Research On Analysis Of Collapse Mechanism And Construction Technology Of Tunnel In Fault Fracture Zone

As an important connection hub of the highway network,tunnel engineering is playing an increasingly important role in engineering construction.During the excavation of deep and long tunnels,various complex geological conditions,such as fault fracture zones,will inevitably be encountered.Geological disasters such as tunnel landslides also occur from time to time.It is of great significance to study the collapse mechanism of tunnels as they pass through fault fracture zones and how to avoid tunnel collapses.Based on the Yingerling Tunnel crossing the F18 fault fracture zone as the engineering basis,and taking the 9.30 collapse event as the engineering background,combined with site survey,numerical simulation and other means,the tunnel collapse mechanism was analyzed from the aspects of geological structure and surrounding rock deformation mechanism.The numerical simulation was used to further study the reinforcement effect of the advance reinforcement scheme for the tunnel in the fault zone,and the advance reinforcement parameters were analyzed.The main research contents and conclusions are as follows:(1)Theoretical analysis of the collapse mechanism of the Yingerling Tunnel was carried out through on-site geological surveys and special geological disaster detection methods.It was found that the strength of the broken surrounding rock in the fault fracture zone was low,and the tunnel excavation resulted in stress concentration and sudden increased stress,exceeding the shear strength of the surrounding rock,which caused the roof to collapse.At the same time,the effect of groundwater reduces the cohesion of the surrounding rock and the internal friction angle,which causes the shear strength of the surrounding rock to be greatly reduced,weakening the self-stabilizing ability of the surrounding rock,and intensifying the collapse of the tunnel.(2)Through numerical simulation,it is found that the displacement of the surrounding rock in the fracture zone of the interrupted layer during tunnel excavation is greater than that in other areas.The plastic zone of the surrounding rock within the fault fracture zone can extend to within 4m in front of the construction palm face,and the plastic zone of the surrounding rock outside the fault fracture zone extends to within 2m in front of the construction palm face.(3)Based on a comprehensive comparative analysis of two advanced reinforcement schemes of advanced bolts and advanced grouting small ducts,it is concluded that the small grouting ducts treat the tunnel vault within the fault fracture zone and the surrounding rock at the left and right arch waist The effect is better than that of the lead bolt.And the advanced grouting small ducts has a better effect on the surrounding rock at the vault than the left and right arch waists.(4)The optimization research on the advanced grouting small ducts shows that the grouting reinforcement zone with a thickness of 1m ~ 3m can reduce the arch settlement of the tunnel in the fault fracture zone by about 43.35%,53.28%,and 57.41%,respectively.It can be seen that the thickness of the grouting reinforcement area has increased to a certain extent,and its reinforcement effect on the surrounding rock of the vault is becoming more and more limited.Therefore,comprehensive consideration of economy and safety,the tunnel excavation in the fault fracture zone adopts the advance grouting small pipe,grouting reinforcement area 2m thick(the length of the small pipe 4m,30°external plug angle)advanced reinforcement scheme.