Rock anchors and Self-Drilling Anchor (SDA) systems are widely used in tunneling, slope stabilization, mining, and foundation reinforcement. In modern geotechnical engineering, rock anchors play a critical role in stabilizing rock masses and ensuring structural safety in both temporary and permanent applications.
Unlike conventional systems, SDA rock anchors integrate drilling and grouting into a single operation. Their performance depends not only on steel grade but also on manufacturing process and installation conditions. Therefore, selecting materials for rock anchors requires a systematic evaluation of steel grade, manufacturing method, and ground conditions, rather than relying solely on strength values.
1. Self-Drilling Hollow Bar Steel Grades (SDA Systems)
Rock anchors using SDA systems are manufactured from a wide range of global steel grades, depending on regional standards and production capabilities.
Common steel grades include:
- 28Mn6
- 37Mn5 / J55
- 40Cr / 41Cr4
- N80
- S45E (45#)
- S355N (Q355B equivalent)
- S460N
These materials can generally be used for rock bolt systems. However, selection must consider working conditions, welding requirements, and manufacturing process routes.
2. Application Standards by Engineering Type
Different applications follow different design and execution standards:
Rock Bolts
- ASTM F432 – Standard Specification for Roof and Rock Bolts and Accessories
Soil Nailing
- BS EN 14490 – Special Geotechnical Works Executions – Micropiles
- FHWA-NHI-14-007 – Soil Nail Walls Reference Manual
Micropiles
- BS EN 14199 – Construction of Special Geotechnical Engineering – Micropiles
- FHWA NHI-05-039 – Micropiles Design and Construction Manual
3. Steel Grade Is Not the Only Controlling Factor
Steel grade alone does not determine anchor performance.
Anchor behavior is influenced by:
- Steel chemical composition
- Manufacturing process
- Heat treatment condition
- Cold/warm/hot working processes
4. Effect of Manufacturing Process on Performance
Cold Rolling
Typical steels:
- 28Mn6
- 37Mn5
- J55 / N80
Characteristics:
- Work-hardened condition after processing
- Strength increased through strain hardening
- Cold extrusion further increases yield strength
Advantages:
- Higher tensile strength
- Lower production cost
Disadvantages:
- poor plasticity
Suitable for:
- Rock bolts
- Temporary or medium-load applications
Warm Rolling
Applicable steels:
- 28Mn6
- 37Mn5
- J55
- N80
- 40Cr
- S45E
Advantages:
- Better ductility than cold-formed products
- Easier installation and deformation adaptability
Disadvantages:
- The strength is not too high
Suitable for:
- Soil nails
- Complex ground conditions
- Medium deformation requirements
Hot Rolling + Heat Treatment
Applicable steels:
- All above grades depend on the heat treatment process
Characteristics:
- Final properties controlled by quenching and tempering
- Strength–ductility balance can be optimized
Advantages:
- Highly tunable mechanical properties
- Reliable performance in demanding geotechnical conditions
Disadvantages:
- Complex manufacturing process
- Requires advanced production capability
Suitable for:
- Micropiles
- High-load structural reinforcement
5. Engineering Understanding of Rock Anchor Steel Grades
Same steel grade ≠ , same rock anchor performance
Even with identical steel grades:
- Cold-formed and heat-treated rock anchors behave differently
Alloy steel vs low-alloy steel vs carbon steel in rock anchors
Material type alone does not determine rock anchor quality.
| Material type | Key influencing factor |
| Alloy steel (40Cr, 28Mn6) | Heat treatment + processing quality |
| Low-alloy steel (S355N, S460N) | Ductility + weldability for rock anchors |
| Carbon steel (C45) | Cost + basic strength level |
Key conclusion:
Manufacturing quality control is often more important than steel grade in rock anchor performance.
Conclusion
The selection of materials for rock anchors is not determined by steel grade alone, but by a combination of manufacturing process, construction conditions, and long-term service environment. Different rock anchor applications prioritize different performance requirements: rock bolts emphasize load capacity and installation efficiency, soil nails require ductility and weldability, while micropiles demand high structural reliability and durability. In practice, a reliable selection strategy depends on stable products and mature manufacturing processes to ensure safety and long-term performance under complex conditions.
ONTON specializes in geotechnical anchoring solutions, providing self-drilling hollow bars and anchors for rock bolts, soil nails, and micropiles. Technical support for material selection and process optimization is available. For technical information or engineering consultation, please contact our team.
