Dewatering Dike Construction and Grouting at the Meadowbank Mine, Northern Canada

Jet grouting and cementitious permeation grouting was carried out as part of the construction of a series of dikes within Second and Third Portage Lakes at Agnico Eagle’s Meadowbank Mine in Nunavut, Canada. The dikes consist of broad rockfill shells, granular filters, and a central low permeability element. The dikes were constructed to permit dewatering of the isolated portions of the lakes to expose areas for development and extraction of ore from open pits. The low permeability elements are comprised of a combination of soil-bentonite and/or cement soil-bentonite cut-off walls that were excavated using slurry trench technology through the granular filters to bedrock or into a dense foundation soil. In deeper portions, where the cut-off wall did not reach bedrock, jet grouting was carried out between the base of the cut-off wall and the bedrock surface. Grouting of the shallow bedrock and the interface between the bedrock and the base of the cut-off wall and/or jet grout columns was then carried out. This paper describes the techniques used for dike construction with emphasis on the treatment of materials left in place beneath the constructed cut-off wall through jet grouting, along with techniques used for permeation grouting of the shallow bedrock and the interface between bedrock and the base of the cut-off wall and/or jet grout wall (i.e., the contact zone). As the earthworks component of the construction was carried out during the short, open water season of each summer, the grouting works were carried out through the winter and shoulder seasons. For this, a significant level of winterization for all equipment had to be employed. The constraints imposed by the necessity of carrying out permeation grouting operations through the Canadian Arctic winter also led to the development of a novel approach to sealing the contact zone. Steel casings were installed through the cut-off wall and jet grout columns to bedrock, and the underlying bedrock drilled and grouted through the bottom of the casings. The casings were then perforated with a casing perforator tool and the contact zone sealed. Based on the successful dewatering and on-going performance of the dikes, the construction and grouting techniques employed are now considered as viable methods in the Canadian Arctic environment. The successful completion of these works would not have been possible without collaboration between the owner, the contractor and the designer.