关键词: tunnel with large extrusion deformation, primary support, rheological effect, support resistance, layered support

Abstract: Currently, the support parameters and timing are difficult to be quantified in the design of tunnels with large extrusion deformations. Therefore, considering the rheological effect of the surrounding rocks and the plastoelastic constitutional relations of supports, the equivalent support resistance of various types of support is numerically analyzed, along with the quantitative parameters and adaptability of layered primary supports for tunnels with different extents of large deformations. The main conclusions are as follows: (1) By controlling the compressive strength, the equivalent support resistances of shotcrete and steel arch are proposed with different combined parameters. Based on the principle of displacement equivalence, the equivalent support resistances of grouted bolts (with different diameters and lengths) and prestressed anchor cables (with different lengths) are proposed. (2) According to the monitoring curves, the physicomechanical parameters of the surrounding rocks are inverted to calculate the characteristic curves of the surrounding rock considering the rheological effect. This can depict the relationship among the deformation of the surrounding rocks, the support resistance required by different support timing, and the time. (3) According to the existing cases, 〖HJ1.5mm〗15 cm is taken as the deformation limit of singlelayer support to obtain the support resistance curves. Based on the principle of deformation limit control, it is recommended that the support form of singlelayer primary support + shortanchor rods should be used for slightlylarge deformations, the support form of twolayer primary support + shortanchor rods should be used for moderatelylarge deformations, and the support form of circular tunnels + threelayer primary support + shortanchor rods + longanchor cable should be used for extremelylarge deformations. The support timing and reserved deformation values are also proposed for different levels of large deformations. (4) The recommended schemes have been applied to the Muzhailing tunnel of the LanzhouChongqing railway, and the results demonstrate that the recommended schemes are feasible.