The Bearing Capacity Test Of The Tunnel-type Anchorage In Soft Rock Under Water Effect

Tunnel-type anchorage is one of the important components of the suspension bridge, its role is to hold the main cable on the rock or soil shore and its stability directly affects the post-operation and safety of the suspension. With the reservoir water level of bridge shore rising, the stability of the slope of banks in reservior and the bearing capacity and deformation of tunnel-type anchorage on slopes can be affected.To evaluate the safety and ensure normal work of anchorage under the influence of the rising reservoir water level of bridge shore has importantly social and economic significance. This thesis regards Jijiang Yangtze River Suspension Bridge's tunnel-type anchorage as research object with the anchorage built in soft rock. Soft rock can be significantly softened by water effect. In order to properly evaluate the security and stability of tunnel anchorage in normal use and long-term operation process, this paper,by means of model test, theoretiacal calculation and numerical simulation, studies the tunnel anchorage on both the bearing capacity and its stability under influence factor of water. The main contents are as follows:1 The theoretical derivation based on limit equilibrium theory are respectively carried out for two kinds of typical failure modes(mode one is interface damage of anchorage wall and mode two is surrounding rock damage of anchorage body). Based on mode one, the theoretical calculation of ultimate bearing capacity of Jijiang Yangtze River Suspension Bridge's tunnel-type anchorage is 7.58 × 105 kN and its stability safety factor is 7.01; based on mode two, the theoretical calculation of ultimate bearing capacity of the natural state model anchorage is 2333 kN, which is close to the model test of the maximum bearing capacity(2400kN).2 Two model tests of tunnel-type anchorage with 1:30 geometrical scales were conducted Two models owns different states of moisture content. One model is natural state, the other model is soaked state. By studying the deformation, ultimate bearing capacity and failure mode of anchorage and surrounding rock in the drawing load before and after the anchorage soaked, main conclusions can be drawn.The displacement of surface and borehole measuring points of the soaked state model is bigger than the natural state, which shows that water can obviously soften the deformation of the anchor model. The ultimate bearing capacity of natural state model anchorage and soaked state model anchorage respectively is 2400 kN and 1872 kN, which illustratesthat the bearing capacity of tunnel anchorage has a decline of 22% after the anchorage soaked. Two models have similar failure modes and damage area of the rock mass is similar to plug body?3 Based on the test results of the two models, mechanic parameters of surrounding rock mass of two model anchorages getting close to the scene were obtained by using ABAQUS to calculate the whole loading process of the two numerical models, combined with the method of uniform design applied to inversion scheme of basic mechanical parameters of the surrounding rock mass.The inversion parameters were brought into ABAQUS to calculation the natural state and the soaked state model. Compared the numerical results with field moeld test results, the results show that the numerical calculation and test results are close, which proves the reliability of numerical analysis method.4 By using ABAQUS software to study the influence of the slope water level variation on the bearing capacity of anchorage, some conclusions can be drawn: Due to the softening effect of water on the anchor locus' s wall rock, the bearing capacity of the anchorage gradually reduces from the normal water level to the highest flood level and the ultimate bearing capacity of the anchorage in the normal water level, the Yangtze River Xiaonanhai water level and the highest flood level is 10P(P is design load of single anchorage and its value is 108MN), 9.24 P, 8.17 P, respectively. When cable force is 1P, some parts such as the upper rock mass above the rear end of anchorage and the vault of anchorage appear small plastic zone from the normal water level to the highest flood level, but no plastic zone penetrates. It shows that the overall wall rock is in flexible working state. Rising water level increases the displacement and stress of the tunnel-type anchorage, but does not affect the overall stability of the tunnel-type anchorage.