Abstract: Tunnel type anchorage has wide application range in the building of suspension bridge as it is more economical and environmentally friendly than gravity anchorage. The tunnel type anchorage of a large-span suspension bridge on a railway in southwest China bears a super-large main cable load of 430,000 kN in the IV-V grade engineering rock mass. In the present research, the cave forming characteristics and the surrounding rock response characteristics under the main cable load and overload of the tunnel type anchorage were analyzed by using 3D numerical simulation method. Results unveil that according to the current support design, the fractured rock mass is in a state of slight squeezing deformation after the excavation of anchorage hole. The surrounding rock of tunnel type anchorage mainly displays elastic deformation under main cable load, and the displacement increment of the anchor plug body is only a few millimeters. The deformation of surrounding rock is significantly affected by the lithology of the stratum, and the gradient of surrounding rock displacement around the anchor plug body is large. Under overload, the plastic zone of surrounding rock of the anchor plug body gradually develops from the back anchor surface to the middle and front part along the surrounding rock of the anchor plug body, and the final failure mode is the shear failure of surrounding rock from the back anchor surface to the front anchor surface of anchor plug body. Tunnel type anchorage structure also has strong adaptability to rock mass environment with inferior basic quality.

Key words: fractured rock mass, large-span suspension bridge, tunnel type anchorage, cave forming characteristics, bearing characteristics, overload capacity