Study On Failure Mechanism Of Anchorage Segment Of Pull-twist Coupling Anchor Cable Under Pull-out Loads

Anchor cable anchoring technology can effectively control the deformation and improve the stability of engineering rock and soil mass,which has many advantages such as active support,security and economy so that anchor cable as the main support unit is widely applied in the slope engineering,tunnel engineering and mining engineering in the world.Because of the structural characteristics of the anchor cable,it will produce reverse rotation which affect the anchoring capacity of the anchor cable when it is pulled.In this paper,the failure mechanism of anchorage segment of pull-twist coupling anchor cable under pull-out loads is revealed by means of laboratory pull-out test,theoretical analysis,numerical simulation and risk analysis.The main research results are as follows:(1)By using the self-developed pull-twist coupling system of the anchor cable,the pull-out tests for anchor cables with non-rotation and free rotation conditions were carried out.It is found that the axial tension of the anchor cable with non-rotation is larger than that in the free rotation state,and the torque reverse force produced by cable pulling weakens the axial tension.The axial tension and torque of the anchor cable significantly increased with the increase of the confining pressure.The strain of the anchorage segment of the anchor cable is in accordance with the exponential function relationship along the axial direction,and increases with the power function relation of the pull-out displacement.(2)The load–displacement curve of the pull-twist decoupling about anchorage system is analyzed by using piecewise function,and the cable pull-twist coupling model is constructed.The axial tension–displacement relationship,torque–displacement relationship and torque–axial tension relationship are obtained,and the coupling effect between axial tension and torque of anchor cable is revealed.(3)The numerical calculation model of pull-twist coupling in anchorage segment of anchor cable is established to verify the rationality of the coupling model.The failure evolution process and torsional response of the anchorage system under the effect of pull-twist coupling are obtained by the characteristics of each representative unit of the anchorage system under the coupling effect of axial tension and torsion.The law of stress and strain variation of anchorage unit in anchorage system is revealed.(4)The hierarchical structure model is established by using analytic hierarchy process(AHP),and the failure risk of anchor cable anchorage system is analyzed.Based on the weight calculation and index quantification of the failure factors of the anchorage system,the failure risk level of the anchorage system is evaluated,and the countermeasures are proposed for the risk treatment level and scope of the anchorage system.All these above mentioned were to provide theoretical basis for the pull-out force analysis and design of anchor cable anchorage segment,and provide a reference for similar engineering practice.