2153 Panel 2 3.3 Material efficiency and quality Another notable result was the reduction in shotcrete rebound and overall material waste. With the wet-mix, fiber-reinforced shotcrete and improved spraying technique, rebound (the portion of material that does not adhere and falls to the floor) was observed to be around 10–15% of volume applied. This is an improvement from the ~20–25% rebound measured previously with the dry-mix, mesh-reinforced process. Over the course of the trial, this efficiency saved many cubic meters of shotcrete material and reduced the frequency of mucking out rebound debris. Additionally, because the accelerator used was alkali-free, there was no formation of soluble alkali salt dust on the tunnel walls or floor, which is typically a byproduct of older accelerator chemistry (Allison et al., 2010). This contributed to better long-term shotcrete quality (alkali-free accelerators are known to improve the durability of shotcrete by avoiding alkali-related strength loss) and a safer work environment for the crew (less caustic dust exposure). The wet-batching process ensured more uniform mix quality, which was reflected in consistent strength results and layer thickness. During the trial, the actual applied shotcrete thickness averaged ~60 mm with ICS (target was 50 mm minimum). This uniformity gave confidence that the design thickness was achieved with less variability than before, when hand-spraying and dry mix often led to uneven coverage. Nozzling crew feedback also indicated that the pump and robotic sprayer combination reduced fatigue and allowed better control of placement, further improving quality. 3.4 Operational and logistical impacts The switch to an in-cycle process had implications for mine logistics, generally positive. By adopting wet-mix shotcrete prepared on-site, the mine reduced its dependency on transporting large quantities of bagged premix and accelerator to the face for each round. Instead, bulk materials (cement, admixtures, fiber) were stockpiled near the portal or underground stockyard and mixed as needed. The trial required close coordination: the shotcrete crew had to be ready to mobilize as soon as mucking finished. Initially, there were minor challenges in timing and communication, for instance, one round had to be resprayed due to a long delay that caused the first batch to set in the hose. These issues were ironed out by establishing clear standard operating procedures and communication via the mine’s two-way radio system
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