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Abstract In order to investigate the clamping effect and failure pattern of surrounding rocks as well as the limit of the pullout capacity of tunnel-type anchorage，field model tests on the conical frustum anchorage and cylindrical anchorage were conducted inside two parallel caves within the oblique cave of exploration in the anchorage area of Puli bridge. The side surface areas and the heights of two anchorage models are identical for quantitative comparing the differences of the clamping effect of surrounding rocks. The magnitude and the range of deformation before failure and the limit of load for the conical frustum anchorage are considerably larger than those for the cylindrical anchorage due to the clamping effect. For the cylindrical anchorage，brittle failure occurs remarkably in the contact area between the anchorage concrete and the surrounding rocks. For the conical frustum anchorage，the failure of the surrounding rocks occurs along the unfavourable fractures and experiences a long period of yielding deformation. The failure patterns for two anchorages are quite different. A concept of the coefficient of clamping effect and a corresponding method of calculation were suggested. The coefficients of clamping effect in the elastic period and at the period of strength limit are found to be 4.48 and 4.54 respectively. The pullout capacity induced by the clamping effect is significantly larger than the effect caused by the shear strength between the concrete and the rock mass. The clamping effect is the primary factor accounting for the pullout capacity of tunnel-type anchorage.
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Received: 12 December 2013
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2015, Vol. 34 
