Evaluating the economics of constructing mine haul roads using Portland cement stabilization- a case study at Lumwana Mine

Abstract

Surface mine operations engage in various strategies to optimise efficiency and productivity. The efficiency and productivity aspect of such operations aims to deliver the maximum amount of mined tonnes out of the open-pit using minimum resources. Efficiency and productivity entail that the means of conveying the material mined out of the open-pit must be at their best. In turn, equipment used in mining must be available in a good state. Furthermore, the road network and the bench conditions where such equipment operates in must offer minimum resistance for efficient utilisation. In this study, a means of improving the mine haul road condition was examined in which a ramp section at Barrick’s Lumwana Mine in North Western Zambia was stabilised with Portland cement to make it competent with an extended life span. The 300 m of Portland cement stabilised ramp section provided a common overlap of information before and after stabilisation. The information was then used as input for this study. The ramp was observed for data collection over six months, from June 2020 to December 2020. MaxMine, an independent fleet management and optimisation system, was used to collect truck-related information such as speed, time through the section, distance travelled, entry speed, the payload in tonnes, fuel consumption, and surface smoothness of the haul road section. An analysis of this information was able to deduce gains made in fuel usage, truck loaded haul and empty speeds, payload, and haul road smoothness. Information on the construction costs and other input parameters related to haul road maintenance was consolidated from the mine’s project office and used as input data. The research study deduced that cement stabilisation delivered value in the productivity and efficiency of the mine operation as there was a 12% increase in the haulage speed of loaded trucks and a 45% increase in the empty return leg. iv Even though the maximum allowable empty truck speed is 50 km/h on the mine haul roads, going down the ramp is restricted to 30 km/h and the recorded speed in the study of 34 km/h showed that a smooth ramp can be a source of safety violations. The mine has since installed a fleet management system to monitor and manage speed violations and invested in simulator training for its operators to ensure they drive the trucks within safe allowable speed limits using installed systems on the haul trucks such as the speed retarder and cruise controls. There was a 10% reduction in fuel consumption on the loaded haul and 14% on the empty return. There was also a corresponding payload increase of 5% from 243 tonnes to 255 tonnes for the review period. The increase in payload was within the capacity of the tyres to handle and had no negative impact on tyre life as the 53/80R63 tyres fitted on these trucks can handle more than 255 tonnes of payload. It is the same tyre specification used on a Hitachi 5000AC-3 dump truck that carries a nominal payload of 296 tonnes The ramp section in the research study delivered an overall value gain of over $306,000 despite incurring additional road construction costs of 13% above the normal. The additional construction costs were offset by the gains made on reduced haul road maintenance costs, which were reduced by 99.5%. Other gains made were on fuel consumption and truck maintenance through hours saved from truck speeds/cycle time gains.