How can underground coal mining cause surface subsidence?

Surface subsidence occurs in underground coal mining when the extraction of coal leads to the collapse of the overlying rock strata. As coal is removed, the support for the layers of rock above the mine is weakened or eliminated, causing these layers to cave in.12

This process can manifest in two primary ways:

• Complete Collapse: In methods such as longwall mining, the roof behind the active mining face is intentionally allowed to cave in as the supports advance. This caving of the overlying strata can propagate upward through the geologic medium until it reaches the surface, resulting in surface depressions.123
• Structural Instability: In other mining systems, such as room-and-pillar, the stability of the surface depends on the design of mine entries and pillars. If the extraction of coal is too extensive or if pillar stability is compromised, the resulting structural failure can also travel to the surface, causing subsidence.1

To mitigate these effects, engineers may use rock mechanics to design mine layouts or employ backfilling techniques to fill voids with materials like sand or waste.12