Anchoring mechanism and application of hydraulic expansion bolts(3)

3.4 Construction technology

(1) Drilling hole. The holes with the 38 mm diameter are drilled by the pneumatic drill according to the design angles of the bolts.

(2) Bolt installation. The pallets are installed on the rod bodies,and the rod bodies are sent to the bottom of the drill holes.

(3) Water injection. The water injection hole and the high pressure water-injection pump are combined with the water pipe. The water pressure should not be less than 20 MPa and the injection time should last longer than 5 min. This makes the rod body expand fully.

(4) Initial anchoring force. The value of initial anchoring force should be larger than 60 kN. The pallet should stick to floor rock tightly.

(5) Final work. The high pressure water-injection pump is shut down when the rod body is expanded fully, after which the pump and the water pipe are retracted.

3.5 Application effect

Deformation observation of the mining roadway is carried on when excavating (shown in Fig. 8). After the hydraulic expansion bolts are used to control floor heave for 20 days, the floor is gradually stable. The final convergence of the floor is about 95 mm. This means that the roadway can satisfy the operating requirement of the mine. Comparing with the mining roadway of N205 working face, which does not use the hydraulic expansion bolts to control floor heave, we found that the application effect on the floor heave control of the hydraulic expansion bolts was good. This not only reduces rebuilding quantities but also improves excavation speed of the roadways.

4.Conclusions
(1) The anchoring force of the hydraulic expansion bolt is expressed in four forms, namely support anchoring force,tension anchoring force, expansion anchoring force and tangent anchoring force. Expansion anchoring force is the unique anchoring force of the hydraulic expansion bolt.
(2) The mechanism of floor heave control using the hydraulic expansion bolts is revealed in two aspects. On one hand,the hydraulic expansion bolts can improve the strength of the floor rock to prevent the development of the plastic area. On the other hand, the hydraulic expansion bolts can provide circumfluence resistance to prevent the flow of the plastic area in the floor rock.
(3) The hydraulic expansion bolts can not only overcome the disadvantages that rock powder cannot be fully blasted out of drill holes which affects the floor heave controlling effect of resin bolt in soft rock roadways seriously but also provide powerful anchor force due to its full-size grouted anchor form.
(4) Engineering application shows that the hydraulic expansion bolt with the reasonable support parameters can control floor heave. This not only reduces rebuilding quantities but also improves excavation speed of the roadways.