Study On Mechanical Characteristics And Disaster Prediction Of Deep Buried Section Of Metamorphic Sandstone Tunnel

High ground stress is one of the main harsh environments faced by mountain tunnel construction.In the 14 th five year plan,Our country requires to further accelerate the interconnection of national transportation infrastructure,and the construction scale of mountain tunnels will continue to expand in the future.Therefore,it is very necessary to study the mechanical properties and disaster prediction of surrounding rock under the condition of high ground stress in the deep buried section of mountain tunnel.The research content mainly includes two points in my paper:Firstly,the mechanical properties of metamorphic sandstone in uniaxial graded cyclic loading and unloading test are studied by using material servo machine,acoustic emission monitoring system and ultrasonic monitor.Secondly,the earthquake disaster,rock burst disaster and large deformation disaster of surrounding rock in the deep buried section of a metamorphic sandstone tunnel in Huangshan area are predicted and discriminated by using the methods of theoretical analysis and numerical simulation.The main conclusions are as follows:(1)Based on the systematic uniaxial graded cyclic loading and unloading test of metamorphic sandstone,the acoustic emission and wave velocity characteristics of metamorphic sandstone are studied.It is found that on the eve of loading failure,the acoustic emission activity of metamorphic sandstone will have a process of sudden rise and then sudden drop.After the sudden drop,the rock will be damaged in a short time,and the acoustic emission signal reaches a significant peak during failure.That is,the acoustic emission activity of metamorphic sandstone has the phenomenon of "quiet period".There is a stress "threshold" in the variation of wave velocity of metamorphic sandstone.When the stress exceeds this "threshold",the degree of rock damage will increase significantly and the wave velocity of rock samples will decrease rapidly.In engineering,the "quiet period" of acoustic emission of metamorphic sandstone and the rapid decline of wave velocity of rock mass can be used to predict the failure and instability of rock mass.(2)By analyzing the field drilling survey data,it is determined that the deep buried section of the tunnel has the characteristics of high ground stress field,and the in-situ stress state of the cross section of the tunnel is calculated.(3)The rock burst disaster of the surrounding rock of the deep buried section of the metamorphic sandstone tunnel is predicted by comprehensively using various theoretical criteria such as the analysis method of macro geological characteristics and the strength stress ratio method of surrounding rock.It is pointed out that there will be no rock burst in the surrounding rock of the deep buried section of the tunnel,which is enough to affect the construction safety.(4)The numerical simulation of the deformation characteristics of the surrounding rock and the initial support combination after the pre reinforcement of the deep buried section of the tunnel is carried out.The numerical simulation results and the actual monitoring and measurement data of the project are compared and analyzed to verify the reliability of the support measures.