The application of self-propelled rock bolt in loose accumulation body tunnel construction

Abstract: introduce a tunnel project which applied self-advancing rock bolts in the pilot support and shotcrete anchorage.

Overview

The tunnel is located in northern Pakistan Kashmir region, in the Pamirs hinterland. The landforms are mainly mountain valleys.

In the construction of tunnel project, the geology of No.2 tunnel entrance is very special.

The tunnel segment is 11m long, the thickness of the crushed rock is large and the whole rock body is loose. Groundwater is not developed, mainly are bedrock fissure water and water amount is poor. The stability of surrounding rock is very poor, big collapse and roof fall are easily happened.

This kind of geology mainly consists of stone, gravel, accumulated soil, and quicksand. Disturbance should be reduced while excavation. Local blasting and mechanical excavation method are designed for the tunnel construction. And support construction should be done immediately after excavation.

In the method of NATM, the initial support is bolted, reinforced mesh and shotcrete combined for the shotcrete supporting. However, drilling is difficult in this kind of geology. The traditional full-length bonded anchor bolt and advanced small catheter can’t be applied.

To solve the problem, IBO self-drilling rock bolts were used instead of small grouting pipes and hollow grouting anchors.

 Principle of self-propelled anchor rod construction technology

The self-drilling anchor combines the function of drill pipe with the hollow grouting anchor. The anchor rod body is hollow and equipped with grouting joints. The drilling and grouting reinforcement can be operated in the same step. At the same time, the continuous thread on the rod surface strengthens the bond resistance of the anchor itself.

Construction technology of self-drilling anchor and process

1. Preparation

According to the size of the tunnel to choose mechanical equipment and materials. The following is the introduction of self-drilling anchor on behalf of the small advance grouting pipe for advanced support.

• Machinery

Drilling rigs: self-propelled anchor can be installed by hand-held pneumatic rock hammer drill. Hydraulic drilling vehicle is also available. Select according to the project and construction requires.

Grouting equipment: electric mixer x 1, double liquid grouting machine x 1, grouting joints and grouting pipes, etc.

• Main materials

Φ32 self-propelled anchor rock bolts, cement, sodium silicate, accelerating agent, water, etc.

2. Construction

• Drilling

Assembling self-propelled anchor system first. Install the alloy drill bit at the end of the bolt. Measure and loft before drilling. Set the hole along the 40 cm outer ring. The drilling is performed at an angle of 10 ° after the lifting is completed.

Remove the rock drill when drilling to the tail 10 cm. install the stopper and anchor plate, and lock with bolt nuts.

Start the next cycle of drilling operation until reach the designed depth.

• Grouting

When drilling is completed, tighten the grout joint at the end of the anchor and begin grouting. The grouting material is cement. 1:1 cement-water ratio. 0.5-1.0 Mpa grouting pressure. If the groundwater is too much, cement slurry with water glass is used. Grouting with double liquid grouting machine.

Below is the process flow for self-drilling anchor bolting.

Features of self-drilling anchor bolt

1. Multifunction

IBO Self-drilling anchor bolt combines drilling, grouting and anchoring functions. It achieves the dual role of curing the surrounding rock and anchorage.

2. Speed and cost-effectiveness

The construction method of self-drilling anchor is simple and quick. The requirements for machinery and personnel are lower. One-time drilling & grouting can greatly shorten the operation time. It can play the role of rapid support for unstable rock strata.

3. Safety and good adaptability

The self-propelled anchor bolt is combined with the surrounding rock as a permanent support and to form a cured shell. It can greatly improve the construction safety.

Application of self-drilling anchor bolt IBO

Applicable to all kinds of loose, unstable geological sites.

Tunneling, slope stabilization, mining, micropile hollow bar and soil nail, etc.