A key process in open-pit mining operations is loading. During this process loading equipment (excavators, shovels, etc.) fill-up the haul trucks with material for movement from the pit to the surface. It is important that the mine scheduling and dispatch system is efficient so that the loading equipment and haul trucks can be optimally utilized – leading to maintaining or improving mine production targets.
Truck saturation factor is defined as the percentage of time that the loading equipment is actually working (loading a haul truck) and ranges from 0% to 100%. A low truck saturation factor indicates that the loading equipment is waiting for haul trucks (under-trucked) and a high truck saturation factor indicates that the haul trucks may be potentially queuing at the loading equipment (over-trucked).
Truck saturation factor and hang time
Essentially truck saturation factor is the opposite of loading equipment hang time (the time the loading equipment is waiting for haul trucks). Truck saturation factor focuses on work done whereas hang time focuses on the time the loading equipment is not working. As a result it would be expected that with a low truck saturation factor, hang time would be high and with a high truck saturation factor, hang time would be low.
Truck saturation factor and productivity
The productivity of the loading equipment is generally equivalent to the truck saturation factor multiplied by the instantaneous productivity (referred to as loading rate). As a result it would be expected that as truck saturation factor increases productivity increases to the instantaneous productivity.
Truck saturation factor is calculated using the following equation:
Working time is the time the loading time equipment was loading haul trucks – the time the haul trucks take to get into position at the loading area (referred to as spotting time) may also be included in this as the loading equipment cannot be used during this time.
Utilised time is the time the loading equipment was in operation (inclusive of working time and production delays).
The determination of truck saturation factor may vary from mine to mine based on mine specific time models and definitions.
Truck saturation factor identifies if particular loading equipment are being under-trucked or over-trucked. Based on this information relevant changes can be made to improve scheduling and dispatching – resulting in improved utilisation of the loading equipment and haul trucks.