| The stability of surrounding rock in tunnels crossing faults has always been one of the most considerable topics in underground engineering.Along the Chuxiong section of the Central Yunnan Water Diversion Project,not only the red rocks in central Yunnan are widely distributed,but also the fault structure is developed.A total of 93 major faults above the Grade III structural plane were found.The scale of the faults varies,except for small and medium-sized faults of different widths.In addition,there are many regional faults.Compared with small and medium-sized faults,the stability of the surrounding rock of the tunnel encountered more severe challenges when the tunnel passed through these large faults because the width of the regional large-scale fault fracture zone was more than tens of meters.There are four regional large faults along the Chuxiong section of the Central Yunnan Water Diversion Project.The widths of the broken belts are all over 100 meters,and the extension length is tens of kilometers to hundreds of kilometers,which intersects the water transmission line at large angles.Based on this,the on-site investigation of the regional large-scale fault fracture zone traversed by the Chuxiong section of the Central Yunnan Water Diversion Project,and the Yuanmou-Luzhijiang fault zone as the research object.The comprehensive survey,the comparison and laboratory test research were conducted to obtain the physical and mechanical characteristics of rock and soil in the fault fracture zone.Combined with numerical simulation technology,the stability of the surrounding rock and the construction parameters optimization of the excavation footage of the Fenghuang Mountain Tunnel passing through the regional large fault in central Yunnan were studied and analyzed,the main research results of the paper are as follows:(1)Laboratory tests were carried out on the Yuanmou-Luzhijiang fracture zone and the Calcareous mudstone(K2j~3)on both sides of the faults to obtain their physical and mechanical indicators,combined with relevant specifications,rock mass integrity and engineering analogy analysis methods to comprehensively obtain Cretaceous soft rocks(K2j~3)and the numerical simulation parameters of the rock and soil in the fracture zone,which will lay the foundation for numerical simulation analysis.(2)Using numerical simulation and analysis software,a three-dimensional simplified model of tunnels crossing fault zones with different inclination angles is established,and the deformation law of tunnel surrounding rocks when tunnels crossing fault zones with different inclination angles are analyzed with and without advance reinforcement.It is concluded that the stability of the surrounding rock of the Fenghuang Mountain Tunnel is poor with the working condition of 75°angle,and the tunnel needs to be pre-reinforced when passing through the fracture and fracture zone.(3)Based on the simplified three-dimensional model,the deformation and stress of the surrounding rock and supporting structure of the tunnel under different excavation footages are compared and analyzed.According to the law,the reasonable excavation footage of the tunnel is 1m or 1.5m.In order to speed up the tunnel excavation speed,the excavation footage is recommended to be 1.5m.(4)Based on specific inclination angles and excavation footage,three-dimensional models of fault zones with different widths are established.The stability of the surrounding rock under the conditions of the Fenghuang Mountain Tunnel crossing the fault zone with different widths was simulated and analyzed.It is concluded that the range of stress and plastic zone produced by excavation increases slightly with the width of the fault zone.(5)Combining the numerical analysis results and relevant engineering experience,the construction principles and construction methods of the tunnel crossing the fault zone are summarized to provide reference suggestions for the relevant tunnel engineering construction. |
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