Mine Subsidence Information

• Mine subsidence is movement of the ground surface as a result of the collapse or failure of underground mine workings. In active underground mining operations using longwall mining or high extraction pillar recovery methods, subsidence can occur concurrently with the mining operation in a more predictable manner.
• In abandoned mines where rooms and unmined pillars are often left in various sizes and patterns, it may be difficult to predict if and when subsidence will occur. Mine subsidence resulting from abandoned room and pillar mines can generally be classified as either sinkhole subsidence or trough subsidence.
• Sinkhole subsidence occurs in areas overlying underground mines which are relatively close to the ground surface. This type of subsidence is fairly local and is recognized by an abrupt depression evident at the ground surface as overburden materials collapse into the mine void. Sinkhole subsidence is perhaps the most common type of subsidence. It is responsible for extensive damage to many structures and gross environmental damage.
• Subsidence troughs over abandoned mines usually occur when the overburden sags downward due to the failure of remnant mine pillars, or by punching of the pillars into a soft mine roof or floor. The resultant surface effect is a large, shallow, yet broad, depression.
• Subsidence is usually greatest at the center of the trough and it progressively decreases until the limit of the surface area is reached. Horizontal ground movements also occur within a subsidence trough. Structures near the center of the trough can experience damage caused by the compression of the ground surface, and structures near the edges can be damaged by tension or stretching of the surface.
• Ground movement within a subsidence trough can result in damage to buildings, roadways, bridges, railroads, underground pipelines and utilities, and practically any other structure or feature that may be present. The flow of streams may be altered or disrupted, and surface cracks may occur, particularly near the edges of the trough.

Details of Coal Mine Subsidence