rock column width on surface settlement,arch settlement,bottom heave,and lateral convergence of the reserved middle rock column method.