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Final Wall Control: Understanding and Applying the Half-Cast Factor in Open Pit Mining In open pit mining, achieving a stable and geotechnically compliant final wall depends heavily on how effectively blasting energy is controlled along the designed slope. One of the key quality control measures in this process is the Half-Cast Factor (HCF), a simple yet powerful indicator of how well the pre-split or final wall blast performed. The methodology to calculate the Half-Cast Factor involves measuring the number of visible half-casts (pre-split barrels) along a given section of the final wall and dividing it by the total number of pre-split holes drilled in that section. For instance, if 20 holes were drilled and 15 half-casts are visible, the resulting HCF is 0.75 (or 75%). Mathematically: "Half-Cast Factor"="Length of visible half-casts" /"Total length of pre-split holes" X 100% A high Half-Cast Factor (≥ 0.8) indicates that the blast energy was well confined between the pre-split holes, maintaining a clean separation between the final wall and the blasted rock mass. Conversely, a low HCF (< 0.6) suggests excessive energy or poor coupling, leading to overbreak, crest damage, and loss of wall integrity (Jeroen van Eldert, 2018) Carrying out this exercise routinely is critical because it allows mining and geotechnical teams to: ✅ Assess final wall stability by quantifying blast-induced damage. ✅ Calibrate blast designs, adjusting burden, spacing, and charge per hole for improved wall control. ✅ Reduce future remediation costs associated with scaling, rock bolting, or catchment redesign. ✅ Support slope monitoring programs by correlating Half-Cast Factor results with radar or prism movement trends. The photo below shows a well-defined pre-split wall, with visible half-casts demonstrating good control along the final face, a sign of precise drilling, accurate timing, and optimal charge confinement. Ultimately, monitoring the Half-Cast Factor transforms wall control from a visual inspection to a quantitative performance metric, ensuring safer, steeper, and more economical slopes, the true foundation of sustainable open pit operations

Figure 1 shows a short-term execution plan: a task-level schedule by block with a matching Gantt chart for activities like block prep, drilling, blasting, and loading/hauling across specific dates and per cent complete. This is the actionable weekly plan that converts quarterly intentions into sequenced tasks, revealing whether upstream quarterly sequencing is feasible once real equipment hours, benches, and inter block dependencies are honoured. Figure 1: Block Sequencing Why sequencing matters now • The order of drilling–blasting–hauling across blocks determines whether access to the next ore block opens on time, directly affecting short-term cash flow and NPV contributions of the quarter. If drilling slips on the lead block, blasting and ore exposure slip, starving the plant and eroding NPV. • Short-term plans must respect pit precedence, geotechnical widths, and fleet capacity; the table’s “days complete/remaining” and “per cent complete” columns are the control points to keep exposed ore ahead of the shovel, preventing production delays. Sustainable ore access in weekly plans • Use the execution plan to enforce a minimum “exposed ore” buffer: ensure each ore block’s loading window begins only after preceding waste and prep tasks clear access, and maintain a rolling stock/exposure KPI for the next 1–2 weeks. This operationally enforces the “minimum exposed ore" concept. • Sequence pushbacks so that waste removal tasks in the Gantt precede high-grade ore starts by several days, keeping pit geometry regular and avoiding re handles; this short-term discipline is what sustains long-term access. Leveraging market conditions • When prices are high, front-load high-grade blocks in the near-term chart by accelerating drilling and blasting earlier and allocating more shovel hours, while shifting some low-grade or waste to night shifts or subsequent weeks; when prices weaken, delay lower-margin ore or feed from stockpiles. This dynamic cutoff and rate adjustment enhance quarter NPV. • Scenario test the next four weeks against price bands: re-sequence blocks and update the Gantt to schedule capital-intensive moves (e.g., additional shovel or contractor drill) only in favourable windows. Adaptive plans can outperform static ones significantly. How the figure should be used • Validate quarterly plan: if the Gantt shows overlapping haul or drill windows causing resource conflicts, it is an early signal that the quarterly sequencing was unrealistic; fix at the execution plan first because this is where actions occur. • Maintain leading indicators: track “per cent complete” on critical path blocks and a daily “days of exposed ore ahead” metric; if exposure drops below target, reassign drills or add a blast to protect mill feed continuity. Where to invest effort • Prioritise execution scheduling quality: tighten activity durations, resource calendars, and inter-block links so the plan is feasible and resilient; poor execution plans translate directly to downtime and lost margin. • Build a rolling 4–6 week look ahead tied to quarterly milestones: the weekly Gantt is updated daily, but always anchored to opening the next pushback’s ore blocks on time to preserve sustainable access and market timing benefits

Mine-to-Design Reconciliation: Turning Data into Safer, Smarter Mining At the heart of effective open-pit operations lies one critical question: are we mining to design? Using monthly survey data(topography/pit-scan) imported into GEM4D, this reconciliation process compared the pushback design with the as-mined surfaces to evaluate compliance and identify areas requiring corrective action. A color-coded 3D analysis of variances of ±2.5 metres between design and actual pit surfaces is used whereby: • Over-breaks (+2.5 m, blue zones) indicates areas mined beyond design limits. This compromises wall stability and increases the risk of rockfall. • Under-breaks (-2.5 m, red zones) highlight frozen toes and incomplete blasting, often caused by (short drill holes, incorrect burden and spacing, weak bottom charge and inadequate stemming), which also reduce bench catchment effectiveness and safety. By mapping these deviations, the team is able to pinpoint visually where design adherence is lost, assess geotechnical risk, and plan corrective measures such as targeted re-blasting and slope reconditioning. Continuous monitoring through survey updates and movement radar ensures that compromised areas are flagged in the pit hazard plan, reinforcing both safety and design discipline. This exercise demonstrates that mine-to-design reconciliation is not just a compliance check, it’s a powerful feedback loop that improves safety, slope stability, and long-term economic performance. As geological structures and operational realities evolve, frequent design validation keeps open-pit operations aligned, efficient, and resilient.