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Michigan Technological University has undertaken a case study of the closing of the Sherwood mine. The objective of the study is to determine the nature and extent of changes which occur in the mine and its environs as a result of the mine closing. A monitoring program consisting of four major elements has been initiated. The elements are; hydrologic monitoring which consists of monitoring the water levels in seventeen surface wells, measuring levels flow rates at six stream gaging stations, and measuring the rise of water in two mine shafts; seismic monitoring which includes the monitoring of acoustic signals from geophones placed underground and in an array of surface wells; monitoring rock mass movement with underground sensors and; monitoring surface stability with subsidence monuments. The observations to date indicate a high probability of subsidence by a piping mechanism. The hydrologic monitoring has shown the development of a localized cone of depression above the workings. The cone is somewhat elliptical with an East-West axis. Flow calculations indicate an influx of water on the order of 2.4 x 106 gallons per day. This rate of water influx indicates that there are channels into the upper level stopes which may serve as conduits for the transport of overburden. The seismic sensors in the vicinity of the central and west pits have shown intermittent periods of high activity. This indication supports the idea that the precursor of subsidence; i.e. the transport of overburden, is occurring. Geophysical surveys of a small area south of the Sherwood Mine shaft do indicate the presence of some anomalies. The significance of these anomalies cannot be determined until further surveys are made. Extensometers on the 1000 ft. level of the mine have begun to show movement along an en-echelon fault parallel to the major shear which was investigated by the U. S. Bureau of Mines in 1966. The total movement to date has been O .092 inches. The extensometers are being continuously monitored and examined for signs of accelerating movement. The surface monuments which are surveyed on a regular basis have not shown any indications of movement. While we believe that the preliminary data indicates that piping is occurring, no conclusions represented at this time.
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· 1968
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