Classification and Selection of TBM Cutter

In tunnel boring machine (TBM) construction, cutters are not merely accessories—they are the business end of the entire operation. Every meter of tunnel advance depends on the interaction between the cutter and the rock face. Selecting the wrong cutter type for the prevailing geology can lead to slow advance rates, excessive wear, frequent cutter changes, and ultimately, project delays that cost millions.

This article provides a practical framework for understanding TBM cutter classification and making informed selection decisions based on geological conditions, machine specifications, and project requirements.

TBM Cutter Classification

TBM cutters can be broadly divided into two categories based on their rock-breaking mechanism: roller cutters (disc cutters) and soft ground cutters (scrapers and cutting tools).

1. Roller Cutters (Disc Cutters)

Roller cutters are rock-breaking tools that rotate with the cutterhead and spin on their own axes during excavation. They apply high contact forces to the tunnel face, inducing tensile and shear fractures in the rock.

1.1 By installation position:

1.2 By cutter ring material:

• All-steel roller cutters: Steel cutter rings for softer or less abrasive formations

• Tungsten carbide insert (TCI) roller cutters: Steel rings with carbide inserts for hard and abrasive rock

1.3 By blade/profile shape:

• Disc cutters: Featuring a continuous steel or TCI ring

• TCI roller cutters: Featuring steel teeth or button-type inserts

1.4 By structural form:

• Single disc cutter: One cutter ring per assembly—preferred for hard, intact rock with UCS >100 MPa

• Double disc cutter (twin disc cutter): Two rings per assembly—better suited for mixed ground or soft-hard transition zones

• Triple disc cutter (triplet disc cutter): Three rings per assembly—for specific soft ground applications

Recent research indicates that double-edge cutters can reduce per-edge wear by 46–66% compared to single-edge designs due to load redistribution. However, in competent hard rock, single disc cutters are generally preferred due to their higher load capacity per cutting path.

1.4 By cutter ring profile (disc cutter subtypes):

CCS cutters are preferred in practice because they are more resistant to abrasive rock characteristics and last longer than V-type discs.

2. Soft Ground Cutters

Soft ground cutters rotate with the cutterhead but do not spin on their own axes. They are designed for soil, clay, and soft rock formations where disc cutters would be ineffective.

Common types used on shield machines include:

• Scrapers: Remove excavated material from the tunnel face

• Cutting knives: Primary cutting tools for soft ground

• Tooth knives: Penetrate and break softer formations

• Leading knives: Pre-cut the face ahead of main tools

• Profiling knives: Shape the tunnel profile

• Edge scrapers: Clean the periphery

TBM Cutter Selection: A Geological Approach

Whether a TBM cutter is suitable for the project's geological conditions is one of the most critical factors affecting tunneling performance. The selection process must consider rock strength, abrasiveness, fracture frequency, and water conditions.

Selection Guide by Rock Type

Soft soil and soft rock formations (shale, clay, weathered rock, UCS <20 MPa)

• Recommended tools: Scrapers, toothed cutters, or chisel-type button roller cutters

• Rationale: These formations do not require high-impact fracturing; cutting and scraping tools are more efficient

Medium-soft rock formations (limestone, sandstone, mudstone, UCS 20–60 MPa)

• Recommended tools: Disc roller cutters or chisel-type button roller cutters

• Rationale: Disc cutters provide sufficient penetration while maintaining acceptable wear rates

Medium-hard rock formations (granite, schist, gneiss, UCS 60–150 MPa)

• Recommended tools: Disc roller cutters or spherical button roller cutters

• Rationale: Spherical buttons offer better resistance to impact and abrasion in harder formations

Hard rock formations (basalt, conglomerate, quartzite, UCS >150 MPa)

• Recommended tools: Disc roller cutters or spherical button disc cutters

• Rationale: High-strength rock requires cutters with maximum impact resistance and wear life

Additional Selection Factors

Rock strength (UCS): For rock strength ≥60 MPa, a single disc cutter is generally preferred. Double disc cutters work best in mixed ground or soft-hard transition zones. Hard rock formations typically require large-diameter double-edge cutters, while soft rock benefits from single-edge cutters combined with scrapers.

Abrasiveness: Highly abrasive rocks (high quartz content) require TCI cutters with wear-resistant carbide grades. Research shows that CCS cutters are more resistant to abrasive rock characteristics.

Cutterhead design: Cutter spacing and penetration depth must be optimized for the specific rock type. Optimal cutter selection in soft–hard composite strata should prioritize cutter force, with the greatest force required in hard rock.

TBM diameter: Smaller-diameter machines may require smaller-diameter cutters to ensure an optimal disc cutter profile.

Final Thoughts

TBM cutter selection is not a one-time decision—it is an ongoing process that requires continuous monitoring and adjustment as geological conditions change along the tunnel alignment.

