Study On The Deformation Failure Mechanism And Stability Of The Surrounding Rock Of The Headrace Tunnel In Qinglong Hydropower Station

Qinglong Hydropower station is located at the in the upstream of the Baishuijiang River of sichuan jiuzhaigou county,which is a headrace tunnel station. Water power generation system is at the left bank of the Baishuijiang River,the length the headrace tunnel is ahout 14 km. the cross-section type of the tunnel is circular, the excavation diameter is about 8.8 ~ 9.9 m, the average vertical buried depth is about 130 ~ 370m,the biggest is 600m,the smallest is about 100m. the exposed stratum along the tunnel is mainly P1h,the stratum lithology is mainly thin layer ~ thick layer limestone,local is Slate, sandstone and carbonaceous thousand pieces. Due to the high strength, the quality level of the surrounding rock is prescribed higher (Ⅲlevel), Especially the porphyry granite rockwhich has high strength and good quality , it is a kind of engineering rock mass which worths making full use of . Based on the above anderstanding , the tunnel line should go through the stratum of porphyry granite as far as possible in the design. But it is found in the tunnel excavation process that the porphyry granite rock mass is broken, alteration is strong,the deformation of the surrounding rock is serious, collapse is occurred frequently; the deformation of the Layered rock-mass with special rock mass structure is strong, collapse is occurred sometime, Primary support facilities is destroyed seriously,which bring great threat to the engineering construction safety.In this paper, combined with Field investigation based on previous studies,it is summarize the engineering geological charateristics, construction and structure features of the rock mass, the deformation failure types and distribution. A ccording to geological environmental conditions and construction and structure features of rock mass ,using the water conservancy and hydropower engineering geology classification methods and combined with related various kinds of experiments data ,this paper puts forward the suggested value of physical and mechanical parameters of surrounding rock mass. Finally based on deformation and failure mechanics , combined with discrete element numerical simulation analysis method , this paper focuses analyzing the stability on the two type surrounding rock mass of the thin layer shape with limestone, slate and altered broken porphyry granite. the following are conclusions:1. The researched area is special tectonic area,the strong geological tectonic evolution and river valleys evolution are the indirect control factors which cause the deformation of the surrounding rock in the tunnel.2.The surrounding rock in the tunnel is mainlyⅢlevel in the section of the layer rock mass, whose stability is better ,partly isⅣlevel, whose stability is worse, and need to strengthen support measures;It is mainlyⅣlevel in the section of the porphyry granite rock mass,,partly isⅤlevel,the overall stability of surrounding rock is poor.3. The deformation and failure mechanism of the surrounding rock in the tunnel is divided into five types:①the type of bending fracture failure in the bucky layered rock mass of medium~thick layer, which performes "push rod stability problem" in mechanics;②the type of bending extrusion shear failure in the layered soft rock mass of thin layer ~ extremely thin layer;③the type of bending abscesses deformation in the layered soft rock mass of medium~thin layer;④the type of Shear slipping failure in the weak altered Porphyry granite rock mass;⑤the type of Shear fracturing loose in the weak altered brokenrock mass.4. Altered rock and rock mass structure are the main control factors to the stability of surrounding rock of the tunnel .Alteration mainly controls the stability of the surrounding rock through the physical and mechanical properties; rock mass structure of thin layer limestone, SLATE mainly does by changing their mechanical properties.5. 3DEC discrete element analysis software is used to do numerical simulation analysis on the deformation and failure process of the surrounding rock, with calculation analysis model based on two kinds of geological prototype rock of layered rock of special structure and broken altered granite porphyry (Ⅴ level), the simulation results retrieve properly the five kind of the deformation and failure mechanism,it is demonstrated the correctness of the theory analysis to the deformation and failure mechanism of the surrounding rock mass of the headrace tunnel in Qinglong Hydropower station from numerical simulation analysis Angle.Finally, according to the analysis theory and numerical simulation results, the tunnel excavation and supporting schemes are proposed.This paper analysis results have a certain reference significance for the problem of the deformation and failure mechanism of the surrounding rock mass in the headrace tunnel.with similar engineering geological conditions.