Self Drilling Hollow Rock Bolt VS Casing Pipe, Which Is Better to Support Unstable Conditions?

When supporting the slopes, foundations, and tunnels, we usually use self drilling hollow rock bolts or casing pipes. If the condition is loose, broken, which is better? I prefer the former. Why? Let’s see it.

What Is Self Drilling Hollow Rock Bolt?

There are six primary parts that construct a complete self drilling anchor rock bolt. They separately are a sacrificial drill bit, a fully threaded hollow steel bar, a coupler to continue the hollow steel bar if necessary, a plate and a nut to transmit the force from rock mass, a centralizer to ensure the hollow steel bar being at the central position of the drilling hole, and an alternative shank is required if the drilling rig has the percussion function.

Advantages of Self Drilling Hollow Rock Bolt

1. Hollow bolts are drill pipes, grouting pipes and bolts, no grouting pipes or exhaust pipes are required, and the construction equipment is simple;

2. The full-length bonding and anchoring is closely combined with the surrounding rock and soil, and the pulling force bearing capacity is larger;

3. The force value range of common bolts is 200kN-7940kN, and the selection range is wide;

4. The product can meet temporary or permanent support (galvanized);

5. There are many types of drill bits, which are suitable for a wide range of strata (sand soil-IV and V-level surrounding rocks);

6. Fewer personnel are required during construction, only three people are required, and the labor cost is low;

7. It can be used in special strata or strata with unknown geological conditions, and the effect of pore formation and force value is better than other bars;

8. The disturbance to the stratum during the construction process is small;

9. Grouting during drilling can properly expand the hole diameter and improve the bearing capacity of the drawing force;

10. The impact on the surrounding environment is small during drilling and construction, and almost no pollution is produced.

Construction Methods

Drilling first and then grouting:

Prepare the drilling rig, materials → install the bolt and drill bit → connect the bolt to the drilling rig, connect the compressed air or water pipe → drill → flush the hole → extend the bolt → drill → complete the drilling → connect the grouting pump → grouting → installation Backing plate, nut

Simultaneously drilling and grouting:

Prepare the drilling rig, materials → install the bolt and drill bit → connect the bolt to the drilling rig, grouting pump → drilling → flush the hole → extend the bolt → drilling → complete the drilling (grouting completed) → install the backing plate and nut

Usable Drilling Equipment

1. Down-the-hole drilling rigs and top-drive hydraulic rock drilling rigs

2. Anchor drilling rig rock drilling rig

3. Excavation and modification of drilling rig

4. Split drilling rig (electric and hydraulic)

5. Hand-held drilling rigs available below R32 specification

Drilling Speed in Different Rock

1. Silty clay---0.5min/m, the grouting pressure is 1MPa, the connection time is about 3min, and the water-cement ratio of the cement slurry is 0.5.

2. Round gravel, strongly weathered rock---1min/m, grouting pressure 0.3-0.5MPa, cement slurry water-cement ratio 0.5-0.55.

3. The surrounding rock of grade IV and grade V---0.5-1min/m, the grouting pressure is 0.4MPa, and the water-cement ratio of the cement slurry is 0.45.

4. Vc grade surrounding rock---shale 1min/m, mudstone 0.5min/m, grouting pressure 0.5-2.0MPa, cement slurry water-cement ratio 0.45.

Above all, I think the self drilling hollow rock bolt is a better way to support broken and loose conditions.

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