A self-drilling rock bolt is a kind of hollow bolt, which doubles as a drill pipe and a grouting pipe. The slurry is sprayed from the drill bit through the hollow of the bolt to fill the cracks and holes in the stratum around the bolt so that the rock bolt can be connected with the surrounding soil. The solidification becomes a whole and plays the role of reinforcement, so it can be called a new support technology that integrates the three functions of drilling, grouting, and anchoring.
The self-drilling rock bolt has the characteristics of adding and extending, so the rod body is shorter and a smaller drilling rig can be used. It is suitable for construction in basements, bridge bottoms, riversides, and narrow environments. It has been widely used in tunnels, mines, slopes, and other projects. Because it does not need a casing pipe, it is suitable for the treatment of diseases such as formations with easily collapsed holes, reinforcement of existing structures, and grouting to fill cracks.
Generally, the soil can be drilled with a pneumatic rock drill, and the bolts of the drilling rig are connected by a special shank coupling. This rock drill only uses pneumatic support because there is no guide rail for propulsion, and its stability is poor. If it is used for hard rock layers or long bolts, a propelling rig with guide rails can be selected.
Self-drilling rock bolt consists of six parts: drill rod (anchor rod), drill bit, coupler, backing plate, nut, and centering device. The drill bit can be cast from wear-resistant alloy steel, and the slurry outlet hole is reserved. Different forms can be selected according to the conditions of the rock formation, such as "one" type, "cross" type, "cone" type, and other types; the anchor rod is made of high tensile strength alloy steel seamless steel pipe, and its specifications are R25, R32, R38, R51, T30, T40, T52, T76, etc.; the coupler, the backing plate, and the nut are all cast from alloy steel made.
The interior of the self-drilling rock anchor is hollow, and after drilling into the formation, pressure grouting can be carried out through the hollow channel. The slurry passes through the slurry hole of the drill bit, fills the hole from the inside to the outside from the bottom of the hole, and penetrates into the fracture of the rock formation. After the slurry solidifies, it will form an anchor together with the bolt and the surrounding rock mass. At the same time, the exposed end of the self-drilling rock anchor will be fitted with a backing plate and a nut against the rock surface. When the rock mass is deformed, pressure will be generated on the backing plate, and the backing plate and the nut will transmit the pressure to the bolt and anchor, so as to achieve the purpose of stabilizing the surrounding rock.
The drilling rig required for self-drilling rock bolts is mainly selected according to the stratum and terrain conditions of the construction. Because there are many types of drilling rigs, the principles of construction convenience and safety should be used. The grout used for the bolts is generally cement mortar (the water-cement ratio is 0.45~0.6, and the cement is 42.5 grade ordinary Portland cement.).
The self-drilling rock anchor can also be prestressed, and the length of the anchoring section and the free section is determined by calculation. The free section is generally completed with a jacketed PVC plastic pipe. Slope protection should be determined according to the soil conditions. Some use a spray anchor net to close the slope (weathered rock layer), some use concrete spraying in the middle of frame slope protection, and there are slope protection methods such as vegetation (soil slope) in the middle of frame slope protection.
The length of the self-drilling rock bolt is generally determined by the failure and pullout force test according to the soil conditions of the stratum.
Self-drilling rock bolts can be used to repair building foundations, reinforce road and railway slopes, and provide advanced support before tunnel excavation. With its efficient construction efficiency and simple construction method, the self-drilling rock bolt has gradually become the most effective way to support unstable conditions.
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