The type of rock bolt you choose depends on the specific application. For example, weight, location, and budget play a role in your selection.
Grout-anchored rock bolts
A grouted rock bolt is a steel threaded bar, also known as a rebar bolt. After drilling and inserting the steel rock bolts, cement grout or resin grout can be used as the grouting agent. A cable rock bolt made of steel wires intertwined as a steel rope is placed in the borehole with the grout for reinforcement. A bearing plate is used on the fully grouted rock bolt on the surrounding rock face to create tension and stabilise the rock.
Cable bolts
Cable bolts can be used to reinforce rocks temporarily or permanently. These rock bolts allow tensioning without the use of tensioners. Instead of the barrel and wedge system that is commonly found, they have a free length or threaded anchorage. Even when using longer cable bolt lengths, this allows for a more flexible system. Cable bolts are lightweight but have a high load-bearing capacity. Cement cartridges, resin cartridges, cement grout, or injection resin can be used to complete the installation. These rock bolts are ideal for situations with limited space and are useful for reinforcing roadways and gateways.
Hollow rock bolts
These steel rock bolts have a hole in their centre and were designed to ensure a dependable grouting process. The hole is used for grout, which eliminates tangled tubes. The same cone and wedge anchor mechanism can be used for this type of rock bolt. When the rock bolts face downward, grout is applied to the hole, and a short tube is inserted to remove any trapped air. When the rock bolts face up, a short tube is used for grouting, and the central hole is left open to accommodate a breathing tube.
Self-drilling rock bolts
These rock bolts are constructed from a hollow bar that is fully coarse threaded. It can be used in roof and wall bolting, in the ground, for grout installation, and can be installed temporarily or permanently. A self-drilling rock bolt serves as the drilling rod, anchor rod, and grouting pipe. To extend the length of a tendon, a splicing system is available. These rock bolts have diameters ranging from 25 to 76 and can be found with a trapezoidal or rope tread profile.
Mechanically anchored rock bolts
Instead of grout, this type of rock bolt uses an expansion shell. The wedge attached to the bolt shank is pulled into a conical shape as the rock bolt is rotated. Friction and interlock are used to secure the shell. A hanger or faceplate can be used to tension the mechanical anchor. This will more evenly distribute the load along the rock face, providing rock reinforcement.
Friction-anchored rock bolts
One of the most recent advancements in rock bolt techniques is the friction-anchored rock bolt. Along the entire length of the rock bolt, a radial force is applied to the borehole wall. After bolt installation, this creates frictional resistance to sliding.
MDX bolts
The MDX rock bolt will provide more ground support stability if working in an area with seismic rock conditions. Seismic events make working beneath the ground even more dangerous, and it is critical to use a rock bolt that can withstand the squeezing environment. The MDX rock bolt has a large expansion and load-bearing capacity and can be installed in a single pass. The design allows the rock bolt to handle significant loads with minimal displacement. The spatial wedge on these bolts can expand up to 60 mm. This creates a strong anchor in the wall without the use of grout or resin.
Fibre-reinforced polymer composite rock bolts
Steel rock bolts deteriorate quickly when exposed to harsh environmental conditions, such as in coal mines. In some cases, they can fail in a matter of days. Because of their corrosion resistance, fibre-reinforced polymer (FRP) rock bolts can perform better in these harsh conditions. As a result, they are better suited to harsh chemical and alkaline environments. In addition, these rock bolts are non-conductive, lightweight, simple to install, long-lasting, dimensionally stable under thermal loading, anti-static, and can be cut without sparking.
Dowels
A dowel is simply an untensioned steel rod that is grouted into the borehole after being drilled into the rock mass. It is not threaded, lacks an anchor head, and requires ground displacement to activate. Dowels will withstand shear and tensile stresses when joints are subjected to displacement. The shear-tensile stress ratio will be determined by the grout material and the composition of nearby ground support.
Rock bolt reinforcements
To further strengthen rock bolts’ reinforcement capacity, they are often combined with additional fixtures for greater safety.
Sprayed concrete
Once rock bolts are installed, this fast-hardening material is sprayed over the tunnel to provide additional stabilisation. This is available as gunite, a dry mix, and shotcrete, a wet mix. Shotcrete is more efficient because it has a lower rebound rate. Gunite is typically used when high strength is required in a small area.
Gunite is left dry until it reaches the nozzle, where water is added to the mix just before it is applied at high velocity to the substrate. Shotcrete is used for larger areas and necessitates the use of a mechanised nozzle because the mixture is heavy and cannot be carried by a worker. This pre-mixed material is made up of cement, aggregate, and water. The shotcrete is mixed with air and accelerators just before being sprayed. Fibres are sometimes added to shotcrete to make it stronger and more durable.
Lattice girders
Lattice girders are lightweight triangular steel frames that provide immediate support. These are commonly used in crown heading excavation and can be used in addition to shotcrete. This product
can be used in conjunction with strata bolts inserted through the lattice girders to provide additional forward support.
I-beam girders
I-beam girders are substantial steel frames and can be used to form an arch that spans the entire width of the tunnel. They are used when rock formations are weak, but their shape degrades shotcrete quality.
Contact Reunko Steel for details
Reunko Steel offers high-quality rock bolts and can design and install them to your specifications.
Our rock bolts are manufactured from hot-rolled high-tensile steel deformed bar and are available in standard lengths ranging from 0.6 metres to 3 metres. In addition, our standard lengths are colour coded for simple identification. We can also colour code your load indicator washers. To find out more about our rock bolts, get in touch with one of our representatives today.