Searching for possible precursors of mining-induced ground collapse using long-term geodetic monitoring data

Abstract

The problem of the ground collapses is common for the regions affected by the underground mining, as well as for the areas prone to the sinkholes of natural or human genesis. This paper describes the case of the ground surface collapse occurred in 2013 above the active Saranovsky chromite ore underground mine that has been operating for over eighty years. The results of pre- and post-failure high-precision levelling of the ground surface are presented. The monitoring network includes more than one hundred surveying points covering the area of about 1 km2 and since 2006 geodetic measurements have been conducted on an annual basis. The analysis pointed to a complex deformation process, manifested in the cyclic succession of subsidence and uplift of the surface. A local zone of continuous surface subsidence was identified immediately above the site of the future collapse. The deformations started several years before the failure. The extent of the subsiding area increased gradually, approximately approaching the size of the collapse (over 7000 m2). During the three-year period preceding the collapse, this area expanded by over a factor of ten, and the cumulated subsidence rate doubled. However, since the monitoring points located within the sinkhole area were lost, the data of the geodetic campaign carried out before the collapse were insufficient to estimate the value of the subsidence preceding the failure. Our results demonstrate, that in hard rocks mining-induced deformations can develop in utterly localized way. The progression of the subsidence was detected generally within the area of the future failure and did not extend significantly beyond its contours. In this paper, we highlight the importance of further development of the monitoring techniques and justification of hazardous deformation criteria for the early warning systems in mining regions and sinkhole-prone areas.