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 between jumbo operators, loaders, and shotcrete crews. Overall, the development cycle became more streamlined. A previously separate activity (shotcreting much later) was merged into the cycle, which meant one less “stop-start” in the broader development process. As an indirect benefit, the equipment utilization was also improved: the development jumbo could move to the next face or perform other tasks while shotcreting was underway, instead of sitting idle waiting for a previous cycle’s support to finish. The holistic planning of the cycle ensured that each piece of equipment and crew was optimally scheduled. From a cost perspective, the mine analyzed the trial results and found that the cost per advance meter with ICS was slightly reduced (by ~5-8%). The higher cost of the advanced shotcrete mix and continuous presence of a shotcrete crew was offset by the greater advance achieved and the reduction in other support materials (e.g., less mesh, fewer rock bolts in some areas, and lower rework costs). Additionally, improved safety performance (no minor falls of ground in trial headings) can be considered a cost saving by avoiding downtime and incident investigations, though this is harder to quantify. DISCUSSION The successful implementation of in-cycle shotcrete at Inmaculada provides several important insights into both the technical and strategic aspects of accelerating mine development.
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