| Anchorage is one of the main bearing components of suspension bridge. Compared with gravity anchorage, tunnel anchorage has both advantages of small environmental disturbance and cost-effective, but due to the interaction mechanism between anchorage and rock is still not quite clear, a customed design method for tunnel anchorage hasn’t been formed. Based on the first railway suspension bridge of China, Jinsha River Bridge, by means of theoretical calculation, numerical analysis and model test, the thesis studies the tunnel anchorage on both the bearing mechanism and its calculation method. The main contents and achievements are as follows:(1) The engineering geological characteristics on the project site are summarized, and the macroscopic mechanical parameters of surrounding rock are determined, then the quality of the surrounding rock and slope stability are evaluated in this thesis, which provide a geological foundation for finite element analysis of tunnel anchorage.(2) According to model test, the characteristics of deformation influence area of tunnel anchorage is revealed, the functional relationship of load transfer curves of anchorage is established, and the calculation formula of interface shear stress between anchorage and surrounding rock is deduced. The results show that loads on the axis of anchorage transfer from end face to front face under the law of negative exponent function, and in the transverse direction, loads spread from the center to around. The test also reveals that shear stress distributes ununiformly along the axial of anchorage at the interface of anchorage and surrounding rock, the peak value locates at about one-third of anchorage length from the loading surface, then the shear stress decays gradually away from the loading surface. For flat type tunnel anchorage, the deformation influence area shapes as a cylinder, and for anti-skid tooth type, deformation influence area shapes like an inverted frustum.(3) Model test shows three-phase characteristic of load-displacement curve of tunnel anchorage, which are elastic deformation, elastic-plastic deformation and destruction. The test also shows varied failure modes will take place under different contact surfaces. For the flat type interface scheme, the failure mode is interface failure of anchorage wall, and for anti-skid tooth type, it will be trumpet inverted frustum failure mode. Results show anti-skid tooth candy can significantly improve the ultimate bearing capacity of tunnel anchorage, and radial anchor bolt can enhance the whole stiffness of the tunnel anchorage.(4) Based on ABAQUS, the elastic and brittle plastic damage constitutive model for rock is established, which has good performace on the tension-shear composite failure mechanism and the burst mechanical behavior of rock. The establishment of the model provides a basis for the study of real failure process of rock mass.(5) Damaged numerical analysis method is used to simulate the load rupture process of tunnel anchorage, and the analysis on the influence of buried depth to tunnel anchorage cracking mechanism is carried out. The calculation results are in good agreement with model test results, which further extend the achievement of model test.(6) Influence factors on bearing performance of tunnel anchorage are analyzed. The results indicate that some factors have positive effect on bearing capacity of tunnel anchorage, such as the properties of surrounding rock, the strength of anchorage body and the rock interface, the anchorage extension angle, axial length and cross section diameter, and others, for the rock classification and the axial length, exist threshold values. The sensitive degree of geometrical parameters sorts as:extension angle> section diameter> axial length. And the results also show that bearing performance of circular section anchorage is better than that of horseshoe cross section.(7) Four proposed tunnel anchorage failure modes are sumed up, namely interface damage of anchorage wall, surrounding rock damage (falls into inverted frustum shape and trumpet inverted frustum shape), sliding failure of whole slope and compression failure of anchorage. Then the certain conditions for every failure mode and their performance characteristics are given. The results provide a theory basis for the establishment of calculation model for tunnel anchorage.(8) Based on limit equilibrium theory, theoretical derivation are carried out upon two kinds of typical failure modes, interface damage of anchorage wall and surrounding rock damage of anchorage body, and calculation method of tunnel anchorage on its ultimate bearing capacity is proposed.(9) Calculation procedure and methods are proposed to the design of tunnel anchorage of railway suspension bridge. Combined with Li-xiang railway Jinsha River Bridge, a design example of tunnel anchorage is given. Relying on three dimensional finite element analysis of the project, this thesis gives a further verification on the rationality of the proposed calculation method and design theory. |
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