Beneath one of Canada’s busiest city centers, crews faced a problem that most tunneling professionals would expect only explosives to solve. A major Canadian contractor needed to excavate a deep shaft and drive a 117 yds (107m)-long metro tunnel, that is 32.8ft (10m)-wide and 23ft (7m)-high, through rock with uniaxial compressive strengths (UCS) ranging from 100MPa to 170MPa.
This exceeded the limits traditionally considered possible for mechanized excavation technology like drum cutters or roadheaders.
The location in Montreal made the challenge even greater. Working directly under busy city streets meant vibration and noise had to be kept to a minimum, with no margin for error given the risk of damage to surrounding buildings and utilities. Drill and blast was ruled out from the start, not only for environmental and regulatory reasons but also for the logistical challenges explosives would pose in such a dense urban setting. The contractor needed a method that could cut hard rock cleanly, efficiently, and quietly, all while minimizing the impact on the city streets above.
The solution to the different needs for the metro excavations and their setting was to use Antraquip’s AQ 6 transverse drum cutter. Weighing approximately 8t and capable of delivering over 400kW of cutting power, the AQ 6 is a leader in power and performance within its class. For the project, the high powered drum cutter was mounted on a CAT365 excavator and powered by a dedicated hydraulic power unit. This configuration provided maximum stability, reach, and sustained performance in the face of constant high load cutting. The reinforced drums and robust transmission were engineered for prolonged operation in hard rock, giving the cutter the durability needed to take on a job like this.
The excavation began with the shaft before advancing into the tunnel heading. The site team followed a disciplined cycle – positioning the cutter for optimal engagement, maintaining steady feed pressure to balance penetration and tool life, while performing regular inspections to maintain the drums and cutter bits in peak condition. Dust suppression and ventilation were closely managed to ensure a safe working environment underground.
Despite the extreme conditions, the AQ 6 drum cutter delivered average production rates of ~12m3 per hour, with higher outputs achieved under optimal conditions. The shaft and tunnel were completed on schedule, and the resulting profile was smooth and accurate, with minimal overbreak. This reduced the need for additional support and cleanup work, while low vibration levels allowed excavation to proceed without disruption to the city above.
For the contractor and for Antraquip, this project represented more than a normal successful outcome. It challenged long held assumptions about the capabilities of drum cutters in hard rock.
Rock cutting at UCS levels exceeding 100MPa had long been considered the territory of heavy roadheaders (100t or larger) or explosives, but the Montreal tunnel demonstrated that with the right equipment, setup, and operational approach, Antraquip drum cutters (roadheader attachments) can perform in these conditions. The project also underscored the importance of close collaboration between supplier and contractor. Engineering decisions made early in the process had a direct impact on production, efficiency, and tool longevity.
As urban infrastructure projects become more complex and restrictions on disruptive excavation methods increase, solutions like this are becoming more valuable. Advanced rock cutting technology offers a cleaner, safer, and often faster alternative, especially in sensitive environments. This Montreal metro ventilation tunnel project stands as a case study in pushing the boundaries of what is possible in underground construction.
IMPACT ON FUTURE PROJECTS
The success of the Montreal ventilation tunnel has influenced how contractors and engineers approach excavation in extreme hard rock. By demonstrating that a high powered drum cutter could maintain steady production in UCS ranges traditionally reserved for drill and blast, the project expanded the possibilities for advanced rock cutting methods in sensitive, high density urban environments.
A key part of that success was the AQ 6’s engineering. Its robust transmission, reinforced drums, strategically designed pick configuration, and dedicated hydraulic power unit created a combination capable of sustained operation in some of the toughest ground conditions. This performance has set a new benchmark for what can be achieved when a cutter combines power with a design tailored to its geology. Contractors who once deemed this type of work impossible without blasting now see advanced drum cutters as a practical and, in many cases, preferred solution.
Since Montreal, similar strategies have been used on projects where precision and vibration control were critical.
In Chicago, the Transit Authority needed to remove a 100 year old concrete embankment wall directly adjacent to existing buildings and infrastructure. The wall ranged from 18 inches to six feet thick, with some sections just inches from nearby structures. Seismic monitoring stations were installed to protect the surrounding infrastructure. Conventional demolition tools, like pneumatic hammers, were ruled out due to excessive vibration. The solution chosen was to use an Antraquip AQ 4 hydraulic drum cutter, which delivered controlled grinding of the thick concrete into manageable debris while keeping vibration well within seismic limits. The project was completed safely, efficiently, and without damage to nearby structures, proving the value of precision cutting in sensitive urban environments.
This type of application reinforces the importance of early collaboration between equipment suppliers and project teams to fine tune machine configuration, tool selection, and operating parameters. As infrastructure projects face greater scrutiny for environmental impact and safety, the strategies proven in Montreal and successfully applied in projects like Chicago offer a reliable model for delivering on schedule and within budget while minimizing disruption. The outcome shows that with the right technology and expertise, even the most challenging ground conditions can be tackled efficiently to create safer and more sustainable underground construction.
