Research On Mechanics Of Earthquake Damage And Stability Of Seriously Damaged Tunnul Section In Earthquake-Prone Area During Construction Period

With the steady progress of Chinese Western Development strategy and the boom of high speed railway construction, more and more tunnels have to been built in earthquake-prone area in Western Sichuan. For a long time, the frequent earthquake damaged the rock mass structure of the crust surface and reduced the stability of the mountain. After suffering the strong and frequent earthquake, rock mass has become cataclasite. High development degree of the structural plane, poor combination between layers, and the wide distribution range of cataclastic rock mass have become the key factors of restricting the railway construction.Building a large railway tunnel in seismically active areas is inevitable to cross the cataclastic rock. In the shallow-buried section, fault fracture zone and high and steep slope of tunnel entrance, cataclasite after earthquake and the frequent earthquake left great potential hazards on the safety of tunnel construction. During the construction period in earthquake damage serious section, the dynamic stability of the supporting structure and the security control measures are lack of experience and few instances can be referred to, thus it needs to be researched and improved.This paper conducts related research based on the under-construction Pingan tunnel and Liutongzhai tunnel of Chengdu to Lanzhou high-speed railway, which across the Longmenshan active fault zones. Most tunnel surrounding rock in Chengdu to Lanzhou high-speed railway are cataclastic rock mass after earthquake. The lithology is mainly phyllite, which is intermediary and strong weathered sandstone. Full of fault and fractured surrounding rock, the phyllite is weakened when encountering water and the surrounding rock is complicated, which is quake-prone. During the tunnel construction period, the construction is affected by both the cataclastic rock after earthquake and the frequent earthquake. This paper analyzes the basic characteristic of the cataclastic rock after the earthquake and revised the tunnel surrounding rock grade of cataclastic rock in the area. Then, through numerical modeling, dynamic response characteristic of tunnels in earthquake seriously damaged area is studied. The safety during construction period is also been evaluated. The findings and research results are as follows.(1) Through plentiful literature and earthquake damage information, combining the condition in the construction site of Chengdu-Lanzhou high-speed railway, the basic characteristics, distribution regularities and engineering properties of the cataclastic rock after the earthquake has been found. The rock mass shatter level has been divided based on the shatter characteristics of cataclasite after earthquake under different shatter degree. Through BQ value reduction, the revised surrounding rock grade of cataclasite after earthquake has been established and used in practical project.(2) Through numerical modeling, dynamic response regularity and stability of high and steep slope in cataclastic rock area after earthquake under different earthquake intensity during the construction period have been analyzed. By using dynamic strength subtraction method, the safety of high and steep slope during construction has been evaluated.(3) Through numerical modeling, dynamic response regularity of shallow-buried section of the tunnel entrance in cataclastic rock area after earthquake and without earthquake under different earthquake intensity during the construction period has been analyzed. The safety of shallow-buried section of the tunnel entrance during construction has been evaluated.(4) Through numerical modeling, dynamic response regularity of tunnels in fault fracture zone in cataclastic rock area after earthquake and tunnels in normal area under different earthquake intensity during the construction period have been analyzed. The safety of tunnels in fault fracture zone during construction has been evaluated.