The ground abrasiveness It directly affects the wear on a tunnel boring machine’s cutterhead, discs, picks, scrapers, teeth, guards, and excavation components. The more abrasive the ground, the greater the tool wear, spare part consumption, cutting torque, maintenance downtime, and the risk of performance loss during pile driving or microtunneling.
In projects of pipe ramming, microtunneling in terrestrial and subway applications o infrastructure crossings, abrasiveness must be assessed during the geotechnical phase in order to select the appropriate tunnel boring machine, design the cutting head, and plan for access points, spare parts, maintenance, and potential interventions.
Why Abrasiveness Is Critical in Microtunneling
In a trenchless project, direct access to the working face may be limited or nonexistent, especially in closed shields. If the ground wears down more than expected, this can lead to a loss of performance, increased thrust, operational deviations, prolonged downtime, or the need to change tools under challenging conditions.
That is why abrasiveness does not only affect the cutting tool. It also influences:
- Daily production.
- Tool wear.
- Preventive maintenance.
- Cutting pair.
- The necessary push.
- Cost of replacement parts.
- Stop Planning.
- Risk of jamming or loss of forward motion.
- Choice of open shield, EPB, or hydroshield.
The choice of tunnel boring machine You should consider abrasiveness along with soil strength, grain size, the presence of rock and boulders, the water table, and the stability of the cutting face.
What data can be used to assess abrasiveness?
To assess the risk of wear and tear, the following are primarily reviewed:
Type of soil or rock:
Siliceous sands, gravel, quartzite, granite, hard rocks, or soils with a high quartz content tend to increase wear.
Particle size and mineralogy:
Particle size, grain shape, and the presence of hard minerals affect the abrasion on the cutting head.
Strength of rock or cemented soil:
More resistant or case-hardened materials may require specific tools and greater cutting forces.
Presence of boluses or blocks:
Bumps can cause impacts, uneven wear, tool breakage, or sudden increases in torque.
Abrasiveness tests:
When the project requires it, specific tests can be used to estimate potential wear and aid in tool selection.
Water table and pumping system:
The presence of water and the transport of excavated material can affect the behavior of fine particles, the cleanliness of the chamber, and component wear.
How Tool Selection Affects the Process
Depending on the abrasiveness and type of terrain, different configurations can be selected:
Cutting discs: commonly used in rock or hard ground, where the material needs to be broken up.
Picks, teeth, or rippers: used on hard surfaces, cement-based materials, or mixed soils.
Scrapers: They help clean, convey, and transport the excavated material to the extraction system.
Abrasion-resistant protections: plates, reinforcements, armor, or wear-resistant materials to protect the cutting head and exposed areas.
Combination tools: useful in mixed terrain, with alternating soil, rock, boulders, or heterogeneous materials.
In highly abrasive conditions, the selection should not be based solely on “cutting through the material,” but rather on maintaining production, minimizing downtime, protecting the machine, and ensuring that the system can operate safely until the end of the run.
What risks arise if abrasiveness is underestimated?
Underestimating abrasiveness can lead to:
- Premature tool wear.
- Increase in cutting torque.
- Lower feed rate.
- Higher energy consumption.
- Increase in thrust.
- Unplanned stops.
- Difficulty maintaining alignment.
- Damage to the cutting head or chamber.
- Additional costs for replacement parts and repairs.
- Risk of not completing the section as planned.
In construction projects with EPB tunnel boring machine o hydro-shield for water-logged terrain, this analysis is particularly relevant because modifications to the cutting head can be more complex than in systems with direct access.
How to Manage Wear and Tear Risk
To manage wear and tear, it is recommended that you:
- Include abrasion tests in the geotechnical investigation when there is a risk.
- Examine the mineralogy, grain size distribution, strength, and presence of quartz.
- Select a cutting head that is compatible with the terrain.
- Plan for replacement parts and a maintenance strategy.
- Define intervention points or procedures if the section requires them.
- Monitor cutting torque, thrust, feed rate, and energy consumption during excavation.
- Adjust the feed rate, pressure, and extraction parameters based on the actual behavior of the soil.
Minimum checklist for assessing abrasiveness: soil or rock type, quartz content, grain size, strength, boulders, blocks, tested abrasiveness, water table, penetration depth, diameter, tunnel boring machine type, planned tools, accessibility to the tunnel face, spare parts, expected cutting torque, and maintenance plan.
Request a Technical review of abrasiveness, wear, and cutting tool selection before specifying the tunnel boring machine or finalizing the technical and commercial proposal.
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