Optimum scraper load time and fleet size for minimum emissions

Scrapers are commonly used in road construction, site formation, other earthmoving and surface mining operations. It is known that loading a scraper to capacity may not be best in terms of unit operational cost, because the load-growth curve for a scraper is nonlinear - the loading rate decreases with load time. However, there is no published research considering the effect of load time and fleet size on unit emissions, and what the corresponding optimal load time and fleet size might be. This paper shows that the optimum scraper load time for unit emissions may be the same or slightly less than that for unit cost depending on the scraper type and operation, while the optimum fleet size in terms of minimum unit emissions, is slightly higher than or the same as that in terms of minimum unit cost. Cost-load-time, emissions-load-time and hauling characteristics, particular for different equipment and operations, influence the conclusion. For practice purposes, it could be said that the optimal unit cost and unit emissions solutions essentially coincide. Case study site data, in conjunction with a scraper operational analysis, are used to demonstrate the optima. Both push-pull scrapers and push-loaded scrapers are considered.