How to Use Self Drilling Rock Bolts in Tunnel and Mining Constructions?

In constructions of excavating, such as tunnels, mining, and other underground projects, we have to support the soil and rock mass to ensure the people and equipment safe. Generally, we use rock bolts to do this. Rock bolt has a long history being used in tunnels and mines and now it is the turn of self drilling rock bolts. Today, Sinorock will introduce you how to used self drilling rock bolts in tunnels and mining constructions.

Factors Affecting Rock Mass Stability

rock mass condition in tunnel sinorock


The influence of lithology on rock mass stability includes two aspects. One is the influence of the physical and chemical properties of the rock on the stability of the rock mass, including the hardness of the rock and soil, weathering resistance, softening resistance, strength, composition, and water permeability. The influence of rock mass stability is reflected in the degree of development of joints and fissures and their distribution, the cementation of structural planes, the distribution of weak planes and fracture zones, etc.


Rock mass structure includes two aspects, structural plane and structural body. Structural planes refer to the differentiation planes and discontinuous planes of rock materials, planes, fractures, layers, bands and various geological interfaces with certain direction, scale, shape and characteristics. The structure is composed of various structural surfaces of different occurrences, and the rock mass is cut into unit blocks. The rock mass structural factors that affect the stability of rock mass mainly include the inclination, dip angle and strike of the structural plane, the number and continuity of the structural plane and so on.

Surface water

The impact of surface water on the rock mass is small, because the rock mass has high strength and is not easily eroded. However, if the rock is severely weathered and the rainfall intensity is high, the influence of surface water on the stability of the rock mass cannot be underestimated.

Types of Rock Bolts in Tunnel

Friction Bolts

It is a rock bolt that pushes a thin-walled steel pipe with longitudinal slits into a hole smaller than its outer diameter, and uses the steel pipe to generate resistance to the radial pressure of the hole wall.

friction rock bolt sinorock

Swelling Rock Bolts

The special-shaped cavity rod processed with thin-walled steel pipe is sent into a hole slightly larger than it, and by injecting water into the cavity of the rod at high pressure, the rod expands and generates frictional resistance on the hole wall to play an anchoring role.

Pre-stressed Rock Anchors

This type of rock anchors can provide a pre-stress to prevent rock mass deformation. Through the anchoring force generated by the anchor head, a certain pre-compression stress of the rock anchor is applied to the surrounding rock to actively strengthen the rock mass.

Self Drilling Rock Bolts

Self drilling rock bolt is a most widely used anchoring tools in geological constructions. It combines the drilling, grouting, and anchoring in one process. It is suitable for broken rock and conditions which are difficult to drill holes. What’s more, casing pipe is omitted in construction, which greatly improves the construction efficiency.

sinorock self drilling rock bolts

The most important parts of a self drilling rock bolt are the drill bit and thread hollow bar. The drill bits are various, including EX, EY, ES-F, EXX, EYY, ESS-F, and clay bit. You can select the precise one to improve the drilling efficiency most. There are two types of thread hollow bar, r and t thread. R thread hollow bar complies with international standard ISO 10208, so it is suitable for most drilling rig. T thread is customized, and Sinorock can also provide shanks adapter to match the drilling rig.

How to Use Self Drilling Rock Bolt in Tunnels and Mining?


In tunnels and mining, self drilling rock bolt is mainly used for initial support of tunneling. High pressure grouting is achieved through the hollow bar to strengthen the soil or rock mass to ensure the surface stability. According to the types of support in the tunnels and mining, it can be divided into fore piling, radial support, tunnel-face support, locking the foot support and reinforcement of the tunnel portal.

sinorock self drilling rock bolts in tunnel and mining

Construction Procedure

First, we should do some preparation, such as getting the drilling rig and rock bolts ready, prepare grout. Before drilling, we need to connect the drill bit with the hollow bar and check if the inner path is blocked. Also, we need to connect the grouting pipe with hollow bar. Then, start the drilling rig and the grout machine, drill and grout simultaneously. After the grout solidified, install the plate and nut.


A key reason why we use self drilling rock bolt in tunnels and mining is that the thread hollow bar can be cut at any position, or lengthened by couplers. Therefore, it is very convenient to support the rock mass in relatively narrow spaces where large equipment cannot enter.

We now know how to use self drilling rock bolts in tunnels and mining. If you need the products, please do not hesitate to contact us at, we will response to you asap.

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