CIM Bulletin, Vol. 1, No. 2, 2006
J.-F. Lessard and J. Hadjigeorgiou
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In underground mines, material handling systems rely on a network of vertical or steeply inclined ore and waste passes. The design and operation of ore pass systems is often based on past experience, which can be anecdotal and, at times, contradictory in nature. This paper provides quantifiable information on ore pass practice and performance in Quebec underground metalliferous mines. The presented field data were derived during a series of site visits in ten underground mines from 2001 to 2003 (see Table). In order to provide a standard methodology to quantify current practice, an extensive questionnaire was developed. At every site, underground assessments were complemented by data collection (design, engineering, problems encountered, and the success or failure of different interventions to restore flow) and site interviews with key mine personnel from the engineering, production, safety, and training departments. This paper reports the analyses of the collected data and, in particular, design practice, material properties, and, the overall performance of ore and waste pass systems.
Separate ore pass–waste pass systems are the norm in Quebec underground mines. The use of LHDs with large-capacity buckets implies that it is possible to dump large rock fragments in the ore passes. This can be prevented if the mucking crew follows strict guidelines to transfer larger rock fragments for secondary blasting, or by installing well-designed screening equipment (scalpers, grizzlies) at dump points.
The length of the excavation plays an important role in the performance of an ore/waste pass. Longer ore/waste passes have a greater probability of intersecting zones of poor ground and require the development of finger raises resulting in more dump points in the system. Finger raises are often detrimental to the integrity of ore passes. Waste passes are less susceptible than ore passes to problems. In the database, 88% of ore passes longer than 100 m experienced severe problems while only 43% of waste passes experienced wall degradation. This is attributed to operating practices, where waste passes are kept relatively full most of the time. Another explanation is the relative low unit weight of waste rock compared to ore material transferred through the passes.
All mines report some type of flow-related problems, with interlocking hang-ups being more common. Cohesive hang-ups were observed when mining zinc-rich stopes (often referred to as sticky ore) or when the dilution due to the paste fill is high. Although ore pass size is the most important factor influencing material flow, quite often it is the size of the Alimak platform and not engineering considerations that decided the dimensions of an ore pass. Material flow problems also result in ore passes that are not steep enough. It is of interest that ore passes inclined over 70º did not report hang-up problems. The presence of screening infrastructure reduces the occurrence of interlocking arches and mitigates the impact on ore pass walls. Operating ore passes as flowthrough is the norm in most mines in the database. Although this practice results in fewer hang-ups, it also exposes the walls to further damage from impact loads.