Britannica Sources used in this answer

Why does room-and-pillar mining become difficult at great underground depths?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

coal mining Schematic diagram of an underground coal mine, showing surface facilities, access shafts, and room-and-pillar and longwall mining methods.

At depths exceeding 400 to 500 metres, room-and-pillar mining becomes difficult to practice primarily due to excessive roof pressure and the requirement for significantly larger pillars to maintain stability.1

As mining operations descend deeper into the Earth, the weight of the overlying rock increases, leading to greater vertical pressure. Additionally, lateral pressure from the sides also intensifies with depth, depending on the local geology. In room-and-pillar mining, these forces must be managed by the coal pillars left behind to support the overhead strata. When the pressure becomes too great, the required size of these pillars increases to prevent failure, which complicates the extraction process and reduces the efficiency of the method. In extreme cases, such as in the world's deepest mines, this intense pressure can even result in rock bursts, where the rock fails violently.21