Research On Surrounding Rock Stability Of Diversion Tunnel At Liujiaxia Hydropower Station

At present,with the rapid and continuous development of China's national economy,public infrastructure project construction is also proceeding in an orderly manner.As part of it,the hydraulic tunnel plays an important role in the transmission of water and flood discharge.The diversion tunnel of the Liujiaxia Hydropower Station is about 31.71 km long,which is an extremely long tunnel with a depth of more than 600 m and a maximum buried depth of about 1000 m.It is a deep tunnel.The geological conditions of the tunnel are relatively complex.Tunnel excavation may have engineering geological problems such as the stability of surrounding rock,rock burst with high ground stress,deformation of soft rock,water inrush,mud,high ground temperature,radioactivity,and harmful gases.Combining so many possible problems,we can see that it is necessary to study the stability of tunnel surrounding rock and solve construction,design,and future operations.Taking the water diversion tunnel of the Liujiaxia Hydropower Station as an example,this paper studied the engineering geological conditions of the tunnel site based on the field practice,collected and consulted data,and carried out engineering geological segmentation and surrounding rock classification along the TBM2 section of the tunnel.Finally,the two-dimensional numerical simulation of the section of tunnel exit section was conducted through Midas software to study the stability before and after tunnel excavation support.The main achievements are as follows:(1)Through the study of the engineering geological conditions in the tunnel area,the tunnel geological engineering conditions are taken into account to prepare for the segmentation of the tunnel TBM2 section.(2)First,segment the engineering geology of the TBM2 section,and then draw the rose pattern of each section of the structural plane.Through the relationship between the structural plane direction and the direction of the axis of the tunnel,determine whether the stability of the tunnel is favorable and the grade of the surrounding rock Structural surface score parameter E,and then complete the geological classification of tunnel surrounding rock.It can be seen from the classification results of the surrounding rock quality that the surrounding rock of the TBM2 section of the diversion tunnel is dominated by type II surrounding rock,followed by the type III surrounding rock,and the rock mass is of good quality.The surrounding rock is divided into faults when passing through F3,F4,and F8 faults.Class V,rock mass is poor.(3)Select different sections of the outlet section and different grades of surrounding rock and the corresponding supporting parameters.Use the Midas software to perform two-dimensional numerical simulation.Displacement characteristics of the surrounding rock,the main stress of the surrounding rock,and the strength of the shotcrete,respectively.The axial force of the bolt,the plastic area of the surrounding rock and the depth of influence were analyzed,and the relevant laws were obtained.(4)The common geological problems that may occur in diversion tunnels are introduced.The specific problems can be divided into the problems of tunnel water inflows: the calculation of TMB2 water inflow using the atmospheric precipitation infiltration estimation method and the Tuibuyi formula;tunnel soft rock deformation and disintegration problems: the use of modified Fenner-Tarobo and other related formulas calculate radius and radial deformation of the plastic zone;deep-buried tunnel rock burst problem: use the rockburst criterion formula proposed by Prof.Hou Faliang to calculate the critical rockburst depth and classify the grade according to the specification,Finally put forward suggestions for prevention and control measures.