Strongman mine, a coal mine located north of Greymouth, West Coast, was historically an underground mine (operating since the late 1930’s). It gradually transitioned into open pit mining from the early 2000’s.
Strongman Mine is located in an extreme environment. The landscape is steep and at a high altitude, with the offices located 600 meters above sea level. Annual rainfall exceeds 6 metres, with snowfall a regular occurrence during the winter months. Haul roads, pit walls, overburden disposal sites, and daily life on the mine are made challenging due to these environmental conditions. Environmental issues such as water management and ground control are important aspects in the pristine environment that surrounds Strongman. Initiatives such as redirecting mine water into underground mine workings have been used to naturally filter suspended sediment, without having to use chemical flocculants. Ground control with regards to rehabilitation of the pits and overburden disposal sites for stability, longevity and overall safety was managed professionally, with regular input from the West Coast Regional Council and Department of Conservation. Historic and more recent mining activities onsite had resulted in coal fires burning in the underground workings. This smouldering underground fire has been burning in the Strongman Mine since 1996. The underground fire raged for over 17 years, despite Solid Energy's best efforts to extinguish it.
GEOTECH Ground Engineering took over the site from 2010 -2015 and was successful in a significant reduction of the fire liabilities as well as removing additional coking coal. These fires were constantly monitored and constrained. The introduction of “stowing” onsite was used to infill underground workings with saturated crusher dust, and pressure injection of bentonite clay into voids was used to reduce air flow to the fires, essentially limiting their fuel.
