剪切过程中锚杆的轴向和横向作用分析

为了分析锚杆轴向力和横向剪切力分别换算的结构面抗剪强度大小规律,依据最小势能原理的变分法,并考虑结构面剪胀特性,建立加锚结构面抗剪强度计算公式。通过加锚结构面直剪试验验证理论计算的有效性,结合理论计算公式,分析了在不同锚杆倾角下围岩强度、锚杆直径和法向应力对锚杆轴向力和横向剪切力换算的抗剪强度影响规律,以及预应力对抗剪强度的影响。结果表明:加锚结构面抗剪强度计算结果与试验结果吻合较好;当锚杆倾角逐渐增大时,锚杆轴向力发挥的抗剪强度逐渐降低,横向剪切力发挥抗剪效能逐渐增大,当锚杆倾角为120°~150°时,轴向力换算的抗剪强度基本为0,而横向剪切力换算的抗剪强度最大;随着围岩强度或法向应力的增大,锚杆轴向力换算的结构面抗剪强度减小,但随锚杆直径或预应力的增大,锚杆轴向力换算的结构面抗剪强度增大;当围岩强度和锚杆直径增大,锚杆横向剪切力换算的抗剪强度会明显增大,而预应力增大会使锚杆横向剪切力换算的抗剪强度呈现降低趋势。

Analysis of axial and transverse effects of rock bolt during shearing process

This paper analyzes the shear strength of the bolted rock joint contributed by the axial force and transverse shear force. The formula of the shear strength of a bolted joint with dilatancy is derived using the variational principle of minimum potential energy. The theoretical solutions are verified with the direct shear test of bolted structure. Then the shear strength of the bolted structure is contributed by the axial force and transverse shear force. It is analyzed with different rock mass strengths, bolt diameters, normal stresses and pre-stresses, using this theoretical method. All the relevant analyses show that the computed results agree well with the results of experiment. The shear strength of the jointed structure contributed by the transverse shear force is remarkable. When the bolt inclination increases gradually, the joint shear resistances contributed by the transverse shear force and the axial force increases and decreases respectively. When the bolt inclination is 120°－150°, the joint shear resistance contributed by the axial force is almost zero. The joint shear resistance contributed by the axial force decreases as the rock mass strength and normal stress increase. It increases obviously as the bolt diameter and pre-stress increase. The joint shear strength contributed by the transverse shear force increases as the rock mass strength and bolt diameter increase, but decreases slightly as the pre-stress increases.