Truck-shovel optimization accounting for cost, safety, and operational practice

CIM Bulletin, Vol. 98, No. 1090, 2005
C.O. Aksoy, H. Kose, T. Malli, K. Ozfirat, A. Gonen, and S. Gurgen
Abstract The file is a zipped PDF document.Thirty per cent of the electrical energy in Turkey is provided by coal-fired thermoelectric power plants. Five per cent of the demand is met by the Soma power plant’s six 165 MW generators. The plant is fed by lignite from open pit and underground mines in the Soma region that are operated by the government. With a nationalized mining policy in place, recently no investment has been made at these mines, as mining activity is generally considered by the government to be a risky and costly venture. To be competitive in a globalized marketplace, the mines in the Soma region aim to minimize their operating expenses. In the study variations, the bench height was set at 10 m or 15 m, with blasthole diameters at 152 mm. In order to examine the effect of road grade on unit cost, ramp slopes were set at 8% or 10%. While low slope angles increase unit cost, high slope angles jeopardize safety. The general pit slope and bench slope angles were assumed to be 40º and 75º, respectively, based on safe practice in this region.In the analysis, shovels of a range of capacities from 1.9 to 17 m3 were evaluated. Under present conditions, open pit mines are economical up to overburden ratios of 1:30. It was assumed that the overburden ratio in the region of study was 1:10 t/m3, with annual production varying from 1.5 to 2.0 million tons. This led to the identification of an annual stripping requirement ranging from 5 to 20 million cubic metres of overburden. Kose et al. (2005) stated that pit quarry mining with low bench heights and large blasthole diameters reduced the overall unit cost, whereas hillside quarry mining required both the bench height and the hole diameter to be large to reduce the unit cost.In selecting mobile mining equipment, factors including availability, useful economic life, maintenance and operating costs, and spare parts availability are considered. Given these factors, trucks and shovels with different capacities are selected. Optimizing equipment for pit and hillside quarry cases where 8% and 10% ramps commonly in use were examined, the effect of other mining activities, such as drilling and blasting, on unit cost were considered. In principle, 20 m to 25 m high benches should be economical for downhill haulage, and 7 m to 10 m low benches economical for uphill haulage. However, practice of both mining styles favours 10 m to 15 m bench heights.  Hence, the analysis here was carried out with the field experience bench height range. In the study, a truck-shovel optimization was based on the movement of 5 to 20 million cubic metres (in 2.5 million cubic metres increments) of overburden stripping at the Eynez open pit mine in the Soma region of Turkey. The outcome showed that low-capacity shovels were unfavourable due to high production expectations. High-capacity shovels were also unfavourable due to health and safety issues causing high instances of impact vibration on trucks during the loading cycle and a decrease in foreseeable unit lifetimes. The number of shovel passes required to load a truck ranged from three to six. Trucks with high-capacity bodies were deemed uneconomical due to high investment and operating costs.
Keywords: Optimization, Cost, Drilling, Blasting, Load-haul
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