Estimation method of ultimate bearing capacity of tunnel-type anchorage based on simplified mechanical model

The design philosophy of suspension bridge tunnel-type anchorage is that anchorage and rock bear the bridge load together. As the cooperative bearing mechanism of anchorage and rock, its bearing capacity is much higher than that of gravity anchorage with the same volume. However, due to the insufficient understanding of the synergy of surrounding rock, the squeezing effect between the anchorage and rock mass is still conservatively ignored in the design of tunnel anchorage. In order to understand the mechanism of coordinated bearing between anchorage and rock mass, and reveal the essence of improving the bearing capacity of tunnel anchor, a simplified mechanical model of tunnel anchor was established by analyzing the whole process from construction to completion of the bridge. Mindlin stress solution was used to analyze the law of load transmission along the anchorage axis and the distribution of compressive stress between anchorage and rock mass caused by load. A simplified method for estimating the ultimate bearing capacity of tunnel type anchorage was proposed. Then the recommend estimation method was successfully applied to Wujiagang suspension bridge project. The main conclusions are as follows: the interface force between anchorage and rock mass is mainly produced by the self weight of anchorage and the mutual extrusion of anchorage and rock mass; the additional stress at the interface between anchorage and rock mass increases first and then decreases from the rear anchor face to the front, and reaches the peak stress at about 1/3L away from the rear anchor surface; the ultimate bearing capacity of the tunnel anchorage of Wujiagang Yangtze River Bridge calculated by the allowable shear strength is 3 504 MN, about 16 times of the design load, which is basically consistent with the laboratory model test value.