Geotechnical design of underground slate mines

Slate is one of the most important natural materials in Spain, with a potent extractive and processing industry concentrated in the autonomous communities of Galicia, Castile and Leon. Thanks to its resistance to external agents, its impermeability and its excellent cleavability, slate is used as for roofing and tiling. Almost all the active exploitations in our country where this resource is extracted are open pit mines, where the exploitation ratios have nearly reached their economic limit, making it necessary to look for alternatives that will allow the mining works to be continued. Underground mining is a solution that offers low exploitation ratios, with low spoil generation. The room-and-pillar method with barrier pillars is usually applied for the exploitation of slate deposits. There are several factors to be taken into account when designing a mine (economic, logistical, geotechnical, technical, environmental.), especially for an underground mine. This study focuses on the geotechnical design process of a room-and-pillar underground mine, based on the tributary area theory, the analysis of the tensions in the ground with numerical methods and the choice of an appropriate reinforcement in view of the expected instabilities. This explanation is completed with an example of a design that includes the estimate exploitation rates and production.