Nahanni Construction has been engaged on several projects related to underground stabilization work related to the remediation of Giant Mine in Yellowknife, Northwest Territories, from 2014 through 2022. Several contracts for underground stabilization and backfill projects have been awarded to Nahanni; leading to NCL becoming a key contractor in the Giant Mine Remediation. Throughout this work this unique project has provided the opportunity for Nahanni to become an innovator in the specialized area of underground concrete stabilization.
About the Projects
Initial Works (2014)
Work in 2014 – undertaken as a joint venture operating as Detoncho Nahanni Limited (DCN) – included stabilization of old mining stopes, some of which consisted of caverns the size of 12-storey buildings. Nahanni 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. This technology was implemented to ensure the backfill activities were completed as designed.
C5-09 Stope Complex Stabilization (2018 – 2019)
In 2018 – 2019 Nahanni returned to execute the underground mine backfill for the C5-09 Stope Complex Stabilization at Giant Mine, Yellowknife, NT. This involved deploying a non-segregating paste material, formulated on-site using reclaimed tailings. Nahanni managed the paste design, which included processed tailings, water, binder, and chemical additives. The comprehensive backfill program also included a 10-meter thick Self-Consolidating Concrete (SCC) formulation.
NN2111 – Early Works Drilling (2021-2022)
In 2021 -2022 Nahanni was engaged to lead the Giant Mine Early Works Drilling which involved intricately drilling multiple paste delivery and monitoring boreholes to access complex underground historical mine works. Notably, many of the borehole starts were in challenging areas such as pit bottoms, highwalls, and zones with organic material which required innovative solutions and tactical management of resources to ensure project success.
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 with hazards such as silica dust, arsenic trioxide, unstable ground, and dated supporting structures. There is a care and maintenance operator and often several other contractors working at the mine site, which means a significant amount of coordination is 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 and the associated logistics on-site for delivery and staging were essential to ensure we met 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. The scope of work for stabilization projects included filling the required voids while keeping other parts of the mine open and unhindered by paste. This is an operation that is complicated by challenging drilling, monitoring, historical underground structures, and complex logistics on a busy legacy mine site.