BULLFLEX® Hoses ensure the safe and flexible Rehabilitation of a Conveyor Tunnel at the Bingham Canyon Mine

Kennecott Utah Copper (KUC) is a mining subsidiary of the global company Rio Tinto. At the Bingham Canyon Mine near Salt Lake City, Utah, KUC has been extracting gold, silver, copper and molybdenum in an open pit mine that will soon be expanded to include underground operations.

The approx. 4.6km (15,000ft) long and 6.4m (21ft) high C6 conveyor tunnel was constructed in 1959 and includes a belt conveyor for transporting extracted ore. A portion of the tunnel leads through a fault zone, the Fortuna fault, where numerous rehabilitation efforts were undertaken prior to 2014.

At the beginning of 2014, progressive damage to the tunnel support was observed that was caused by overstressing due to movements in the surrounding rock mass. Spalled concrete and shotcrete was observed in the steel sets embedded in concrete lining that had been installed as initial support for the tunnel.

Since a portion of the conveyor tunnel could no longer be inspected and maintained, access between the pit portal and the Fortuna fault zone area had to be restricted. This resulted in a critical economic and safety-related risk to the operation of the entire mine.

Under enormous time pressure, the companies involved in the project developed a design concept for the sustainable rehabilitation and strengthening of the tunnel in the fault zone area with the support of DSI Underground Systems. The concept had to take the limited space conditions into account and ensure the uninterrupted operation of the conveyor belt.

Furthermore, ongoing movements of the tunnel in the fault area due to mining-induced deformations required a yielding roof support system that was simple and easy to install.

For this purpose, a yielding support system consisting of TH Steel Sets was used in combination with a prefabricated Type BULLFLEX® Roof Support Backfilling System. The single sections of the TH Sets were bent to the corresponding profiles at DSI’s plant in Louisville on the shortest possible notice. The single sections were connected by yielding locks to accommodate consecutive deformation and yielding in the fault zone area.

Installation in the tunnel was accomplished using a monorail based, elevated work deck to minimize the impact of the installation procedure on the conveyor belt operation. The Type TH-25 and TH-29 profiles and locks were assembled outside the tunnel and transported underground using a jig crane developed especially for this project. Following the installation of the complete TH rings, the 320mm Ø BULLFLEX® Hoses were placed in the gap between the TH profile ring and the excavation surface and were injected with a ready-mix grout.

The BULLFLEX® fabric permits the induction of an active, pre-defined load into the excavation perimeter while maintaining a controlled residual load. The combination of TH profiles and BULLFLEX® Hoses provided a flexible and incremental ground support rehabilitation of the fault zone in the C6 conveyor tunnel with a minimum impact on critical operations. Furthermore, DSI  supplied Type FS Friction Bolts, OMEGA-BOLT® Expandable Friction Bolts and mesh.

Owner

Kennecott Utah Copper, USA

General Contractor

Cementation USA Inc., USA

Consulting

Gall Zeidler Consultants, USA; BuM Beton- und Monierbau Herne, Germany


DSI Unit

DSI Underground Systems Inc., USA

DSI Scope

Design, production, supply, engineering services, technical support

DSI Products

Type TH-25 and TH-29 Profiles, 320mm Ø BULLFLEX® Hoses, Type FS Friction Bolts, OMEGA-BOLT® Expandable Friction Bolts, mesh

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