AbstractsEarth & Environmental Science

Traditionally, earthmoving and like operations have been organised based on a minimum unit cost criterion. However, there is an increasing awareness of the need to reduce carbon emissions due to their negative environmental impacts and the growing presence of carbon trading schemes and carbon taxes. This thesis examines earthmoving and like operations, including loader/excavator-truck and dozer-scraper operations, under two criteria – minimum emissions per production (unit emissions) and minimum cost per production (unit cost), and compares the optima for these criteria. Queuing theory is used for the theoretical evaluation of production for varying operation parameters. Variables considered in the analyses performed include equipment heterogeneity, payload, truck size, haul grade, and travel and load times. Truck dispatching is performed through the linear programming method and the effect of truck allocation on unit emissions and unit costs is established. It is demonstrated theoretically that the optima with respect to unit cost and unit emissions coincide in excavator/loader-truck operations, and this coincidence is invariant with changing operation parameters. To support the theoretical result, data from extensive field studies are used, including time and production measurements, and fuel burn data and its conversion to idling and non-idling emissions. Sensitivity analyses on the underlying parameters also support the conclusion. This thesis also 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. Yet 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. It is concluded that the traditional way of undertaking earthmoving operations to give minimum unit costs will also result in minimum unit emissions. And that different configurations will lead to unnecessary emissions. In addition, the existing linearprogramming dispatching solution, based on minimising truck numbers and unit costs, accordingly impacts the environment the least in terms of emissions. It is important to know that the most environmentally friendly approach is also the most economical because this will reassure contractors who are concerned about environmental policy impacts on financial operations.