Rock Bolt Types: Which Rock Bolt Is Right for Mining and Tunneling?

What Is a Rock Bolt?

Rock bolts are meant to reinforce ground, installed into a drilled hole. They help stabilize the rock mass around them.

A rock bolt differs from a structural prop, which bears against an excavation from below.

Rock bolts work with the surrounding rock to restrain fractured blocks, tie weaker layers into stronger ones, improve confinement, or transfer load from an unstable zone into a more stable zone of rock mass. A simple installed rock bolt system looks like:

Rock Mass → Borehole → Bolt → Anchoring Medium → Bearing plate → Nut

Varies based on type of bolt. Some are dependent on resin or cementitious grout as the bonding agent. Some expand mechanically, or rest on frictional contact between bolt and borehole wall.

Remembering that difference is one of the easiest methods of rock bolt classification.

Main Types of Rock Bolts

The terminology used for rock bolts can vary between countries, mines and engineering specifications.

Some systems are classified according to the anchoring mechanism, while others are identified by bolt material or construction.

The following comparison gives a practical overview.

These categories are not always mutually exclusive. For example, a threaded steel rock bolt may also be fully resin grouted.

That is why engineers normally define bolts through several parameters rather than only by product name.

1. Resin-anchored rock bolts

Resin bolts are a common type of underground ground support.

They work by placing a resin cartridge into the borehole before inserting the bolt itself. As the bolt is installed, it mixes the resin allowing the anchoring material to cure around the bolt shaft.

Once set, load is transferred from the bolt to the surrounding rock via the cured resin.

This allows the resin system to be engineered as a point anchor, partial- column anchor, or full column anchor depending on application needs.

Resin cartridge diameter, mixing time, installation time, and other parameters should match the bolt and installation procedure.

Mixing times will vary based on cartridge size and ambient temperature conditions.

Wanfeng supplies grouting and anchoring materials that can be used to supplement ground support solutions.

When should resin bolts be considered?

Ans. Many ground support applications consider resin bolts for mine roof support, underground roadways, tunnels, and other applications where rapid and efficient installation is important.

As always, geological conditions and engineering design may affect their suitability.

2. Mechanical rock bolts

Mechanical rock bolts achieve anchorage with a mechanical device placed in the borehole.

Systems commonly use an expansion mechanism that “grasps” the surrounding rock when the bolt is tensioned.

Load transfer can therefore be focused at the anchorage point initially, unlike a fully grouted bolt.

Advantageously, this can provide immediate support after installation if ground conditions allow.

However, mechanical anchorage is more sensitive to factors like borehole geometry and competence of rock near the anchoring point.

Weak or fractured rock could require alternative anchoring techniques.

Certain mechanical bolts can be grouted as part of a ground support design. Mechanical bolts can also use grout if additional protection or rock bonding is required.

3. Friction rock bolts

Friction bolts achieve load transfer through surface contact along the bolt and borehole wall.

Instead of resin or expanding shells, friction bolts are installed so that they “press” against the borehole wall. Resistance is created along the length of contact between bolt and rock.

These types of bolts are often associated with underground mining applications. This is because friction bolts can be installed quickly when specialized equipment is used.

Friction rock bolts are also capable of tolerating some degree of movement. This makes them ideal for certain support applications where deformation is expected.

Keep in mind that diameter and fit up of the borehole is crucial for friction bolts.

If the diameter is too large or not constructed within specified tolerances, proper friction may not be achieved between bolt and borehole wall.

Point being, friction bolts should not be selected by nominal diameter alone.

Procurement teams should evaluate installation equipment and specify suitable borehole diameter alongside the bolt size.

4. Fully grouted rock bolts

Fully grouted bolts are embedded with anchoring material along most or all of their length in the ground.

Grouting material can be either resin or cementitious material based on system design.

Full grouting helps distribute load across a larger section of reinforcement, rather than focusing loads at the anchorage point.

Fully grouted bolts have been used extensively for mining, tunneling, and geotechnical projects.

One advantage of full grouting is that it can integrate more evenly with the surrounding rock. Creating a solid load path back to the support system.

It should be noted that correct installation is still critical for full grouted bolts.

Factors like borehole preparation, grout distribution, and installation procedures affect performance.

Void spaces or insufficient coverage could compromise load transfer mechanisms.

Explore cementitious grouting materials for ground support where appropriate.

5. Threaded steel rock bolts

Threaded rock bolts are steel bars with threads along specific lengths or the entire length of the bolt.

These threads allow nuts, plates, and other components to connect to the bolt easily.

Threaded bolts are advantageous because connections can be made at the surface. A basic full grouted threaded system could consist of:

Threaded bolt + resin/grout + bearing plate + washer + nut

Remember that load is ultimately transferred through the entire system.

A threaded bar can be resin anchored, cement grouted, installed as a friction bolt, or used with another engineered solution.

Threaded describes the bar construction more than the anchoring method.

Threads allow bars to be used with a range of accessories and plate configurations.

