Study On Construction Space-time Effect And Optimal Supporting Time Of Large Span And Flat Multi-arch Tunnel

With the increasing road traffic, six-lane multi-arch tunnel are builded in large quantities. for the six-lane multi-arch tunnel, on the one hand, it has the characteristics of excavation large span and section flat, it is large span and flat multi-arch tunnel, on the other hand, due to the interaction of its more construction process and left-right hole construction during the construction process, surrounding rock will be repeatedly disturbed and lining structure will also impact many times by the construction. Therefore, its stress and deformation is extremely complex, there is difference form the four-lane multi-arch tunnel or separated tunnel on construction space-time effect and secondary lining supporting time and, at the same time, it will bring on surrounding rock collapse or lining cracking and other quality and safety incidents during the tunnel construction process. The paper combine the transportation science & technology GuangDong province project"Research on Design and Construction Key Technique of Large Section Multi-arch Tunnel"(200700021), rely on the six traffic lanes multi-arch tunnel of Guanghe freeway, through theoretical analysis, indoor experiments, three-dimensional numerical simulation, similar model test, field monitoring test and other means, has systematic in-depth study on construction space-time effect and optimal supporting time for the large span and flat multi-arch tunnel, include the following study content:1. Rely on the support engineering, through the site monitoring, statistics and the regression analysis, the displacement-time effect and supporting structure stress-time effect be studied, and carry through the optimization anti-analysis based on APDL parameters, get the actual development rule of the support engineering surrounding rock deformation and supporting structure stress space-time effect, supervise the design and construction of the support engineering, and get surrounding rock main mechanical parameters for the model test and numerical simulation.2.Through the"CTSSSRH", large-scale Model testing for simulate the whole construction process of different surrounding rock and different excavation condition of large span and flat multi-arch tunnel is experimented, the testing successfully simulate preexisting displacement of internal tunnel face surrounding rock before tunnel excavation and elastic-plastic displacement of excavation instantaneous and creeping deformation after the excavation, reveal the whole process of surrounding rock three stages deformation, and analysis the development rule of displacement and stress. For the preexisting displacement before excavation and the stress release ratio is approximate equality,Ⅳclass surrounding rock is about 15～20%,Ⅴclass surrounding rock is about 20～25%.3.The three-dimensional finite element numerical simulation be performed, simulateⅤclass andⅣclass excavation space-time effect, and the middle wall dynamics construction mechanics ofⅣclass surrounding rock, analysis the space-time variation rule of surrounding rock displacement, surrounding rock and support structure stress, yield level coefficient and other, and dynamics mechanical behavior of composite curved middle wall, find the displacement release ratio of excavation current step and before excavation step under all class surrounding rock conditions.4. Base on the theory analysis of optimal supporting time, put forward the secondary lining supporting time determination method that according to"the support resistance minimum"principle, and found on the site monitoring of supporting resistance. And base on measurement of relying engineering, put forward the supporting time determination criteria of"displacement release ratio 87%, deformation rate 0.11mm/d"for large span and flat multi-arch tunnelⅤclass surrounding rock.5. For large span and flat multi-arch tunnelⅤclass surrounding rock, respectively calculation and analysis the supporting time through the follow four methods: resistance of support, deformation ratio, ultimate displacement, visco elastic plastic FEM, and comprehensive calculate the results of various methods, secondary lining optimal supporting time suggest take 20~25d, distance from the tunnel face suggest to take 35~45m.