Seismic and geotechnical investigations following a rockburst in a complex French mining district

This paper presents the results of seismic and geotechnical studies carried out after a fatal accident that occurred during mining of the Frieda5 coal seam at Merlebach mine of HBL (Houillères du Bassin Lorrain, East France). On June 21, 2001, a violent rockburst (local magnitude of 3.6) affected the Frieda5 seam at depth of approximately 1250 m. The zone of the accident is located in the main gate 200 m ahead of the longwall face. Subsequently, an investigation was carried out to determine the causes of the accident and to understand the induced phenomenon. The program included an analysis of a comprehensive set of seismic data and the collection of in-situ stress measurements. The objectives were twofold: (1) to provide input data for the back analysis of the rockburst and (2) to identify other potential high-risk zones in the next panels to be mined. The joint analysis of the seismic, geological and geotechnical investigations suggests that the rockburst is largely due to a specific geological phenomenon, a sandstone channel in the floor of the coal seam characterized by high horizontal stresses.