| Long tunnels are generally seen as control project of traffic facilities construction because of its large depth,long extension and complicated engineering geology.Many hard rock tunnels pass through high geo-stress zone with the increase of depth,under this circumstance,the problem of rock burst can not be ignored.Rock burst is one of the most unstable phenomena in the field of underground engineering,it may threat the security of construction workers and equipment with the sudden release of energy.This problem has become one of the most difficult problems in the field of underground engineering.Based on Micangshan Tunnel of Bashan Highway,this paper studied disaster-causing mechanism,control and forecasting technology of deep-buried hard rock tunnel.This paper also combines engineering practice to optimize the construction scheme of rock burst sections of Micangshan tunnel from the angle of active and rapid protection,which greatly improves the construction efficiency and safety.This study can provide reference for similar projects in China.The main research results are as follows.(1)Basic mechanical parameters and initial stress characteristics of the surrounding rock in high geo-stress hard rock sections of Micangshan tunnel are obtained by the way of indoor and field tests.On the basis of this,the characteristics of the excavation of high geo-stress hard rock tunnels are studied.(2)Mechanical characteristics of rock deformation and failure are studied by the way of investigation and theoretical analysis,and transformation confining pressure between different rock failure types is obtained.On this basis,the relationships between the adjustment of the stress state of surrounding rock and the failure types of surrounding rock is established,the stress state and energy accumulation and dissipation characteristics of the surrounding rock are analyzed.(3)This paper used FLAC3D numerical simulation software to simulate the excavation process,obtained spatial and temporal evolution rules of stress and displacement caused by excavation.Combined with single hole acoustic wave test and UDEC discrete element software,the excavation damage range of deep buried section of Micangshan tunnel is studied.The results can provide basis for the selection of supporting means and parameters.(4)This paper puts forward the construction method of flexible protective net which is used in rock burst section.In this method flexible protective net support is introduced to cooperate with shotcrete bolt support,so they can complement each other's advantages and effectively protect against different grades of rock burst disaster.This paper compared flexible network support system with traditional support method in respects of construction efficiency,supporting effect and safety and studied its economic benefits and application prospects.(5)On the basis of the research on the stability of tunnel excavation and the excavation damage,this paper made a study on the parameter optimization of the flexible protective net system of high geo-stress hard rock tunnel and obtained mechanical behavior and deformation characteristics of flexible protective net system. |
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