Socio-economic, subsidence, transportation, and legal ramifications of potential liquefaction plant sitings. Task B. Prediction of subsidence potential over abandoned mine land. Quarterly report, October 1-December 31, 1983

Subsidence over active longwall mines, which occurs concurrently with mining or is completed within a few days following coal extraction has been studied extensively over the past decade. On the other hand, subsidence over abandoned coal mines is difficult to predict and may take place decades after mining has ceased. Two types of delayed subsidence are normally observed: troughs, which are shallow depressions, and sinks, which are steep-sided pits. Both types of delayed subsidence may cause damages to surface structures. Most of the abandoned coal mines in the Appalachian coal field were mined by the room-and-pillar method. These mines generally are very shallow and are very irregular with unsupported roof spans of varying widths. The approach adopted in this research for predicting the subsidence potential over abandoned coal mines focuses on the development of a mathematical model, essentially a finite element model capable of modeling the viscoelastic behavior of rocks and coal. The simulation of the viscoelastic behavior of rocks and coal is needed for predicting the delayed subsidence. The assessment of subsidence potential over abandoned mine land is currently being conducted on two sites. Site investigation is aimed at obtaining the following data: surface topography, information on the overburden,more » local geology and ground crater hydrology, the physical and mechanical properties of the rock strats, past subsidence damages, if any, in the area, and the old mine maps. Most of the physical and mechanical properties of the rock strata will be obtained, if possible, from previous tests performed on similar types of rocks. Information on the viscoelastic behavior of the rocks and coals, however, are very scarce.« less