Susceptibility Assessment above Underground Mining Exploitations ? A Case Study in Bulqiza Mine

The sublevel open stoping mining method used in the chrome mine in Bulqiza has led to the creation of open spaces, which have been filled by the self-collapse of surrounding rocks located in the roof of the mineral body. For the Central and Southern area, the chrome ore deposit is at a relatively shallow depth of 0-100 m. The rocks of the roof have a variety of physical and mechanical properties (classified into bedrock and diluvional). The exploitable (recovered) thickness of the mineral body varies from 5 to 15 m. The horizontal and vertical extent of each ore body reaches up to 300 m and 100 m respectively and is affected by tectonics representing fluctuations from 15 to 30 m. On the ground surface of this undermined area are the presence of sinkholes and subsidence from mine roof failure. Studies have been conducted to determine the conditions leading to the development of the sinkholes and subsidence and to define the contours of the dangerous area, within which the possibility and intensity of risk vary. This paper presents an evaluation of the susceptibility using a method of mapping the influencing parameters (diluvional surface, bedrock surface, ore body surface, etc. ), weighting their impact based on the physical nature of the process and occurrences, superposition (Weighted Overlay) of these impacts and generation of a quality evaluation susceptibility map. Mapping of the influencing parameters and the evaluation of the susceptibility is performed using GIS technology.