Macassa Tailings – Shear Key Construction
Single Auger Soil Mixing
Macassa Mine Complex
Kirkland Lake, Ontario
Significant Project Features:
• In Situ Soil Mixing (ISSM) to a maximum depth of 41.9 feet (12.8 m) below ground surface.
• Geotechnical improvement of low strength tailings material with Portland cement to facilitate future tailings dam expansion and to improve the factor of safety of the existing dam.
• Excavation under slurry to remove organics layer prior to soil mixing operations.
Project Background:
GSI installed soil-cement shear key elements to support dam reinforcement at two locations (Upper Dam B and Lower Dam E) using In Situ Soil Mixing (ISSM) with a large diameter single auger soil mixing drill. GSI completed the ground improvement of low-strength tailings materials on this project using a Delmag RH-18 track-mounted auger drill rig to mix a General Use (GU) Portland cement and water grout into the soil.
At the Upper Dam B location, pre-excavation was used to remove unsuitable organic material (peat) prior to soil mixing. Excavation was performed at each key location until the organic material was removed and the clay layer beneath it was reached. Backfill material in pre-excavated locations consisted of any segregated inorganic soils from the excavation along with imported granular material provided by the owner.
Description of Work:
• Installation, sonic core drilling and excavation/testing of six test columns.
• Sonic Core drilling of eight production columns.
• Installation of 228 eight-and-a-half foot diameter soil mixed columns constituting 76 shear key elements across 6 zones (5 zones in Upper Dam B and 1 zone in Lower Dam E).
• Maximum mix depth from ground surface of 41.9 feet (12.8 m).
• 340,761 cubic feet (9,649 cubic metres) of soil stabilized with 5,022 tons (4,556 metric tonnes) of Portland cement.
• Average UCS of stabilized soil was 1,017 pounds per square inch (psi, 7.01 MPa) after 28 days of curing.
• Work was completed over 11 weeks, including 3 weeks of setup / teardown.
Key Project Objectives
• Ensure that the unsuitable organics layer had been removed from the treatment zone prior to treatment
with Portland Cement.
• Confirm that the strength of the composite treatment zones was greater than the required design strength of 208 psi.
Project Challenges:
• Long turnaround time for cement deliveries.
• Working on a rugged, variable work platform.
• Minor delays from weather conditions and equipment malfunctions.
• Heavy and frequent mine related traffic within close proximity of soil mix operations (especially for Lower Dam E).
• Hard drilling conditions through the road surface in the northwest region of Lower Dam E.
