Foundation Response to Subsidence Induced by High Extraction Mining in Southern Illinois

The Bureau of Mines, in cooperation with the Illinois Mine Subsidence Insurance Fund, is monitoring the response of two foundations to ground movements induced by subsidence from a high-extraction retreat room-and-pillar operation in southern Illinois. The objective of this monitoring program is to study the inter- action between the ground surface and a structure during a subsidence event. Data from such a study should enhance the understanding of the mechanisms that produce structural damage and aid in the design of structures that resist such damage. This paper describes the monitoring instrumentation and techniques as they relate to the mining and site conditions. The capability of a tiltmeter to detect and follow the tilt of the foundations caused by the mining subsidence sequence is demonstrated. Using data from this tiltmeter, the development of curvature in the foundations as they conformed to the displaced ground surface is shown. This curvature is rep- resented by differences in tilt at various points on the foundations, indicating a change in tilt over a horizontal distance. Also, even though subsidence damage has not been fully analyzed, preliminary observations of the cracks that formed in the foundations are reported. These cracks resulted in the separation of one footing into distinct pieces; therefore, their effect on the tilt readings is cited.