ZHANG Xiaojun, LIU Xiao
Journal of Railway Engineering Society. 2025, 42(3): 1-5.
Research purposes: Bolt anchoring is an important method for the prevention and control of engineering rock masses, especially in deep engineering. Its research has significant theoretical and practical implications. In view of the deficiencies in the research on the pre-tension of bolts in hard rock, gabbro anchor body specimens with different anchoring lengths were prepared, a bolt pre-tension monitoring system was developed, bolt pre-tension relaxation tests and uniaxial compression tests with different anchoring lengths were carried out, a pre-tension relaxation model was established, and the pre-tension contribution degree was defined.
Research conclusions: (1) As the anchoring length increases, the degree of pre-tension attenuation and loss is lower, and the effect of the pre-tension support control is more obvious. By monitoring the pre-tension, the anchoring quality can be analyzed and judged. The poorer the anchoring quality, the faster the pre-tension relaxes and the greater the relaxation amount. (2) In the elastic stage, the bolt pre-tension changes in a nearly linearly positive correlation with the applied load. The bolt pre-tension relaxes synchronously with the vertical stress. The processes such as the loading and relaxation of the surrounding rock in engineering can be reflected in real time by monitoring the pre-tension. (3) For the pre-peak load under uniaxial loading, as the load increases, the pre-tension of the fully grouted bolt undergoes stages such as slow increase, accelerated growth, and sudden increase. The accelerated growth and sudden increase of the pre-tension of the pre-peak load are directly related to the evolution of the damage and fracture of the surrounding rock of the anchor body. By monitoring the pre-tension, the internal evolution process of the anchor body and the surrounding rock can be grasped. (4) The post-peak load under uniaxial loading shows a process from gradual decline to sudden drop, and the pre-tension shows a process from continuous increase to sudden increase and then sudden drop. The change of the pre-tension is directly related to the evolution of the damage and fracture of the surrounding rock of the anchor body. By continuously monitoring the pre-tension, the rock mass failure and the occurrence of dynamic disasters can be predicted. (5) The pre-tension relaxation model has a good fitting effect and only requires two fitting parameters. The relaxation characteristics of the pre-tension can be well reflected and the relaxation process can be predicted through the quasi-viscous coefficient or the order value. (6) The lower the maximum contribution degree value at the time of failure, the worse the anchoring effect, and vice versa. The contribution degree can comprehensively reflect the anchoring quality, the contribution degree, and the working state. (7) The research results have guiding and reference significance for the anchoring mechanism, monitoring, prediction, and the mechanism, prevention and control of rock bursts of prestressed bolts.