Development of a Pre-Tightening Force Quantitative Exerting Device and Research on the Control Effect of Anchorage Parameters

To address the challenge of quantitatively exerting bolt pre-tightening force in roadway support and to clarify the control effect on surrounding rock under different combinations of anchorage length and pre-tightening force， a self-retracting pre-tightening force quantitative exerting device was developed， and four field comparative tests of different bolt anchorage length and pre-tightening force combinations were designed and carried out. The results showed that the device exhibited a deviation of less than 4% between the design and actual pre-tightening force values in laboratory tests and less than 10% in field tests， demonstrating that it met all operational requirements. The bolt stress evolution exhibited three distinct stages： a rapid increase， a slow increase， and a stabilization stage， which was basically consistent with the deformation behavior of the surrounding rock. Furthermore， the measured average values of the anchorage agent installation fell below the design values. The loss rate of the anchorage length increased with a higher deformation rate of the surrounding rock. This loss essentially ceased as the deformation tended to stabilize. When the anchorage length remained constant， doubling the pre-tightening force resulted in a reductions in surrounding rock deformation of 40% and 35% in the respective tests， demonstrating a significant control effect. When a pre-tension force of 60 kN was applied and the anchorage length was reduced by 0.4 meters， the deviation in surrounding rock deformation maintained within 16%. This confirmed that increasing the pre-tension force significantly enhanced surrounding rock stability. The experimental results indicated that a moderate reduction in anchorage length， under specific conditions， did not significantly affect the support effect of the surrounding rock， which is consistent with existing research conclusions.