Analysis On Stability Of Intersection Part In Deep-buried Diversion Tunnel With Small Section

Branch tunnel usually plays a supporting role in the construction process of long-distance and deep-buried diversion tunnel with small section.Nevertheless,Surrounding rock stress will redistribute due to the excavation of main tunnel at the intersection of the diversion tunnel and construction tunnel,which has an influence on the stability of the intersection.Not only the stress characteristics of surrounding rock,but the stress and deformation characteristics of supporting structure are complicated.Accordingly,relying on the diversion tunnel project in Rizhao,analytical investigation on stability of intersection part of the deep-buried diversion tunnel with small section has been conducted with numerical simulation method combining with field date.(1)The applicability of several kinds of rock strength criterion in the calculation process was analyzed in this thesis.Calculation principle and usable range of the finite element software MIDAS/GTS has been expounded in detail.(2)Three dimensional dynamic simulation of this project construction process was carried out utilizing MIDAS/GTS,on the basis of which,the influence on the stress and displacement of surrounding rock and the stress characteristics of support structure due to main tunnel excavation were analyzed.The analysis results showed that the excavation of main tunnel has a great influence on rock stress of the wall and arch foot on the sharp angle side of the intersection within the distance of 5 meters.Further more,the extent of the impact of main tunnel excavation on surrounding rock of branch tunnel is limited to a certain area within the distance of 5 meters from the intersection.(3)Based on the simulation model and methods of previous numerical calculation,the intersection angle between the main tunnel and the construction tunnel was changed into skew(60°)and orthogonal(90°)to do a research mainly focus on the changing characteristics of the stress anddisplacement of surrounding rock and the stress of supporting structure in intersection.The calculation results showed that,the stress and displacement of surrounding rock and stress of supporting structure in the intersection both decreased with the intersection angle.And the intersection angle has a great influence on the maximum principal stress of the side wall in the intersection part.(4)Tunnel inner space convergence,internal displacement of surrounding rock and monitoring data of axial force of anchor bolt were analyzed.And internal space convergence monitoring data was fitted with nonlinear regression method.Meanwhile,the law of convergence deformation of tunnel was predicted.