Analysis of anchorage performance on new tension-compression anchor： Ⅰ simplified theory

The anchorage mechanism of a new tension-compression composite anchor is studied based on the assumption of triangular distribution of the shear stress between anchorage body and rock mass. The formula for calculating the uplift bearing capacity of the tension-compression composite anchor and the bearing capacity ratio of tension-compression composite anchor to tension type anchor (BCA) are derived. The analysis results for BCA show that the value of BCA increases with the increase of the anchorage length. BCA has the maximum value of 2.0 when the anchorage length coefficient k₁ = 2.0. The curve, which is like a bowl, of BCA is symmetricalyl distributed over the compacted anchorage length coefficient k₂. The value of BCA increases first and then decreases with the increase of k₂, and it has the maximum value when k₂ = 0.5. The maximum value of BCA no longer continues to increase with the increase of the anchorage length when k₁ ≥2.0, but the value range of k₂ expands, with which BCA has the maximum value. The calculated value of the derived BCA agrees better with the test one as compared with the model test results of tension-compression composite anchor. The uplift bearing capacity of tension-compression composite anchor can reach 2.0 times that of the tension type anchor under the same anchorage length. So the tension-compression composite anchor has a very good prospect in engineering application.