I've just come back from meetings with people from the mining industry in Canada. I notice that Shotcrete is widely used in underground mining and appears to be regarded as the ground support system of the future.
The opinions that were shared with me suggested that Shotcrete increases production, potentially because mining teams can get in quicker. What normally happens after drilling and blasting is that a minimal team will assess the site for safety. They might have previously used a rock-bolt strategy to stabilise the tunnel surface, but now they can use a bolt and shotcrete strategy, and that delivers a much faster outcome.
Bolt & Mesh Stabilisation Is Time Consuming
The rock bolt procedure involves drilling in a big, long bolt to secure the boulders so that they don't fall and then they'll use mesh to hold the rocks in place. The time taken varies from site to site, but the bolt and mesh process can take quite a while. No production crews can go back in during that time.
Shotcrete is Fast
Shotcrete use boosts productivity because it allows production at the face to continue after a shorter period of time. A machine will spray all the walls with quick-set concrete. After it is dry, production crews can go back in to do their work. The time saved represents a boost to productivity and savings in labour costs.
Shotcrete Makes Movement Visible
Shotcrete also has the added benefit of making any rock movement immediately visible. Teams can see a two-millimetre crack appear, and they will know they have some rock movement. It isn't as easy to see those small movements with the bolt and mesh surface stabilisation strategy.
Shotcrete Requires Less Long-term Maintenance
One problem with the bolt and mesh strategy is that the mesh corrodes and this creates the need for ongoing maintenance. Shotcrete and polypropylene fibres do not corrode, so they do not need as much ongoing maintenance.
The use of automation in mining is allowing for deeper drilling. In Canada, they are now working at about 2000-3000 metres deep. Temperatures are 60C as they go deeper and the hotter the environment, the more difficult it is for humans to work. This factor is driving the increased use of autonomous machinery in deep hot environments.
Shotcrete Polypropylene Fibres Stronger and Don't Corrode
Polypropylene fibres are being used predominantly in Shotcrete for its mechanical strength coupled with its corrosion resistance. Steel by itself is stronger than polypropylene but steel corrodes. There's something about the water that forms or gathers around these geological areas where they find commodities that is corrosive. You'll find acidic water in areas where there's gold, copper, zinc forming in the ground. That's why the polypropylene fibre is more suitable than metal fibre for surface reinforcement in underground mines.
My main takeaway from Canada was that Shotcrete is here to stay because it offers significant production and safety benefits for mining companies. Having a submersible dewatering pump that is designed to handle Shotcrete fibre is going to be an increasingly important part of the picture.