Study On Bearing Capacity Of Tunnel Anchorage In Large Suspension Bridge

In recent years, with the rapid development of traffic construction in China, long-span suspension bridge has been widely applied in the mountain and ravine region. As an important form of anchoring system in suspension bridge, the bearing capacity and its influence factors are the foundation of tunnel anchorage engineering design. Therefore, the thesis bases on the tunnel anchorage in suspension bridge in Dadu River and analyses its calculation method and influence factors of bearing capacity. The main research work is as follows:1) By using software MADIS-GTS, the 3D geological model was established with tunnel anchorages, highway tunnels, main pier and mountain body. Based on this model and three-dimensional finite difference software FLAC3D, the deformation of surrounding rock, distribution of normal stress and frictional resistance, distribution of plastic zone, and the failure mode of anchoring system were analyzed on four kinds of typical working conditions of super tension, limit super tension, cyclic tension of loading and unloading, and the long-term strength of surrounding rock, obtaining conclusions that the ultimate bearing capacity was seven times of cable force and the failure mode of anchorage system was shear failure along the interface of anchorage and surrounding rock. On the working conditions of the long term strength of surrounding rock and cyclic tension of loading and unloading, the deformation of surrounding rock was millimeters, distribution range of the plastic zone was less, and the bearing performance of anchorage system was fine.2) The distribution characteristics of plastic zone was obtained by the method of three-dimensional numerical analysis when the strength of surrounding rock decreased to 60%,50% and 40%., and it put forward that the anchoring system may appear unsymmetrical composite failure mode up and down the profile.3) The approximate theoretical formula was deduced respectively for the interface shear failure and composite failure mode. Compared with the result of numerical simulation, the calculative error of interface shear failure theoretical was 38%.. With the Calculation formula of composite failure mode, the bearing capacity of anchoring system based on the strength of surrounding rock decreasing to 100% 70%,60%,50%,40%,and the safety stock of anchorage system based on different cable force were calculated.4) The factors of bearing capacity of tunnel anchorage was analyzed by the method of numerical simulation, including the influence of elastic modulus of surrounding rock, the anchor axial Angle, the length of anchor and the anchor magnified angle. It is concluded that bearing capacity of anchorage system increased in different degrees of nonlinear law with each of these four quantities increasing. Based on the analysis of influence factors, the rationality of original design for tunnel anchorage of suspension bridge in Dadu river was analyzed which considered the variability of main influence factors, and the optimization scheme was put forward:the axial angle β=40°, the length L= 50 m, and the magnified angle α=3.6°The research of this article can provide guidance and reference for the design calculation of the tunnel-type anchorage in large-tonnage suspension bridge.