Study On Stability In Large-spanned Double-arch Tunnels Under Complex Geological Conditions

Based on monitoring measurement and numerical simulation for Shangpo double-arch tunnel on Tongling-Huangshan highway, the author try to study the stability problem in construction of double-arch tunnel under complex geological conditions, and the principles of New Austria Tunneling Method about dynamic construction and dynamic design can be true.Firstly, the monitoring plan and monitoring result in construction of large-spanned double-arch tunnel is introduced systematically. The distribution of stress and deformation of perimeter displacement, deformation rate, ground surface settlement, load of initial support, load of secondary lining of surrounding rock and axial force of anchor bolt are carried out during the tunnel construction. The genetic reason of anomaly in construction of double-arch tunnel was analysed combined with the in-situ monitoring result.Secondly, by building boundary element model of tunnel structure, the whole process of different construction steps for double-arch tunnel is simulated in 3D-FSM·DDM source program. Then, BEM analysis of cross section K151+010 is carried on. The analysis shows that interactive influence on constructing sequence of double-arch tunnel is generated. The construction plan of firstly excavating shallow tunnel is more feasible for deformation displacement of tunnel surrounding rock and stability of extensional organization.Thirdly, by transplanting model of elastic fault constitutive relation, the whole process of excavating tunnel under the condition of existent or nonexistent fault is simulated in 3D-FSM·DDM source program. Then, contrastive analysis of cross section K151+010 and K151+ 071 is carried on. The analysis shows that the stress, displacement and stability of surrounding rock under the condition of existent fault have obvious difference in comparison with the tunnel of nonexistent fault. The poor geological phenomenon near tunnel should be considered before designing tunnel.Fourthly, by contrastive analysis between monitoring result and simulated result the research results are verified mutually and the insufficiency and error in studies are avoided, which provide some help for design and construction of analogical tunnel.