The key takeaways are straightforward:

1. Match the cutter to the rock—soft ground needs scrapers and cutting tools; hard rock needs disc cutters with appropriate profiles

2. Choose the right profile—CCS cutters offer longer wear life; V-type cutters offer higher cutting efficiency

3. Consider single vs. double disc—single for hard rock (UCS ≥60 MPa); double for mixed ground

4. Monitor wear patterns—double-edge designs can reduce per-edge wear by 46–66%

5. Plan for cutter changes—center cutters, face cutters, and gauge cutters wear at different rates and require different replacement schedules

Proper cutter selection and maintenance directly impact advance rates, operating costs, and project timelines. As one study of 112 high-performing TBM projects concluded, selecting the appropriate cutter types and configurations is crucial for effective TBM operations.

For projects with variable geology along the alignment, consider a hybrid approach—using different cutter types on different parts of the cutterhead to match the expected ground conditions.

Frequently Asked Questions

Q1: What is the difference between a single disc cutter and a double disc cutter?

A single disc cutter has one cutter ring per assembly and is preferred for hard, intact rock with UCS above 60 MPa. A double disc cutter has two rings per assembly and works best in mixed ground or soft-hard transition zones. Double disc cutters can reduce per-edge wear by 46–66% due to load redistribution, but single disc cutters offer higher load capacity per cutting path in competent rock.

Read more: Factors Affecting TBM Cutter Tunneling Efficiency

Q2: How do I choose between CCS and V-type disc cutters?

CCS (Constant Cross Section) cutters are more resistant to abrasive rock and last longer, making them the preferred choice for most field applications. V-type cutters are more efficient in terms of cutter force but wear faster in abrasive conditions. For soft to medium-strength rock, CCS cutters are generally recommended.

Read more: The Working Principle of TBM Cutter Disc Used in Tunnel Engineering

Q3: What type of cutter should I use for hard rock like granite?

For hard rock formations such as granite (UCS >100 MPa), use single disc cutters or heavy-duty roller cutters with large diameter (19–20 inches) and high-wear-resistant rings. Spherical button disc cutters are also suitable for these conditions.

Q4: What tools are recommended for soft ground tunneling?

For soft soil and soft rock formations (shale, clay, weathered rock), use scrapers, toothed cutters, or chisel-type button roller cutters. These tools cut and scrape rather than fracture, which is more efficient in low-strength ground. Soft ground cutters rotate with the cutterhead but do not spin on their own axes.

Q5: How does cutter position on the cutterhead affect selection?

Center cutters break the central rock mass where rotational speed is lowest; face cutters handle the bulk of excavation; gauge cutters maintain tunnel diameter and control overbreak; reaming cutters are used for tunnel enlargement. Each position experiences different loads and wear patterns, requiring appropriate cutter specifications and replacement schedules.

Read more: Analysis of TBM and Roller Cutter Tunneling Process

References

1. Wear Phenomena in Tunnel Boring Machine (TBM) Hard Rock Drilling—Reasons and Consequences – SpringerLink, 2018. https://link.springer.com

2. TBM Excavation in Difficult Ground Conditions: Case Studies from Turkey – Wiley Online Library, 2016. https://onlinelibrary.wiley.com

3. Tool wear in TBM hard rock drilling – backgrounds and special phenomena – Wiley Online Library, 2018. https://onlinelibrary.wiley.com

4. Wear analysis for the selection of cutters for a Tunnel Boring Machine – Udima, 2026. https://udimundus.udima.es

5. Decision tree analysis of cutter selection for tunnel boring machines: A study of geological conditions and machine types in high-performing TBM projects – ScienceDirect, 2025. https://www.sciencedirect.com

6. Research on Rock-Breaking Characteristics of Cutters and Matching of Cutter Spacing and Penetration for Tunnel Boring Machine – MDPI, 2024. https://www.mdpi.com

7. Wear Characteristics of TBM Disc Cutter Ring Sliding against Different Types of Rock – ScienceDirect, 2025. https://www.sciencedirect.com

8. Wear Prediction and Mechanism Study of Tunnel Boring Machine Disc Cutter Breaking in Hard–Soft Rock Considering Thermal Effect – MDPI/DOAJ, 2025. https://www.mdpi.com

9. Probabilistic analysis of the disc cutter failure during TBM tunneling in hard rock – ScienceDirect, 2021. https://www.sciencedirect.com

10. A study on predicting the wear of TBM disc cutters using Cerchar testing – ScienceDirect, 2023. https://www.sciencedirect.com

11. TBM disc cutter ring type adaptability and rock-breaking efficiency: Numerical modeling and case study – KoreaScience. https://koreascience.kr

12. Design Aspects Governing Disc Cutters and Cutterheads of Hard Rock TBM—A Review – SpringerLink (Mining, Metallurgy & Exploration), 2024. https://link.springer.com

13. Influence of Two Gage Disc Cutters on TBM Performance and Optimization of Disc Cutter Installation Angle – SpringerLink (Rock Mechanics and Rock Engineering), 2025. https://link.springer.com

14. Evaluation on rock-breaking performance of different TBM disc cutters based on full-scale rotary cutting test and discrete element method – SpringerLink (Acta Geotechnica), 2026. https://link.springer.com

15. Investigation of the Influence of Cutter Geometry on the Cutting Forces in Soft–Hard Composite Ground by Tunnel Boring Machine Cutters – MDPI, 2024. https://www.mdpi.com