Case study of sinkholes over a Nebraska limestone mine.
Siekmeier-JA; Triplett-TL; Powell-LR
Abstract Book, U.S. Department of the Interior Conference on the Environment and Safety, April 24-28, 1995. Washington, DC: U.S. Bureau of Mines, 1995 Apr; :46
The USBM responded to a citizen's request for assistance when five sinkholes, each 20 m to 25 m in diameter, developed within a 90 m by 105 m area on agricultural land overlying an abandoned section of an underground limestone mine. It was determined that the subsiding area could enlarge due to three mechanisms: (1) caving and sliding of soil into the existing sinkholes, (2) new roof falls in the mine adjacent to the existing sinkholes, or (3) new pillar failures in the mine adjacent to the existing sinkholes. The safety of agricultural workers was the main consideration at the site and so it was recommended that a buffer zone be created around the subsiding area based on the mechanism that could cause the greatest sudden increase in the subsiding area. Drilling logs were used to create a geologic model from which a simplified computer simulation of the stress distribution in the rock mass was developed. It was determined that the vertical stress had increased in the pillars near the existing sinkholes during sinkhole formation and that this may have weakened the nearby pillars. These pillars are currently stable, but may eventually deform or fail due to this weakening. Subsequent roof failure would then result in enlargement of the existing sinkholes. Therefore a buffer zone extending 43 m from the edge of the existing sinkholes was recommended.
Case-studies; Mining-industry; Soil-sampling; Soil-analysis; Environmental-factors; Mine-shafts; Safety-monitoring; Safety-research; Agricultural-industry; Models; Rock-mechanics
Conference/Symposia Proceedings; Abstract
U.S. Bureau of Mines