Strictly prohibited operations when using mine support bolts

Mine support bolts are a crucial aspect of coal mining, playing a vital role in supporting the mine body. Therefore, understanding the characteristics of support bolts and their usage methods is essential. This is a prerequisite for maximizing the support effect and ensuring mine stability, and understanding some usage precautions can prevent accidents.

Operational steps for mine support bolts:

(1)The tail of the mine support bolt is the most complex part of the entire bolt body in terms of stress and is prone to damage. Stress analysis of the threaded section of the support bolt shows that the change in diameter causes stress concentration of 2-3 times in the threaded section; due to unreasonable spherical rotation between the tray and the spherical pad, self-locking occurs between the two spherical surfaces, causing the stress on the support bolt to deteriorate sharply or even fracture.

(2)When the installation angle of the mine support bolt is too large and the tensile stress reaches a certain value, long-term loading will cause bending and cracking, or even fracture, of the threaded section at the tail of the support bolt; when the applied pre-tightening torque is greater than 600 N·m, the combined stress on the support bolt approaches the yield stress of the material, and the support bolt will first crack at the bending point, and then the crack will expand, causing the support bolt to fracture before reaching the breaking tensile force.

(3)Combined tensile-bending-torsional, tensile-shear-torsional, and tensile-bending-shear-torsional actions are common stress states during the installation of underground support bolts. The closer to the fixed end, the greater the stress, so the unfavorable position is the fixed end.

(4)Optimization schemes such as vertical installation of support bolts, redesign of centering spherical pads, full-length anchoring of support bolt pre-stress, and adjustment of support bolt pre-tightening torque to 400 N·m, etc., can reduce the impact of harmful stress on the bolt body.