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Progressive Sinkhole Occurrence Induced by Dewatering Activities in a Large Lignite Mine SE Turkey

Ekmekçi, Mehmet
Yazıcıgil, Hasan
Following two successive massive landslides in 2011 with a total of 10 casualties at the Collolar open pit lignite mine located in southeast Turkey, an extensive dewatering program was initiated as a preventive measure against further slope stability problems. Based upon a series of studies on hydrogeological conceptualization and characterization, two major hydrostratigraphic units have been identified as target zones for dewatering. Failure in lowering groundwater in the Neogene sequence is has thus been attributed to the excessive inflow from karst aquifer. Therefore, a second dewatering program targeting the karst aquifer was scheduled and initiated in February 2015. Four sinkholes were developed progressively as a consequence of sudden collapse in a period of about 120 days after karst dewatering has started. Occurrence of sinkholes is restricted to an area of about 0.7 km(2) between the pit and the limestone outcrop. Progressive occurrence and development of sinkholes posed a serious risk for not only mining operations but also the settlements close to the sinkhole area. This study was conducted to explain the mechanism of sinkhole occurrence in the area and thereupon to suggest a solution to this hazardous risk. All information were put in a conceptual model that explains the most plausible mechanism of sinkhole occurrence which required a detailed comparative study of morphological, hydrographical, geological and hydrogeological characteristics of the sinkhole field and its near vicinity.