4 Methods of Tunnel Support, the Introduction of Rock Bolts in Tunnel

There are four types of support commonly used in tunnels: shotcrete support, rock bolts support, metal mesh support, and steel arch support.

Shotcrete support is to mix cement, sand, stone, water and other materials needed in a certain proportion. After mixing evenly, spray them to the position where they need to be sprayed through the nozzle. The construction of this method is simple. It is convenient and can quickly condense the sprayed place in a short time, effectively consolidating and waterproofing the tunnel. It is an indispensable and important support method in construction.

shotcrete support method in tunnel - rock bolts in tunnel - Sinorock

A metal mesh is a mesh made of metal materials. It should be used in combination with other support types. If only metal mesh is used for support, it is neither safe nor stable. Before erecting the metal mesh, a layer of concrete should be sprayed on the rock to strengthen the stability of the metal mesh.

The steel arch is a ring-shaped steel used for support in the tunnel. There are mainly steel types such as I-beam and grille arches. During the tunnel construction, jetting, poles, and nets were installed in places with particularly poor rock formations.

Rock bolt support is a reinforcement support method used in tunnel construction. This support method is simple and clear, can reduce the use of materials and improve the construction speed. 

Self-drilling rock bolt construction technology is a new type of anchoring technology developed in recent years, which is suitable for various complex geological conditions and construction site environments. The self-drilling bolt construction realizes the integration of drilling, grouting and anchoring functions. The construction process is simple, the construction efficiency is high, the anchoring effect is good, and there is no need to worry about the problem of hole collapse. It is widely used in tunnel support projects.

Components of Rock Bolts in Tunnel

The self-drilling rock bolt consists of six parts, the hollow anchor bar, the drill bit (sacrificial), the coupler, the backing plate, the nut and the centralizer. The hollow anchor bar is made of high-tensile alloy steel seamless steel pipe, and the ultimate load and yield load can meet various complex geological conditions according to the design requirements. We need choose different models of rock bolt according to the rock and soil conditions, such as " Hardened Button Drill Bit (ES-F) ", " Hardened Cross-cut Drill Bit (EX) " and so on. According to the processing technology, it is divided into all-steel drill bits and alloy drill bits; the coupler is a rod body extension part, which is suitable for hollow bolt anchor. It reaches the same strength, and the two rod bodies can be seamlessly connected through the coupler, and there will be no leakage during grouting; the nut and the backing plate are used together, and the nut first transmits the anchoring force of the hollow bolt to the backing plate, The backing plate then applies the anchoring force to the surrounding rock, transmits the stress, improves the end force, and enhances the anchoring effect of the self-drilling bolt; the centering device can ensure that the self-drilling bolt is always in the center of the hole during the construction process. position, so as to ensure that the thickness of the slurry around the rod body is uniform, and further strengthen the anchoring effect.


Compared with ordinary bolts, rock bolts in tunnel have the following advantages:

1. Rock bolts in tunnel are suitable for all kinds of rock and soil conditions. Especially in the geological conditions where the ordinary bolt construction technology is not easy to construct, the effect is better, such as the geology of easy-to-collapse holes;

2. The drilling depth is not limited. Due to the limitation of existing bolt materials and drilling equipment, the drilling depth of conventional bolts is relatively shallow, but the drilling depth of rock bolts in tunnel can be relatively large due to the low drilling resistance, the current drilling depth that self-drilling bolts can reach is 18m;

3. Rock bolts in tunnel are suitable for construction in narrow space. The length of a single rod body of self-drilling bolt can be cut or extended as required, and the common specifications are 2m, 3m, 4m and 6m;

4. The technological process is simple. Rock bolts in tunnel complete drilling, grouting and anchoring in one drilling, simplifying the technological process and speeding up the construction speed;

5. Rock bolts in tunnel are beneficial to stabilize the hole wall. At the same time of drilling, a screw grouting machine is used to pressurize and supply cement slurry with a water-cement ratio of 0.4~0.5, so that the slurry can quickly fill the hole and the cracks in the rock and soil mass and be absorbed and solidified by the hole wall to ensure the stability of the hole wall.

6. Better anti-corrosion performance. If the rock formation contains groundwater, the rock bolts in tunnel will be badly corroded by the environment so that the years of use will be reduced significantly. Fortunately, every rock bolt in tunnel from Sinorock will be embalmed, either hot-dip galvanized or epoxy coated, or both. So they can be used for permanent support in tunnel.

The construction process of the rock bolts in tunnel is as follows:

1. Preparation before construction: Check whether the functions of the drilling rig are normal, whether the drill bit and the rod body are damaged, and whether the rod body is unblocked, etc. After ensuring that there is no problem, screw the hollow bolt body to be used with the drill bit;

2. Drilling and grouting: connect the rod body and the grouting pipe to the drilling rig through a rotary grouting adapter, and perform grouting during the drilling process to achieve the simultaneous completion of drilling and grouting;

3. The length of the bolt body: if the length of a single self-drilling bolt cannot reach the designed drilling depth, the length of the connecting sleeve can be used to meet the design requirements;

4. Install the backing plate and nut: After the grouting is completed, install the backing plate and the nut in sequence on the exposed part of the self-drilling rock bolt outside the rock body close to the construction surface to ensure the anchoring effect.

The above is the introduction of 4 methods of tunnel support, especially for rock bolts in tunnel. If you have any questions of need our products, please contact us at sinorock@sinorockco.com. We will response in 24 hours.

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