Analysis for bearing characteristics and reinforcement effect of counter-pulled bolts and cables

With the increase of mining intensity, the spatial relationship between roadways becomes more and more complex, and the counter-pulled bolts and cables are used in the roadway support of coal mine.The existing research on bolts and cables is basically directed to the traditional anchoring bolts and cables, and there is little study on the counter-pulled bolts and cables.Therefore, the bearing characteristics and reinforcement effects of counter-pulled bolts and cables are not fully understood.To investigate the bearing characteristics and reinforce-ment effects of counter-pulled bolts and cables, the simulation method of counter-pulled bolts and cables based on FLAC^3D software was proposed and verified.The problem that the pile structure element in FLAC^3D cannot be preloaded is solved in the proposed method.Numerical models for the tension and shear of counter-pulled bolts and cables were established to analyze the axial and tangential bearing characteristics of counter-pulled bolts and cables, and the shear resistances between counter-pulled bolts and cables were compared.Numerical experiment for the counter-pulled bolts and cables preventing the shear sliding of discontinuity was conducted to investigate the reinforcement effect of counter-pulled bolts and cables on the shear sliding of discontinuity under in-situ stress.Numerical experiment for the counter-pulled bolts and cables preventing tension rupture of discontinuities was conducted to investigate the reinforcement effect of counter-pulled bolts and cables on the tension rupture of dis-continuities under in-situ stress.Based on the results, the applicability of counter-pulled bolts and cables was ana-lyzed.The results show that:① the proposed simulation method can exactly simulate the structures and the axial and tangential bearing effects of counter-pulled bolts and cables; ② compared with none-encapsulated counter-pulled bolts and cables, the fully-encapsulated counter-pulled bolts and cables are more sensitive to tensile deformation with faster resistance increase and wider supporting range, but are also easier to be broken in the middle of the bodies; ③ the shear resistance of fully-encapsulated counter-pulled bolts and cables is larger than that of none-encapsulated counter-pulled bolts and cables.When the shear displacement is small, the shear resistance of the counter-pulled bolt is larger than that of the counter-pulled cable.With the increase of the shear displacement, the shear resistance of the counter-pulled cable increases gradually and is finally larger than that of the counter-pulled bolt; ④ under in-situ stress, the counter-pulled bolts and cables can effectively prevent the tension rupture of discontinuities by mainly exerting axial bearing capability, but their control effect on preventing the shear-sliding rupture of discontinuities is poor; ⑤ in the reinforcement of jointed rock mass, the axial forces of the fully-encapsulated counter-pulled bolts and cables are distributed as “high in the middle and low on both sides”.The bolts and cables are easy to be broken in the positions of discontinuities, so that special attention should be paid for improving the strength of the bolts and cables.