2151 to a significant increase in development footage. The mine recorded an increase from approximately 200 rounds per month to about 232 rounds per month in the trial areas – about 16% more rounds, closely matching the cycle time savings. However, due to other constraints (manpower, blasting schedules, etc.), the net improvement in overall development meters realized was around 8–10%. This is still a substantial productivity gain considering no additional equipment or shifts were added. Figure 1 illustrates the comparison of cycle components before and after ICS. Notably, the formerly time-consuming support stage was largely absorbed into the normal cycle without extension: shotcreting (plus any delayed bolting) was accomplished within the blast re-entry window. The development jumbos and crews could operate more continuously with fewer idle periods waiting for ground support completion. Figure 1 – Development cycle time breakdown per round before and after ICS implementation. The shotcreting stage was moved in-cycle, significantly shortening the delay before the next drill-blast Figure 1 3.2 Early strength development and ground support performance Field tests confirmed that the in-cycle shotcrete mix gained strength rapidly underground, consistent with lab results. Penetrometer measurements and a limited number of early-age core breaks indicated compressive strength on the order of 1-1.5 MPa at 1 hour after spraying, and 3-4 MPa at 3 hours. In contrast, the mine’s previous standard shotcrete (a slower-setting mix with lower accelerator dosage and no fibers) reached only about 0.5 MPa at 1 hour and ~2 MPa at 3 hours. By 24 hours, the ICS mix exceeded 20 MPa, and ultimately attained >40 MPa at 28 days, comparable to the long-term strength of the standard mix. The improved early strength allowed safe re-entry in under 3 hours, as intended, without observed failures. During the trial, no instances of sloughing or collapse were reported in areas that had been shotcreted incycle, whereas historically some headings experienced minor falls of ground in the interval between blasting and the next shift’s shotcreting. The fiber reinforcement proved effective in controlling cracking and enhancing toughness of the liner. Observations showed that even when blasting the subsequent round, the fresh (only a few hours old) shotcrete remained well-adhered and suffered only hairline cracks, but did not dislodge. This indicates it had developed sufficient integrity to withstand blast vibrations and stress relaxation. This performance is significant: it demonstrates that with proper design, an expedited shotcrete can serve as a competent temporary liner, even when subjected to early-age disturbances (Bernard, 2010). Table 4 shows a summary of Early-Age Compressive Strength Results for ICS Shotcrete Panels (MPa).
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