Study On Hydraulic Criterion Of Fracture Zone In Deep Buried Tunnel

With the rapid development of China's transportation and water conservancy and hydropower projects,a large number of tunnels are being or will be built.Water inrush is an engineering geological disaster,which is often encountered in tunnel construction and has the characteristics of ‘strong burst,high stress and high water pressure'.Water-rich fault fracture zone is one of the main controlling factors leading to tunnel water and mud inrush.The prevention and control of this kind of disaster has been widely concerned by scholars at home and abroad,and the determination of the minimum safe thickness of water-resistant rock mass is the key.Based on the Qilianshan tunnel as the engineering background,this paper studies the evolution law of water inrush and mud-burst catastrophe through the water-rich fault fracture zone through theoretical analysis,model test and numerical simulation,and discusses the minimum safe thickness of the water-resistant rock mass.At last,some research results with theoretical and engineering value have been obtained.(1)Based on the silo theory and limit equilibrium method,the mechanical model of water inrush in the fault fracture zone with the tunnel axis and the plane of the hand were established,and the mechanical criterion of water inrush and mud inrush in the water-rich fault fracture zone was obtained.The influence of the width of the fault fracture zone on the minimum safe thickness of the water-isolated rock plate was analyzed.The results show that the width of fault fracture zone has a significant influence on the determination of the minimum safe thickness of the water-resistant rock mass when the width of the fault fracture zone is less than 200 m.The research result was applied to the Yonglian tunnel and the Qilianshan tunnel.After calculation,the minimum safe thickness of the water-resistant rock mass of Yonglian tunnel is 7.34 m.Water inrush occurred in Yonglian tunnel because of insufficient safe thickness.The minimum safe thickness of the water-resistant rock mass value of F6 and F7 faults in Qilianshan tunnel are respectively 10.22 and 11.59 m.In the construction of Qilianshan tunnel,it is safe to pass F6 and F7 faults with the 12 m water-resistant rock mass.It is shown that the theoretical calculated value is relatively close to the actual value and has a certain reliability.(2)Based on the multi-functional large-scale model test system independently developed by the research group,the model test of tunnel water inrush and mud disaster is carried out.Simulating the disaster process of water inrush from the fracture of the Qilianshan tunnel through the F7 fault fracture zone.Through the excavation of the medium seepage pressure and earth pressure,the displacement changes in the process of water inrush and mud disaster,and the physics field before the disaster occurs has a very strong response.(3)Through the model test,the minimum safe thickness of the water-resistant rock mass in the Qilianshan tunnel crossing the F7 fault fracture zone is 10 m,and the derived mechanical criterion based on the silo theory is 9.66 m,which is in good agreement with the model test values.The rationality and accuracy of the hydraulic criterion of water inrush in fault fracture zone based on silo theory are verified.(4)The 3DEC numerical simulation software is used to analyze the influence of factors such as fault fracture zone width,water pressure and buried depth on the minimum safe thickness of the water-resistant rock mass when water inrush occurrs.The results show that the relationship between the minimum safe thickness and water pressure is proportional.The greater the water pressure,the greater the minimum safe thickness.The minimum safe thickness is proportional to the width of the fault fracture zone.The influence of the buried depth on the minimum safe thickness is that the minimum safe thickness decreases with the increase of the buried depth,which is approximately inverse proportional function.With the increase of the buried depth,the decreasing trend of the minimum safe thickness is obviously smaller,and the influence ability is reduced.The simulated value is slightly smaller than the theoretical value.respectively.Finally,the numerical simulation results can be well consistent with the theoretical derivation,which further verifies the rationality of the theoretical results.