Question 9 of 23: Installed-Capacity Utilization, Sequencing and Sizing

Question 1.9: Installed-Capacity Utilization, Sequencing and Sizing (4.44 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

% Utilization. Utilization is the fraction of AVAILABLE (mechanically ready) time that an item of equipment or plant is actually productively engaged, distinct from mechanical/physical AVAILABILITY (the fraction of CALENDAR time it is not down for maintenance/repair): Utilization = Operating hours / Available hours, while Availability = Available hours / Calendar hours. (a) Trucks and shovels: utilization is measured from dispatch-system cycle data as loaded-and-hauling time over total available shift time, net of queueing, shift-change and weather delay. (b) Underground roof bolters: utilization is bolting time over the heading's available face time, constrained by ground-support cycle sequencing with drilling/blasting/mucking in the same heading. (c) Float cell tanks: utilization is the fraction of installed cell VOLUME actually engaged in active flotation (aerated, at design pulp level) versus idle/standby capacity, which governs whether the circuit's nameplate residence time is actually being delivered. (d) Tailings pipelines: utilization is pumped hours over available hours, constrained by line availability (wear, plugging) and by the tailings dam's own deposition schedule.

“% use of utilization.” This second, compounded measure asks what fraction of the equipment's THEORETICAL maximum output (its rated capacity run continuously) is actually being realized once availability, utilization AND performance/rate efficiency (e.g. actual tonnes/hour vs. rated tonnes/hour while operating) are all multiplied together — essentially an overall-equipment-effectiveness figure. It is tracked separately from simple utilization because a fleet can show high utilization (busy most of the time) while still under-performing its rated output rate, and only the compounded measure reveals that gap and where to target improvement (more uptime, more operating hours, or faster operating rate).

Sequencing and sizing. (a) Open-pit sinking cuts are sized and sequenced to maintain minimum operating widths for the truck/shovel fleet on each bench while advancing the pit toward its ultimate design limit at a rate that keeps waste stripping ahead of ore exposure — sizing driven by equipment turning radius and blast-pattern geometry, sequencing driven by the pushback schedule. (b) Underground conventional-caving development headings are sized to the permanent haulage/ventilation cross-section required for the LIFE of the level (larger, one-time cost) and sequenced ahead of production undercutting so that extraction and drawpoint infrastructure is fully established before cave initiation, since headings cannot easily be re-driven once caving begins above them. (c) Tailings (paste/rock) fill in closely isolated stopes is sized to the stope void itself (fill volume matched to extracted volume, plus shrinkage allowance) and sequenced stope-by-stope immediately behind extraction so that adjacent stopes gain the fill's structural support before being mined, with curing time between placement and adjacent extraction an explicit scheduling constraint absent from the open-pit or caving cases.