Under high cover, fractured rock you want the best ground support, period. Whether the challenge is rock bursting or non-self-supporting ground, The McNally Support System has you covered. Get the system that made the world’s second deepest tunnel a success, more than a mile below the Andes Mountains.
The McNally Support System is the simplest way to increase advance rates and maintain worker safety on Main Beam machines in difficult conditions where roof shield fingers often bend or break under the weight of pressurized rock. Designed and patented by C&M McNally of Ontario, Canada for exclusive use on Robbins TBMs, the McNally system has been tested and proven on projects worldwide.
By replacing the roof shield fingers on a Main Beam TBM, the McNally system prevents rock movement in the critical area immediately behind the cutterhead support. Shield fingers are switched out with a curved assembly of pockets with rectangular cross-sections. The pockets extend axially aft from the rear side of the cutterhead through the cutterhead support, in the area where roof drills could work.
Workers insert pre-fabricated steel slats into the pockets prior to a TBM stroke. The ends of the slats protrude from the pockets so they can be bolted to the roof of the tunnel using a steel strap. As the machine advances, the slats are pulled from the pockets and continuously bolted to the roof using subsequent straps. The result is effective containment of loose and unstable rock. The system can be used in the crown area, as well as along the tunnel side walls, depending on ground conditions.
Expecting difficult ground conditions on your next project? The McNally Support System is easy to use and doesn’t require extensive training. The system utilizes the same steel strap and rock bolt ground support method already used throughout the industry. Dynamic ground support systems are also available, allowing you to use the McNally system only when necessary.
The McNally Support System effectively contains fractured rock and keeps it where you want it—in the tunnel crown and within the tunnel profile. Since the system uses no roof shield fingers, crew members can fully tighten rock bolts and secure slats to the tunnel immediately following excavation, when ground support is most critical.
In tunnels worldwide, the McNally Support System has proven its durability and ease of use. At Peru’s Olmos Trans-Andean Tunnel, crews used the system to control rock 2,000 m below the Andes in rock bursting conditions. In multiple tunnels in China, the system contained weak and stressed phyllite rock, allowing machines to achieve world record rates. When conditions get tough, the McNally Support System stands up to the challenge.
Watch McNally slats contain severe rock bursting in the tunnel crown.
Whether you are in the planning phase of tunnel construction or about to bid on a project, our engineers can help you identify the ideal ground support solution to achieve your objectives. For more information, complete our online inquiry form or contact your nearest Robbins location.