Research On Development Characteristics And Prevention Measures Of Unstable Rock At Taoping Tunnel Exit Along Wenchuan-Barkam Expressway

Along the Wenchuan-Barkam expressway,the terrain is steep and the exposed lithology is mostly phyllite.Due to the poor stability and easy weathering of phyllite,a variety of unstable rocks have developed along the expressway.In this paper,the unstable rock at Taoping Tunnel Exit along Wenchuan-Barkam expressway is taken as the research object.Based on the field geological investigation,combined with a series of analysis methods such as sterographic projection analysis,limit equilibrium calculation and numerical simulation,to grasp the development characteristics and stability of the unstable rock,and put forward the control measures.Specific content as follows:1.The unstable rock of Taoping Tunnel Exit is distributed in a strip.According to the general situation of unstable rock,it is divided into four unstable rock zones(WYD1,WYD2,WYD3,WYD4).In WYD1 and WYD4,there is an unstable rock mass(WYT1 and WYT2).The control boundary are formed by the posterior edge crack and the bottom dipping structural face of the two unstable rocks masses,they are concluded that the instability mode are sliding.2.The limit equilibrium method is used to obtain that WYT1 and WYT2 are in stable states under natural conditions and rainstorm conditions.While under earthquake conditions,WYT1 and WYT2 are in an unstable state.Furthermore,UDEC was used to simulate the deformation and failure process of WYT1,the results show that under natural conditions,the leading edge of WYT1 is locally unstable,but the failure scale is small and the overall stability is good.Under earthquake conditions,the WYT1 rear edge crack and the bottom of the dipping structural face through,the failure scale is large and the overall stability is poor.3.By using the traditional formula and ROCKFALL simulation software to calculate the motion characteristic parameters of WYT1 and WYT2,such as the bounce height,translational velocity and total kinetic energy.Meanwhile,the threat range of rockfall was determined.4.Based on the results of field engineering geological investigation and laboratory analysis,put forward the reasonable and feasible protection measures for the unstable rock areas:(1)The unstable rock masses were treated with remove-drainage-anchorage-hanging active protection net and pouring concrete.(2)Slope cutting,then hang the active protection net and passive protection net.The passive protection net with a length of about200 m is set up at an elevation of about 1650 m to prevent rockfall.(3)For the side of the tunnel exit,there is no open interval of the rockfall,set retaining wall and passive protection net.(4)It is suggested to lengthen the opencut tunnel and adopt the measure of flexible steel shed hole.