Threaded bars can be cut to length or used as-is for international projects with configurable plate and nut options.

Our ground support service catalog includes resin bolts, FRP bolts, and threaded bar systems.

6. Hollow grouting anchors

Hollow grouting anchors are bar types that include a central bore through the bar.

During installation, the hollow center can be used to inject grout into the ground along with the reinforcement bar.

This can be very beneficial if grouting the ground around the anchor is required.

Typical solid bars require separate grout hoses or channels to achieve the same effect.

Installing hollow bars simplifies the system by combining reinforcement and grouting materials.

Similar to other anchor bars, geological conditions will dictate if hollow bars can be used.

They can be used in tunneling applications, slope support, underground construction, and challenging ground conditions.

Parameters to consider when comparing include bar size, desired load capacity, borehole conditions, grout materials, anchor length, and installation process.

Hollow grouting anchors show why rock bolt selection should consider the full installation system.

Grout chemistry and installation equipment are just as important as steel diameter.

View our rock bolting and anchoring solutions for compatible system configurations.

7. FRP rock bolts

FRP rock bolts use fiber reinforced polymers instead of conventional steel.

Rather than heat-treated steel alloys, FRP bolts are constructed from composite material.

Applications can benefit from FRP bolts because of low weight, cuttability, or corrosion resistance.

Cutability may allow subsequent excavation through the bolt without affecting overall strength of the support system.

Just one example of how FRP bolts can be used differently than steel.

Remember that FRP and steel bolts will have different mechanical properties.

Engineering teams should review tensile strength requirements, deformation characteristics, chemical compatibility, and exposure conditions before replacing steel with FRP.

Learn more about FRP rock bolt systems offered by Wanfeng.

Rock Bolt vs Roof Bolt: Is There a Difference?

Roof bolt is often used interchangeably with rock bolt, but the terms are not always synonymous.

Rock bolt refers generically to any reinforcement element which is installed into rock.

Roof bolt more commonly describes a bolt installed in the roof of an underground mine, roadway, tunnel or other underground excavation.

Essentially all roof bolts can be considered rock bolts. Rock bolts are also installed in sidewalls, slopes and various other orientations.

Rock Bolt vs Cable Bolt

Rock bolts can be further differentiated based on material type, diameter and intended engineering use.

Stand-alone rock bolts are typically rigid bars used to provide active support/reinforcement around an excavation.

Cable bolts can be made of steel strands or cable-style reinforcement material. Cable bolts are frequently used when a longer length of reinforcement is needed, or deeper anchorages are required.

Point-Anchor vs Fully Grouted Rock Bolts

Rock bolts can also be installed with different anchoring techniques.

With point anchored bolts, a significant portion of the anchoring force is provided at one section along the borehole.

Fully grouted bolts, also known as full column bolts, create a bond between grout and bolt over a large portion (if not all) of the bolt length.

Factors affecting bolt type decision:

Do your ground stress conditions include rockbursts? If so, completely grouted rock bolts are likely required.

Are deformable anchors ever required for the project? If so, you may need to consider point-anchor bolts with elastic plate or special socket.

Both point-anchor and fully-grouted rock bolts have important uses, and one is not inherently better than the other.

Why the Bearing Plate Matters

The rock bolt is just one component of a complete ground support system.

At the surface of the excavation, rock bolts usually rely on a plate to help spread the load from the bolt/nut out across a wider area of rock.

Excavation Surface

This plate must be selected to match the intended bolt size, hole diameter and anticipated loading conditions.

See Wanfeng’s full range of support plates and rock bolt accessories.

Companies like Wanfeng offer complete support plates and rock bolt accessories. These include flat bearing plates, butterfly anchor plates, domed plate washers and much more.

Rock bolt plates can have a huge impact on the performance of your complete ground support assembly. For example, Wanfeng’s flat bearing plate for mining roof bolts :

Can be installed with optional plate separators to help prevent plate rocking or rotation.

Helps spread the load from the bolt across a wider rock surface.

Customizable by plate size, thickness and hole diameter to match project specifications.

Tips on Selecting the Proper Rock Bolt Type

Don’t ask us what’s “the best” rock bolt.

Ask us about your project’s geotechnical needs.

When preparing an RFQ or engaging in a technical discussion, the following information is typically the most helpful: project application, rock conditions, bolt dia. & length, borehole dia., mechanical property requirements, anchoring method, plate dimensions, thread type, corrosion requirements, installation equipment, required quantity & available drawings.

Simply stating “We need 5,000 mining rock bolts.” leaves us guessing.

Including mine or tunnel application, bolt geometry, material / load requirements, resin/grout system, plate requirements, and relevant drawings allows us to be specific.

This ensures you don’t mix and match incompatible components.

Wanfeng also offers engineering services for ground support as well as OEM services for customized rock bolt specifications, non-standard components and project specific configurations.

Rock Bolt Selection by Application

Different applications usually create different reinforcement priorities.

These are general selection concepts rather than design specifications.

Actual bolt type, dimensions, spacing and installation pattern should be determined from the project’s geological investigation and engineering design.

