Abstract: Based on the field model tests of tunnel-type anchorage in the Pulite bridge, the deformation and failure process of rocks surrounding tunnel-type anchorage are revealed via numerical simulation. The failure surfaces in the surrounding rocks initiate around the rear interfaces between the plugs and rocks, and propagate outward with a frustum shape. The failure mode is tensile-shear. Moreover, the rocks near the free surfaces in the front of the plugs are pushed outward and damage with tensile mode. The stresses vary complicatedly as the pullout force increases. Based on these, a computational mode of the pullout force for the surrounding rocks is proposed by establishing the equilibrium relationship of forces acting on the failure surfaces. Different from the published literatures, this mode embodies the “clamping effect”, and reveals the complicated variation of forces on the failure surfaces as well. It is necessary to execute field tests and numerical simulations in order to assess the values of the forces on the failure surfaces. In future, the possible shapes of the failure surfaces and the variation ranges of forces on the failure surfaces can be suggested after the accumulated studies for various rocks with different strengths and structures. The computational mode is verified by the testing results, and is used to estimate the pullout force of the prototype anchorage. The results show that the ultimate pullout capacity is very large. The design philosophy of the tunnel-type anchorages is considerably conservative nowadays. We believe that it is probable to apply the tunnel-type anchorages in moderate-strength and even soft rocks. The issues concerning the changes of failure surfaces in different rocks, the influence of rock structures on the pullout capacity, etc., are discussed.

Key words: tunnel-type anchorage, field model test, pullout mechanism, computational mode of pullout force, failure surface, clamping effect