Analysis On The Long-term Safety Of Tunnel Structure With High Ground Stress Considering Surrounding Rock Creep

With the rapid development of China's economic and social and the rapid development of the west regions,there are more and more tunnel projects in the western mountainous areas.Most of these tunnels have the characteristics of long,large and deep buried.Due to the influence of the tectonic stress field,the creep effect of the surrounding rock will increase the external load of the lining structure with the increase of time,which will affect the safety of long-term service.With the Lanjiayan Tunnel as engineering background,the influence of surrounding rock creep on long-term safety of tunnel structure is studied by means of theoretical analysis,laboratory test and numerical simulation.The main research contents are listed as follows:1.Based on the rock mechanics system and the acoustic emission testing system,the mechanical properties of the deep buried carbonaceous slate under different confining pressures and different water states are analyzed by using uniaxial and triaxial compression tests.The study finds that water has obvious softening effect on mechanical properties and fracture characteristics of carbonaceous slate.The mechanical parameters of carbonaceous slate increase with the increase of confining pressure.Under the condition of low confining pressure,the strength of rock is low,and the fracture of rock is more rapid and sudden.Under the condition of high confining pressure,the progressive fracture of rock is more obvious,and the ductility is enhanced2.Three-dimensional simulation model of stratum structure is established by using the Fast Lagrange finite difference software.Based on M-C yield criterion,the Burges creep model(Cvisc model)is adopted to consider the influence of surrounding rock viscoelastic and plastic effect on the long-term safety of tunnel structure.Based on the model,the influence of different tectonic stress fields on the long-term safety of secondary lining structure is analyzed.The results show that tectonic stress field has a significant impact on the long-term safety of secondary lining,and there is a significant difference between the position and the service life of secondary lining under different tectonic stress.3.Based on the three-dimensional simulation model,the influence of surrounding rock creep on the safety performance of secondary lining is studied.In the numerical model,the interface element is used to simulate the crack of secondary lining,and the cracking degree of the lining is expressed by using the stiffness reducing coefficient ?.In considering of the different cracking degree of secondary lining and the combination of the number of cracks and the location of cracks,the variation law of the internal force and safety factor of secondary lining structure under different working conditions is analyzed.The results show that the degree of crack has an obvious impact on the safety factor of the crack location,but it has little influence on the safety factor of the non-cracking location.The safety factor of secondary lining decreases with the increase of the number of cracks.There are significant differences between the position and reinforcement time of secondary lining under different cracking conditions.