高预紧力锚杆破断及其控制的宏观力学机制研究

Research on macro-mechanics mechanism of bolt fracturing and its control with high pre-tensioned force

针对高预紧力锚杆易破断问题,采用现场调研、理论分析方法,分析了破断锚杆断口与杆体形态和井下高预紧力锚杆受载类型及受力状态,研究了锚杆预紧力与预紧力矩的关系,建立了侧向扭转载荷、轴向拉伸载荷和横向剪切载荷复合作用下的锚杆受力模型,揭示了预紧力矩对锚杆横截面切应力及周边主应力的影响,结合第三强度理论分析了多种类型载荷复合作用下高预紧力锚杆破断的力学机制,并提出了控制高预紧力锚杆破断的力学机制与对策。研究结果表明:井下服役中的锚杆既可能承受较大的单一类型载荷,也可能承受多种类型载荷的复合作用;锚杆预紧力与预紧力矩呈正比,与螺母-托盘之间的摩擦系数呈反比;扭转、拉伸、弯曲复合作用下锚杆横截面周边最大主应力与预紧力矩呈正相关;承受扭转、拉伸、弯曲复合作用是高预紧力锚杆破断的主要原因,其中高预紧力矩影响着锚杆横截面周边主应力状态,并促使受力状态满足强度条件;从减少锚杆延伸量、避免岩层错动影响和降低预紧力矩等方面采取相应措施有助于控制高预紧力锚杆破断。

Aiming at the issue that highly pre-tightened bolts are prone to fracture,and adopting methods of field investigation and theoretical analysis,the morphology of fracture surfaces and bolt bodies of fractured bolts as well as the loaded types and forced states of highly pre-tightened bolts underground were analyzed.The relation between the pre-tensioned force and pre-tensioned torque of bolts was investigated,the stress model of bolts under the compound effect of lateral torsion load,axial tensile load and transverse shear load was built,the effect of pre-tensioned torque on the shear stress on bolt cross-sections and on the principal stress in the surrounding was revealed.The mechanics mechanism of fracturing of highly pre-tightened bolts under the compound effect of multiple types of loads was analyzed as combined with the third strength theory,and the mechanics mechanism and countermeasures to control the fracturing of highly pre-tightened bolts were proposed. The research results show as follows: the bolts working underground could not only bear large single-type load,but also bear the compound effect of multiple types of loads. The pre-tensioned force on bolts is proportional to the pre-tensioned torque,and is inversely proportional to the friction coefficient between the nut and tray the maximum principal stress in the surrounding of the crosssection of bolts that are under the compound effect of tension,torsion and bending is positively correlated with the pre-tensioned torque.Bearing the compound effect of torsion,tension and bending is the main reason for the fracturing of highly pre-tightened bolts,where the high pre-tensioned torque has a significant influence on the principal stress state in the surrounding of bolt cross-section and makes the stress state satisfy the strength condition. To take corresponding measures in the regards of reducing the extension of bolts,avoiding the influence of rock dislocation and decreasing the pre-tensioned torque is helpful in controlling the fracturing of highly pre-tensioned bolts.