The Diavik mine is operated by Diavik Diamond Mines Inc., a member of the Rio Tinto Group, and is located approximately 220 kilometers south of the Arctic Circle and 300 kilometers by air from Yellowknife, the territorial capital.
A deep cut-off wall was required for the 2.2 km perimeter dike so that the fourth kimberlite pipe, designated A21 and located under the waters of Lac de Gras, can be open-pit mined. A combination of different foundation engineering techniques was required to construct the proposed cut-off wall structure safely, efficiently, and within environmental regulatory limits.
The location of the mine presented special challenges, enabling works only between May and October. Logistics was another major challenge, as large transports are only possible during an eight week window during the winter when the ice road to the mine is open. As a result, the project had to be completed in two stages in 2016 and 2017.
The foundation works started with the vibro densification of the filled dike body along the proposed cut-off wall alignment. The actual bedrock below the filled dike body was sealed with a grout curtain (drilling, water pressure testing and grouting) to a depth of nearly 60m. The final Cutter-Soil-Mixing (CSM) cutoff wall had to be installed through the densified dike into the geological till-material embedded above the bedrock. More than 23,000m pre-drilling in advance of the CSM works was executed to ensure embedment of the 23m deep CSM cut-off wall into the till material.
More than 19,000m² of wall were installed along the dike perimeter utilizing this foundation technique, whereas the shallower connection points at each end of the dike were open excavated and filled with similar slurry material.