Anchor quality is a critical factor influencing the anchoring performance after drilling and expanding anchor holes. Anchoring at the bottom of the hole is an effective technical measure to improve the anchoring quality of mudstone cemented soft rock tunnels. Through a comprehensive research approach including theoretical analysis, laboratory experiments, and numerical simulation, we conducted anchoring quality tests on a self-developed bottom-hole single-wing inverted wedge-shaped hole-expanding device. The anchoring quality under different hole-expanding parameters was analyzed to reveal the anchoring enhancement mechanism at the bottom of the anchor hole. We established an anchoring model for bottom-hole hole-expanding anchoring and derived the formula for the axial force on the anchor rod during hole-expanding anchoring. The experimental results show that when the anchoring agent is K2335 resin anchoring agent, the hole-expanding length is 100 mm, the hole-expanding diameter is 58 mm, and the inverted wedge angle is 9°, the anchoring effect is optimal with a solidification rate of 92.9%. Even after the anchor rod slips and loses anchor, it still maintains a high anchoring force. On-site application results indicate that inverted wedge-shaped hole-expanding anchoring can effectively increase the anchor rod support strength, reduce tunnel deformation, and ensure the stability of coal mine tunnels. This method has significant guiding significance for solving the anchor rod support of mudstone cemented soft rock tunnels.
Zhang et al. (Tue,) studied this question.