Anchoring method utilizing self-drilling and self-anchoring extendable anchor rod applicable to soft and weak coal rocks

An anchoring method utilizing the self-drilling and self-anchoring extendable anchor rod applicable to soft and weak coal rocks, which comprises a simple drill bit, a combined rod body, and a tightening device;

• the head end of the combined rod body is connected to the simple drill bit via female threads in the drill bit, the combined rod body comprises a plurality of intermediate rod bodies, a plurality of connecting sleeves, and a tail rod body, wherein, the plurality of intermediate rod bodies are connected together via the plurality of connecting sleeves, the tail end of the last intermediate rod body is connected to the tail rod body via a connecting sleeve, the tightening device is connected to the tail rod body through a threaded connection, and the tightening device comprises a tapered rubber plug, a tray and a nut arranged on the tail rod body sequentially, said method comprising the following steps:
• a. using an ordinary drill rod to drill a hole at a designed position to ¼˜¾ designed hole length, and withdrawing the drill rod;
• at this point, the hole may collapse partially;
• b. selecting required quantity of intermediate rod bodies and connecting sleeves according to the designed hole length, utilizing the connecting sleeves to assemble the intermediate rod bodies and the tail rod body together to form an anchor rod body;
• mounting a simple drill bit to the front end of the first intermediate rod body, inserting the head end of the rod body into the hole, mounting the rear end of the rod body to a drilling apparatus and then drilling, extending the rod body utilizing the connecting sleeves and intermediate rod bodies in the drilling process, and extending the rod body with the tail rod body in the last extension, mounting the tail end of the newly combined rod body to the drilling apparatus and drilling after each extension, till the hole is drilled to its entire length;
• since the anchor rod body formed by the intermediate rod bodies and the connecting sleeves has ordinary screw-thread steel threads on its surface, which does not have a dust discharge function;
• therefore, no coal dust or rock dust is discharged in the drilling process, and a great deal of coal and rock dust exists between the self-drilling section and the rod body of the anchor rod for drilling hole;
• thus, end anchoring force is generated at the end of the rod body owing to friction, and, in the shallow ¼˜¾ section of the hole, since the hole drilled out in soft and weak coal rock mass collapses, shrinks and deforms quickly, the rod body is pressed to generate anchoring force;
• c. shutting down the drilling apparatus when the exposed length of the tail rod body is 30˜150 mm, separating the drilling apparatus from the tail rod body, fitting the tapered rubber plug and the tray over the tightening threads on the tail end of the tail rod body sequentially, and tightening up the nut for pre-tightening, so that the self-drilling and self-anchoring extendable anchor rod squeezes the coal mass and is embedded in the coal mass, and thereby the friction force between the self-drilling and self-anchoring extendable anchor rod and the coal mass is increased;
• thus, a primary installation is finished;
• d. at 1˜2 h after construction, the hole collapse, shrinkage and deformation are developed more fully and the anchoring force is higher;
• then, tightening up the nut with a wrench for secondary pre-tightening;
• such tightening can also prevent prestress relaxation of the self-drilling and self-anchoring extendable anchor rod incurred by construction of other self-drilling and self-anchoring extendable anchor rods nearby;
• e. at 12˜24 h after construction, underground worker checking the pre-tightening force on the self-drilling and self-anchoring extendable anchor rod with a torque-indicating wrench, and pre-tightening up the self-drilling and self-anchoring extendable anchor rod again if the pre-tightening force does not meet the requirement, so as to maintain the pre-tightening force;