Bock, Barbara (Ruhr-University Bochum) | Alber, Michael (Ruhr-University Bochum) | Rogall, Michael (Geological Survey and Mining Authority of Rhineland-Palatinate) | Wehinger, Ansgar (Geological Survey and Mining Authority of Rhineland-Palatinate) | Scherschel, Jürgen (Baugrundinstitut Franke-Meißner und Partner GmbH) | Sachtleben, Volker (Baugrundinstitut Franke-Meißner und Partner GmbH)
As a relict of former subsurface basalt mining activity within the municipal area of the city of Mendig (Germany) an area of about 200,000 m² of disused pillar supported mining openings still exists at about 15-20 m below the current ground surface. After the shutdown of mining, numerous pillars experienced brittle deformation and several surface collapses occurred. To prevent any further harmful damages, a risk assessment with modeling of relevant parts of the mining openings is carried out currently. The geomechanical input data for modeling are based on the results of numerous laboratory tests. The test results indicate that pillar failure is strongly influenced by a combination of particular pillar properties like geomechanical properties as well as geometric pillar properties.
In the course of the 19th and 20th century extensive subsurface mining activities for the exploitation of the well-known "Mendig basalt" have left behind exhausted stope-and-pillar mining plants below the city of Mendig, Germany. During the mining activities, the remaining pillars had to ensure the support of the overburden and to provide a stable and safe surface environment.
For some of the basalt pillars below the meanwhile intensely developed urban areas of Mendig, the uniaxial compression strength (UCS) has been exceeded later on and consequently the corresponding pillars experienced brittle deformation after the shutdown of the mining plants.
In order to assess the currently given rock mass strength of the remaining pillars, the mechanical properties of the pillars (e.g. uniaxial rock and rock mass strength) as well as the geometrical properties of the pillars (e.g. cross sectional area, height, shape, axial orientation and slenderness) have to be considered.
The compilation and interpretation of a corresponding data base is the topic of a current research project. The project includes desk studies and site investigation drillings for the exploration of further suspected subsurface mining areas, 3D laser scanning and geotechnical mapping of known and explored mining areas, as well as core sampling, the execution of laboratory tests, and the numerical modeling for the stability assessment of known mining areas.