Rock Bolts Often Come as Part of a Ground Support System

Purchasing a rock bolt as if it was a standalone product is a very common mistake.

A complete underground support solution may include:

Rock Bolt → Resin/Grout → Bearing Plate → Nut → Mesh → Steel Strap

The resin or grout is the load transfer medium.

Different materials are used for different reasons.

The bolt strengthens ground.

The plate helps distribute load against the rock surface.

Mesh can be used to help control falling rocks between bolts.

Steel straps allow you to join multiple support points.

Additional steel members can be added for added structure where required.

Considerations like these are critical when mining companies, contractors and distributors purchase components from foreign vendors.

Browse Wanfeng’s full range of ground support products to help source additional compatible components.

Common Mistakes When Specifying Rock Bolts

Many procurement problems originate before manufacturing begins.

Simply choosing a bolt based on diameter can cause problems later if borehole diameter is not specified, plate-hole compatibility is overlooked, resin is ordered without considering bolt and hole size, mixed components that have been designed to different thread standards are used, corrosion requirements are not indicated or changes are made to one component without reviewing related components.

The best option is to provide a complete ground support specification if at all possible. Technical drawings become even more important if non-standard dimensions are required.

Rock Bolt Ordering Checklist

As much of the following information as possible:

1. Application: underground mine, tunnel, slope, highway excavation, etc.
2. Rock bolt type: resin anchored, fully grouted, mechanical anchor, threaded steel, hollow, FRP (carbon fiber or fiberglass) or another specified type.
3. Length and diameter.
4. Steel/composite grade and strength requirements.
5. Thread size or thread standard.
6. Required borehole diameter.
7. Anchor type: resin capsule, cement grout, mechanical anchor or another specified medium.
8. Plate size and hole diameter.
9. Nut and washer details.
10. Surface treatment/corrosion requirements.
11. Quantity required and desired delivery date.
12. Engineering drawings or other standard/specifications that the parts must meet.

Providing as much information as possible will allow for quicker technical review and faster quoting.

FAQ

1. What are the different types of rock bolts?

Rock bolts can be categorized in many ways but common classifications are:

• Resin anchored rock bolts
• Mechanical anchor rock bolts
• Friction bolts
• Fully grouted rock bolts
• Threaded steel bolts
• Hollow grouting anchors
• FRP (carbon fiber or fiberglass) bolts

This list is not exhaustive and the terminology can be confusing because bolts can also be categorized by material, anchoring method and method of construction.

2. What rock bolt should I use?

It depends on the application. Different bolt types are better suited to different rock mass qualities, required load capacities, tolerable deformation levels, borehole conditions and available installation equipment. The overall ground support design is also a major consideration.

3. What is the best rock bolt for underground mining?

There is no single “best” rock bolt for underground mines. Conditions vary from property to property and even between areas of the same mine.

4. What is a resin rock bolt?

A resin rock bolt uses a resin cartridge placed in the drill hole to adhere the bolt to the surrounding ground. Anchorage length can vary depending on the design and support requirements.

5. What is a friction rock bolt?

Friction rock bolts create their anchor resistance via contact with the drill hole wall rather than relying mainly on resin or mechanical expansion device.

6. What is a fully grouted bolt?

A fully grouted bolt is adhered to the ground along most or nearly all of it’s grouted length. Fully grouted rock bolts are usually bonded using either resin or cement grout.

7. Are rock bolts and roof bolts the same thing?

Roof bolts are typically rock bolts which are placed into the roof of an underground excavation. Rock bolts may also be used in the sides of openings, slopes or other surface and underground excavations.

8. What is the difference between rock bolts and cable bolts?

Rock bolts are generally rigid support members. Cable bolts are made from multiple flexible steel strands. Cable bolts can be used to reinforce longer distances or deeper based on engineering design.

9. Can rock bolt specifications be tailored to project requirements?

Yes. Many attributes of rock bolts can be modified to meet specific engineering and project requirements. Diameter, length, materials, thread type, plate size, surface treatment and more can be customized. Wanfeng even lists customized rock bolt specifications as one of our engineering and OEM services.

Need Rock Bolts for a Mining or Tunneling Project?

Choosing the right rock bolt is more complicated than finding a bolt diameter you like.

The rock bolt, resin or grout, drill hole diameter, plate size, nut and surrounding mesh or reinforcement work together to create a complete ground support system.

At Hebei Wanfeng Machinery Manufacturing Co., Ltd we offer complete underground ground support solutions for mining and tunneling projects. Our product families include rock bolt systems, cable anchoring systems, plates and accessories, grouting products, mesh and other supportive components.

Send us information about the application including technical specifications, engineering drawings, quantity requirements and installation requirements for project evaluation.

Explore: Rock Bolting & Anchoring Systems
Related Guide: What Is Ground Support?
Accessories: Rock Bolt Plates & Accessories
Anchoring Materials: Grouting & Anchoring Materials
Engineering Support: Ground Support Engineering & OEM Services