Research On The Stability Of Soft Rocks Around Entrance For Shallow Bias Tunnel With Super Large Cross-section

At present，super-large cross-section flat tunnels that cross-sectional area ismore than150square meters are still quite rare among all Chinese road tunnels. Sincethe cross-section is super large，compared with usual tunnels, the flat rate is muchhigher，and the sensitivity of tunnel on the issue of bias is increasing as well，Thisthesis will further study on surrounding rock’s stability around entrance ofsuper-large cross-section shallow-buried bias tunnel excavated by two-side pilotdrifting method，on the background of domestic rare large-span and super-largesection tunnel---FuQuan Highway extension project QianOu Tunnel and based on theresearch methods that Combining in-situ test with static finite element analysis. Someresearch fruits and conclusions are obtained as follows:1.Using two-dimensional elastoplasticity finite-element analysis with softwareANSYS10.0, to study transformation rules and stress of super-large cross-sectiontunnels’ surrounding rocks and supporting structures, which are constructed by twoside-wall pilot tunnel method to get demarcation of shallow and unsymmetricalsuper-large cross-section tunnels.2.To make a test scheme accordingly with thoughtful consideration of QianOutunnel’s characteristic that is shallow and unsymmetrical, super-large cross-sectionalas well as the site condition of tunnel portal. Some initial results of the research havebeen obtained through monitoring measurement test on the process of tunnelexcavation. Researching into those data, the general law of surface settlement anddeformation of surrounding rock was obtained.3.According to the actual situation of QianOu tunnel, a three-dimensionalnumerical model was established, and the applicability of this model was verified bycrossing experimental data，via this model the excavation process of the tunnel wassimulated. By analyzing the safety factor of surrounding rock and stress radius ofinfluence as well as strength response and displacement rules of surrounding rock,lining, falsework and bolt to evaluate the stability of surrounding rock and the safetyof supporting structures. And the evaluation give theory basis to safety and success ofthe tunnel construction. 4.Through comparing and analyzing class-V surrounding rock and surroundingrock under soil soft rock as well as the stress deformation of supporting structure, astudy is made on the differences of their stability.