As for tunnels with developed bedding joint and plenty water burst, surrounding rocks belong to IV-V class, which is loose blocky structure and easy to break. If efficient methods don’t be adopted, it will influence project’s progress and quality, even cause security problems.
Because of broken, loose surrounding rocks, mixture of mud, worse stability after water seepage saturation, advanced support should be carried out to guarantee project. Mortar anchor bolt and ductule are difficult to drill holes, grout, control mortar’s plumpness and easy to collapse, time-waste and energy-waste. They provide channels for underground water’s invasion, which causes corrosion of steely rods and then influences anchor bolt’s durability.
While self-drilling hollow anchor bar can overcome above disadvantages. As advanced support, it can improve construction quality and progress effectively. In IV-V class surrounding rocks, self drilling anchor bolt can drill to designed depth and then grout. When grouting, non choking first and then stopping plug until slurry return to orifice. Slurry, as veins, permeates into broken rock mass under grouting pressure, ejects air and moisture, solidifies loose rocks and bonds anchor bolt with surrounding rocks, which will enhance surrounding rocks’ integrity, anti-permeability and stability, and help to excavate and support project.
This supporting principle mainly depends on the combination of drilling, grouting and anchoring. It ensures grouting full, protects rocks’ inherent strength, prevents looseness and deformation and then reaches the goal of stabilizing surrounding rocks.
It is proved that adopting self drilling anchor bolt is not only quick, high-efficiency, but also safe and reliable. Its pulling resistance is more than designed. The cracks among rocks are filled closely and efficiency is good.
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