The mainline tunnel in this section is mainly shallow tunnel with large cross-section. The grade of the surrounding rock is form IV to V class. The geological condition is relatively poor. According to the project situation, the self drilling anchor bolt was chosen as the basic supporting equipment considering the convenient construction and low cost.
Self drilling anchor bolt system is mainly used for tunneling, slope stabilization, and foundation with micropiles. It’s also widely used in the railway system, metro project, etc. It can be installed in sites with weak rocks, loose soil, weathered layer, sand with stone layer and so difficult to create a hole in complex formation. The unconsolidated ground condition favor the self drilling anchor bolt technique for fast and simple method of installed compared to the traditional method.
In order to ensure the self drilling anchor bolt can play the important role, and guarantee construction safety, the following are the detailed rules of the advance anchor bolt construction technology.
The Φ25mm self drilling hollow anchor bolt should be adopted on the crown of the tunnel. The drilling machine will apply hydraulic descaling system drill rig or the pneumatic drill. After the self-manufactured rack has been prepared, try to drill one self drilling anchor bolt which is 3m long. When drilling, take attention to the adjustment of the water pressure. If there is no problem, drill the self drilling anchor bolt with the same angle. Make records at any time during the drilling process.
After the anchor bolt reached the designed depth, set the plug into the tail of the drill pipe. Then tighten the nut, block off the hole, and connect the rod end and grouting pipe with the quick coupling. The next step is grouting. Grouting the cement material with BW250 grouting mortar pump until reached the predetermined pressure. Finally, arrange the mudjack and anchorage to make the surrounding rock and rock bolt form an entirety as soon as possible.