In the deep exploration of mining development, with the increasing depletion of shallow resources, deep mining has become the only way for industry development. However, the deep hard rock environment has brought unprecedented challenges to mining work, such as high ground stress, poor rock stability, and potential rock burst risks, which seriously threaten the safety of miners and mining efficiency. To meet these challenges, engineers are constantly exploring new support technologies. Expandable rock bolts are an innovative support method that has demonstrated great potential in providing support for deep hard rock tunnels due to their unique advantages. This paper will discuss the anchoring performance of expandable rock bolts in hard rock conditions, revealing their application potential.
Working principle of expandable rock bolts
Expandable rock bolts are a form of support that uses high-pressure water to expand the anchor to form a close fit with the rock mass. The rock bolt undergoes permanent plastic expansion deformation with the geometry of the anchor hole, making it firmly embedded in the surrounding rock and generating significant friction. In addition, when the rod expands, the rock bolt exerts a higher pressure on the surrounding rock mass, forcing the surrounding rock to produce strain and increase the stress of the surrounding rock. Relatively, the surrounding rock also produces corresponding extrusion stress on the rock bolt. In the process of water filling and expansion, the diameter of the hydraulic expansion anchor rod changes from thin to thick, and there is a certain amount of contraction in the longitudinal direction so that the tray of the rock bolt is tightly pressed against the surface of the surrounding rock, generating an upward supporting force, thereby achieving prestressing of the surrounding rock.
Anchorage performance in hard rock conditions
At a deep mining site, researchers conducted a comprehensive test on the anchoring performance of expandable rock bolts under hard rock conditions. Through pull-out tests and water pressure monitoring, it was determined that expandable rock bolts perform exceptionally well in hard rock.
Excellent pull-out performance
Test results show that the pull-out force of expandable rock bolts under hard rock conditions is generally higher than that of traditional split sets. The average pull-out force of the expandable rock bolt reaches 100.10kN, which is approximately 3.64 times that of the split set. This significant difference is mainly attributed to the fact that the expandable rock bolt can better adapt to the undulation of the borehole wall under the action of high water pressure and realize a close fit with the rock body, thus significantly increasing the contact stress and mechanical bite force with the anchoring borehole wall.
Stable and reliable working performance
Through long-term hydraulic pressure monitoring, it has been determined that the expandable rock bolt can maintain relatively stable water pressure under hard rock conditions, indicating its stable and reliable working condition. In addition, water pressure monitoring revealed the interaction between the rock bolts and the surrounding rock. When the surrounding rock of the tunnel is affected by mining stress and causes elastic deformation of the borehole, it will squeeze the rock bolt and increase the water pressure inside the rod. This change verifies the close fit between the rock bolt and the surrounding rock and provides a reference for monitoring changes in mining stress.
Future development direction
Expandable rock bolts have shown excellent anchoring performance under hard rock conditions and have broad application prospects. However, to further promote its application in actual engineering, the following problems need to be solved:
- Dynamic load resistance: although expandable rock bolts perform well under static load conditions, their ability to resist dynamic loads such as rock bursts needs to be further verified. In the future, we can evaluate their work performance by conducting simulation rock bursts and other test methods.
- Shear resistance: some expandable rock bolts may fail under high-pressure water, so it is necessary to research shear resistance and optimize rock bolt design.
- Corrosion resistance: in harsh environments such as humidity and high salt, expandable rock bolts are prone to corrosion, affecting their service life and anchoring effect. Expandable rock bolts should be developed with corrosion-resistant materials, and anti-corrosion measures should be taken when installing downhole.
Conclusion
Expandable rock bolts are a new type of support that has great potential to reinforce deep hard rock tunneling. Its excellent anchoring performance, stable and reliable working state, and convenient installation method provide a new solution for surrounding rock control in deep mining. With the continuous advancement and improvement of deep mining technology, expandable rock bolts are expected to be used in more complex geological conditions, contributing greater strength to the safety and efficiency of mining development.
