Types, Causes, and Effects of Instability Phenomena in Reclaimed Spoils At Two Surface Coal Mines in Western North Dakota.
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Monitoring of reclaimed surface mine spoils at the Indian Head and Center Mines showed 3 forms of instability; area wide settlement, localized collapse, and piping. Over 200 survey markers were installed at the two mines and monitored from 1977 thru 1982. Area wide settlement at the Indian Head Mine avg 3 cm over 3 yr. Some movement was missed because survey monuments were installed a yr after spoils placement. Settlement at the center mine avg 12 cm over 3 yr; most settlement occurred in the first 15 months. These data indicate that settlement time should be provided before structures are built on spoils or settlement monitored during construciton. Localized collapse was observed at both mines. The contractor determined the cause to be the thawing and subsequent compaction of frozen spoils contoured with a bulldozer. All collapse features ended within 15 months of the contouring completion. The largest feature seen was 15 m long and 3 m deep. Piping was observed at the Indian Head study site. Piping features reached a max. Dia. of 3 m and were typically 0.5 to 1 m in dia. They typically first appeared after a rainstorm as small openings through the topsoil and underlying spoils. Drainage into the pipes enlarged the opening. Piping appears to be controlled by a combination of physical and chemical cond. In the soil. Near- surface sodic spoils that shrink and swell more than non-sodic soils may increase infiltration and subsequent piping formation. Development of piping can be a severe long-term stability problem. This vol summarizes the results of the study.
CP; Final Contract Report;
For Reference Only At Bureau Libraries
N.d. Geological Survey