Abstract:

A new wireless method for data collection and automation was introduced at BHP’s Jansen mine. The large potash resources of northern Saskatchewan (Canada) are among the richest in the world but are notoriously difficult to extract. The deposits of this region are typically located at depths between 900 and 1000 m from the ground surface. The construction and sustained operation of these mines are closely managed due to the significant risks of flooding as the potash deposits are located below a water-bearing formation: the Blairmore formation, a sand-shale-clay-siltstone layer, at a depth of 500 m is a water rich formation that increases the risk of flooding.

Shaft sinking was performed with a shaft boring roadheader (SBR) digging through pre-frozen ground. During shaft sinking, a temporary waterproof liner was installed. Upon reaching the potash deposit, the final liner was built from the bottom up by pouring consecutive sections of concrete, encasing a continuous welded steel liner that waterproofs the shafts. This unique construction method leaves a narrow range of safety factors on the custom high-strength concrete used for structural integrity. Consequently, accurate strength measurements were obtained by curing concrete samples submitted to the specific temperature profiles that the poured concrete was subjected to. The system introduced in this project measures temperatures with embedded thermistors and relays the readings in real-time to the top of the shaft over a LoRa network. From there an automated control system retrieves readings in real-time. The control system outputs the readings as setpoints to series of cure tanks with both heating and cooling to match the temperatures of the samples within 2°C of that of the poured concrete. Proper temperature matching was confirmed by introducing a temperature sensor in specific one cylinder for each tank. In addition to the data obtained from break tests, a custom-built visualization tool computes the maturity curves for each section and handles numerous alarm types to ensure that temperatures rise at a specific rate, that it never exceeds specific thresholds, that there are no significant temperature gradients and that sections behave accordingly to the models. This novel method allowed the constructor to complete liner construction in 2022. The internet-of-things methods introduced in this project allowed the integration of structural health monitoring for the long-term maintenance of the shafts. This new method is applicable for linear structures such as tunnels and bridges in which access might be difficult to collect temperature measurements or samples.

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Stéphane-Éric Thivierge