Application of hollow grouting anchor bolt in tunnel pre-support engineering

Hollow grouting anchor bolt pre-support technology is a construction technology for auxiliary tunnel excavation under unfavorable geological conditions. The technology is highly pertinent, safe and reliable, and is mainly suitable for pre-reinforcement protection under unfavorable geological conditions such as severe weathering, weak surrounding rock, fault rupture zone and water-rich surrounding rock.

Grouting reinforcement is to drill hollow anchor bolts along the tunnel excavation contour line at a certain distance and angle. Hollow anchor bolt plays double function, advance support and grouting pipe. Grouting reinforcement is to use the pressure of grouting pump to make the slurry penetrate and diffuse into the formation porosity or fissure through the hollow bar. Grouting reinforcement can improve the self-stability of the excavation surface by improving the soil physical properties, so as to limit the relaxation and deformation of the ground.

Sijialing Tunnel is 840m in length and 160m in maximum buried depth. The geology in the tunnel is dominated by limestone and dolomite with good strength and stability. However, 60～150m section from tunnel exit passed through a trench, and the tunnel buried depth at the trench bottom is 5 ~ 15m. Sections with more than 8m buried depth in the trench, the surrounding rock has a fragmented structure with poor integrity and stability. Sections with less than 8m buried depth in the tunnel has poor conditions for hole formation. Due to the terrain restrictions, tunnel construction can only proceed from the side of starting point. When construction 690m reaches to weak geology, hollow anchor bolt grouting technology is used to pre-support and strengthen surrounding rock, which has achieved good results.

The application of hollow anchor bolt grouting technology in tunnel pre-support engineering provides a safe working environment for tunnel excavation. Especially for the tunnel with short supporting length, hollow anchor bolt not only ensure the grouting and supporting effect like small conduit, but also saves the small conduit processing time, which speed up the construction progress. Therefore, hollow anchor bolt grouting technology should be widely used and promoted in tunneling construction.