Study On Instability Mechanism And Control Measures Of Brittle Fractured Surrounding Rock In High Geostress Tunnel

With the rapid development of China’s transportation infrastructure,more and more mountain road tunnels have begun to emerge.These tunnels are long in length,deep in burial,and have large initial stresses.After blasting and excavation,the stability of face rock can be affected by complex geological conditions.Especially when the tunnel crosses the structural fracture zone,the face rock and the unsupported rock are prone to collapse under the disturbance of excavation,which brings great threats to tunnel construction and personnel safety.Therefore,in combination with the actual construction and operation of the Micangshan tunnel,the quartz diorite,tunnel stability,collapse and intelligent monitoring of the tunnel operation period were carried out,which not only provides technical support for the solution of the specific engineering problems of the Micangshan tunnel,but also has important practical significance for ensuring the quality of the specific project,construction safety and optimization of design.In order to ensure the safety of tunnel construction,improve construction efficiency,propose long-term monitoring and support control measures and provide scientific research methods in high geostress tunnel surrounded by brittle hard rock,this paper will study the instability mechanism and control measures of these tunnels through indoor experiments,theoretical analysis,numerical simulation,on-site observation,detection and monitoring,and engineering example analysis.The main research methods,contents and results are as follows:（1）Through the uniaxial and triaxial compression tests of quartz diorite in the Micangshan tunnel,the stress-strain curves,macroscopic fractures and basic rock mechanics parameters under different confining pressures are discussed.And rock failure process is analysis by EA test.At the same time,using PFC^2D to simulate the compression test,which can reveal the micro-mechanical characteristics and micro-fracture evolution process of rock,and verify the consistency with laboratory tests.（2）Based on the minimum energy mechanism of rock mass failure,and combined with the geological conditions of the Fw2 structural fracture zone in the high geostress section of the Micangshan tunnel,FLAC^3D is used to simulate tunnel excavation which based on Hoek-Brown strength criteria.Then,the mechanism of excavation instability,rock failure mechanism and tunnel collapse evolution process are discussed.In order to propose more suitable control measures,studying the tunnel stress,plastic zone,vertical displacement,etc.under different working conditions.So,the recommended values for bolt support,tunnel second lining distance,and excavation footage are given.（3）Establishing an intelligent monitoring system for the operation tunnel by installing the force monitoring instruments of supporting structure during the construction period.So,the structural strength of the tunnel and the health of the supporting structure can be easily obtained.At the same time,the possible dangers of the tunnel can also be warned.