Heath Steele Mine — Auxiliary Spillway

Heath Steele, near Wayerton, is a closed mine with a tailings facility that still has to be maintained. The new auxiliary spillway is cut through rock near both the Main Dam and the Internal Dam, with a hard limit of 25 mm/s within a metre of either.

The usual way to design for a limit like that is a textbook attenuation formula. We didn’t. The blast designs use constants regressed from the measured vibration of 30 monitored blasts at the Caribou tailings dam raise — a directly comparable New Brunswick site — and they design to the 95% upper prediction bound of that data, not its average. The blasting plan was independently reviewed before work began, and a trigger-action plan sets out exactly what happens at 15, 20 and 25 mm/s.

Production holes are loaded with bulk emulsion from our 1,800 kg mini pumper, metered hole by hole. A fully coupled column with a known mass in every hole is what makes charge per delay — and therefore vibration — predictable. It is also what pulls the floor: the rock is shallow and there is no subdrill near the concrete, and pumped emulsion puts full energy at the toe of the hole where packaged product, in the same pattern and hole size, would leave it standing.

Through the first 15 blasts, the highest reading at the dam was 4.3 mm/s, and every blast stayed in the normal operating band.