THE BEARING MECHANICS AND CAPACITY OF TUNNEL-TYPE ANCHORAGE

The study on the bearing behavior of tunnel-type anchorage is the one of the basic scientific questions in the design and application of this type anchorage. Tunnel-type anchorages look like inverted-shape structures with bigger bottom and smaller top. This geometrical characteristic may be the main reason that the additional stress could initiate on the interface of anchor and rock under the main cable load. In order to study the difference of bearing capacity of tunnel-type anchorage in different load stage, the formulas of bearing capacities of anchorage are built with the analysis of the change law of additional stress. And these formulas are verified by the results of field model test. We find that:the load stages of tunnel-type anchorage can be classified as original stage, elastic stage and plastic stage. And the value of initial bearing capacity of tunnel-type anchorage relies on the gravity of the anchor while the ultimate capacity depending on the failure modes and additional stress. Besides, the failure surface of the object anchorage happens on the interface of the anchor and rock. And the initial bearing capacity of the support project is 1540MN,seven times higher than design load. The ultimate bearing capacity reaches to 3080MN,fourteen times higher than design load. While the results obtained from the field model test are 9 and 13 times higher than design load respectively. The results tell us that the bearing position, the range of rock taking part in the different stage and the degree of rock holding the anchor are different in different load stage. Moreover, the stage characteristics of tunnel-type anchorage capacity are closely relevant to the additional stress. And the geological characteristic of tunnel-type anchorage improves the bearing capacity tremendously. Last but not least, the estimation formulas for the bearing capacity is agree with the results of model test and can be applied to guide the design of tunnel-type anchorage.