The Det’on Cho Nahanni Construction (DCN) Ltd. won the $11.6 million contract for Interim Underground Stabilization in August 2014 through a competitive process. Under the two-year contract, DCN engaged in a design-build contract with support from a full range of professional consultants and contractor services.
About the Project
The work included stabilization of old mining stopes, some of which consisted of caverns the size of 12-storey buildings. DCN assessed the empty chambers, determined the requirements necessary to stabilize these chambers, and developed the plan to backfill the voids with paste material. The backfill paste was created with reclaimed tailings allowing for an on-site source of material, and reducing the need for trucked in aggregate. This paste was used in the stabilization of each underground chamber and reduced further degradation of both the crown/sill and rib pillars. Paste material was delivered to each underground stope with use of boreholes from the surface. A Nahanni-designed quality control program included the use of a wireless network of live-feed cameras as well as laser cavity scans where necessary. This technology was implemented to ensure the backfill activities were completed as designed.
The Giant Mine site is located within the city limits of Yellowknife, the capital of the Northwest Territories and home to almost 20,000 people. Arsenic trioxide dust that accumulated over 46 years of mining activity at the site was pumped underground for final storage. These areas needed to be stabilized to ensure chambers are kept intact to protect the environment and nearby community. There are significant health and safety considerations that go along with working on the site that include contaminants, silica dust, unstable ground, and dated supporting structures. There is a care and maintenance operator at the mine and often several other contractors working at the site. There is a significant amount of coordination necessary to operate effectively at the site and communication with contractors and on-site staff was important for project success. Timely supply of equipment, materials, and supplies is essential to ensure that DCN meet our scheduled commitments. Being situated in a northern location, Giant Mine exists in a climate that creates limitations and constraints in performing the paste production and delivery. The site is regulated by the Mackenzie Valley Land and Water Board and a water license is in place for the site that must be adhered to. This project involves filling the required voids while keeping other parts of the mine open and unhindered by paste. This is an operation that is complicated by drilling, monitoring, and underground distribution logistics on a busy legacy mine site.