This report covers the cumulative studies on mine subsidence in Michigan underground iron mines, with particular emphasis on the investigations by The Cleveland-Cliffs Iron Company. Most of the information and effort have been related to the Marquette Iron Range, the oldest in the Lake Superior region.
A historical summary is presented with a brief description of the geology of the Marquette Iron Range. Sketches of some early subsidence case histories are related.
This report describes in detail the methods employed in recent years, (1945-1960), in collaboration with the U.S. Bureau of Mines. Cleveland- Cliffs' program was directed towards detecting the possible subsidence from underground workings by the use of instrumented diamond drill holes. For the most part, these holes were specifically drilled for this purpose. Application of the microseismic method of predicting rock failure is discussed in a variety of circumstances. Also described is the use of surface subsidence pin surveys, interval velocity studies, and reflection seismic surveys. Detailed tests on complete physical properties of selected earth materials are discussed with reference to geologic structures.
The company has considered a variety of techniques in its effort to predict the progress of subsidence. These studies have shown the complexity of the various factors and indicated the difficulties in predicting the place and time of mine subsidence. The cost of the use of these techniques is a major factor to consider in future applications.
In order to apply any of the techniques described in the report, it is necessary to obtain considerable basic data relating to the physical properties of the various rock types and the general geologic structures. The greatest single factor in mine subsidence is the relationship of the geologic features to the mining methods in underground mining.
