DOI: 10.3390/pr12010113 ISSN: 2227-9717

Analysis of the Support Failure Mechanism Caused by Bolt Pre-Tightening Force Loss

Xin Sun, Jingyi Cheng, Zhijun Wan, Jiakun Lv, Kechen Liu, Kuidong Gao
  • Process Chemistry and Technology
  • Chemical Engineering (miscellaneous)
  • Bioengineering

The pre-tightening force loss (PTFL) of bolts is an important but underestimated cause of roadway instability. In mine anchorage systems, the actual pre-tightening force of bolts is only 50% to 80% of the design value. Through a case study at Xiahuo Coal Mine, it was found that the essential causes of PTFL are the increasing friction coefficient between supporting units controlled by factors such as pre-tightening torque levels, pre-tightening cycles, and surrounding rock roughness. This study investigates the behavioral characteristics of PTFL and its influence on surrounding rock failure in roadways. This research reveals a linear correlation between pre-tightening force and torque, with an average torque conversion coefficient of approximately 0.19. However, the PTFL increases with higher levels of pre-tightening torque, increasing pre-tightening cycles, and rougher surrounding rock conditions. For every 30 N·m increase in pre-tightening torque, the PTFL increases by approximately 1.67 kN. Reducing the PTFL can expedite the stress redistribution process and shorten the self-stabilizing period of the roadway by approximately 10 days, thereby enhancing the active supporting potential of bolts.

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