Evaluation and mapping of corrosion in a western USA underground metal mine — year one preliminary results

Abstract

Corrosion of ground support can lead to falls of ground, posing a significant risk to miner safety. To address this problem, the Spokane Mining Research Division of the National Institute for Occupational Safety and Health is investigating ground support corrosion at the Greens Creek mine, located near Juneau, Alaska, United States of America. Field and laboratory studies include surveys of weld-wire mesh corrosion, rock mass conductivity measurements, and sample analyses using a scanning electron microscope, energy dispersive spectrometry, and Fourier transform infrared spectrometry. Current field studies demonstrate a correlation of rock mass conductivity to the degree of weld-wire mesh corrosion and the relationship of ground conductivity surveys to support corrosion potential. Laboratory analyses of mine samples identify the presence of sulphate, which is a determinant for sulphate reducing bacteria activity. Identification of sulphate reducing bacteria (SRB) would provide evidence for microbial influenced corrosion in this mine. Ongoing research is evaluating methods of SRB inhibition. These results provide engineers with a means to map corrosion potential of the rock mass, and identify a number of paths for design of focused mitigation efforts for problem areas.

Analysis of in situ and laboratory corrosion coupons

“…In order to investigate the viability of using these guidelines in mining, rock mass resistivity was measured using a Wenner Array (ASTM International 2005). The electrodes were installed by drilling four holes with 10.14 cm (4 in) spacing and inserting 7.62 cm (3 in) stainless steel construction screws as electrodes (Chambers et al 2017). With the electrodes in place, a resistivity instrument measured both the current and voltage, calculating the resistivity using the following relationship:…”