Stability of an abandoned siderite mine: a case study in northern Spain

Bodovalle is an iron carbonate mine located in Gallarta (near Bilbao, northern Spain), which is currently in the closure stage. The deposit was first exploited as an open-pit mine and later as an underground mine. The underground mine currently has 40 large rooms with rib pillars, occupying an area of 2,000m long by 600m wide. Room depth is around 200 m. The main geotechnical incident occurred in the NW1N zone, where an overexploited rib pillar in poor condition was partially removed, leaving a 70-m roof span that eventually collapsed in 1999, resulting in a surface crater measuring 60m in diameter. The collapse was preceded by noises and movements detected outside the mine. The subsidence was improved by means of infilling and monitoring. In 2014, residents living in homes built over the abandoned mine rooms detected very loud noises similar to those of 1999. The article describes a stability review carried out using advanced numerical methods (finite element method and boundary element method) and the geomechanical parameters obtained from a back analysis of the 1999 collapse.