ABSTRACT
The analysis of mining-induced changes in the overburden provides a better understanding of the mechanisms which lead to the surface expression of subsidence and hydrologic changes. The study site is located in the flat to gently rolling farmland of south-central Illinois. The overburden consists primarily of Pennsylvanian shales and siltstones overlain by 20-25 feet of glacial drift. Pre- and post-subsidence field investigations included geotechnical and geophysical logging of inclined core holes and the monitoring of survey monuments, piezometers and time domain reflectometry cables. In the laboratory, core samples were tested for unconfined compressive strength and modulus of elasticity. Post-subsidence drilling was difficult due to fracturing in the overburden. Time Domain Reflectometry cables were used to document strain and fracture development in the overburden. Piezometric levels in the overburden decreased as fractures developed due to the tensile portion of the traveling subsidence wave.
