After the closure of mines in Germany, former districts are nowadays subject to changes, which may require geomonitoring. This concerns the mine water management in particular as pumping of mine water in the abandoned mines is technically not necessary anymore. As a result of the controlled mine water rebound, fluid pore pressures in subsurface rocks increase and may alter the stress state of the subsurface rocks. The increased pore pressures may result in geomechanical changes in the deeper subsurface around the mine. This may result in ground movements and micro-seismic events, which may be measured on the surface. Post-mining also provides an opportunity for post-usage, such as new natural (geo)heritage sites or geothermal energy. Thus, centuries-long active mining produced a wealth of geological, geodetic, geophysical, and geomechanical data. Based on such multidisciplinary data, interdisciplinary geological models and technical solutions can be developed and applied to different mining areas worldwide where active mining has been closed. This session invites contributions from different scientific disciplines that study the processes that undergo in post-mining areas in Germany and globally. Among others, this may include geology investigating sediment or rock properties and structures on different scales, geophysics detecting fluid-induced micro-seismic events and studying stress fields, and geomonitoring of ground movements or gas emissions. It may address strategies to improve land rehabilitation above and below ground.
4:15pm - 4:30pm
Soil gas monitoring for identifying potential ground movements and earthquakes in the frame of mine flooding - Requirements, methods and developments
European Institute for Energy Research, Germany
Soil gas surveys (e.g. 222Rn, CO2, O2 etc.) are very well known in diverse backgrounds such as the detection of geological faults, prediction of earthquakes or monitoring of gas contamination risks at building sites. Risk monitoring using soil gases in the frame of mine flooding is a quite new field of application currently investigated in the frame of the German BMBF funded project FloodRisk. Analogies to some of the classical soil gas applications highlight a relevant potential for technology transfer to the mining industry. Flooding of closed-down mines can induce ground movements and earthquakes that can potentially be monitored with soil gases provided that site-specific characteristics meet soil gas survey requirements. Such relevant requirements, as well as standard soil gas methods used, but in particular also first steps for new, low-cost sensor developments for permanent soil gas monitoring will be presented in this contribution.
4:30pm - 4:45pm
Fracture network characterization and DFN modelling of the Upper Carboniferous, Ruhr Area, Germany
1Structural Geology & Tectonics, Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT); 2Technical Petrophysics, Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT)
Since coal mining in the Ruhr Area has been ceased, mine water drainage is gradually reduced leading to the rise of formation water and groundwater levels. Rising mine water levels increase the pore pressure and induce stress changes in the subsurface, which may reactivate natural and/or mining-related faults and fractures. As part of the interdisciplinary FloodRisk project, which aims to enhance the understanding of the geomechanical coupling of increased pore pressure and heterogeneous ground movements, we present a geological km-scale 3D model of a former mining area hosted in the Upper Carboniferous. Fault and horizon geometries are constructed based on coal seam mappings from the Geological Survey of NRW.
Beside the integration of petrophysical data, a discrete fracture network model (DFN) is implemented to capture the fracture network of the subsurface. Therefore, Upper Carboniferous outcrops were studied by UAV-derived 3D outcrop models to analyse fracture parameters. Fracture network characterization revealed five dominant fracture sets with striking orientations of N-S, NE-SW, ENE-WSW, WNW-ESE and NW-SE. Calculated dilation tendencies provide information on which fracture sets are likely to contribute to fluid flow in the subsurface. A DFN model is stochastically modelled based on these “effective” fracture sets and will be the basis for the construction of a simulation model.
4:45pm - 5:00pm
Sensor fusion – An new approach towards a digital twin in geoscience and post-mining
1Technische Hochschule Georg Agricola, Germany; 2Geologischer Dienst Nordrhein-Westfalen, Germany
Geomonitoring of mining processes is a very current topic. Geomonitoring uses modern surface and subsurface methods observing the Earth’s surface. “Digital Twin” is a research project whose main goal is to use methods to detect surface and subsurface trends in post-mining areas and relate them to environment processes (e.g. climate changes). An important aspect it to distinguish between environment and artificial/mining influences and effects. The research area of this project is the closed Prosper-Haniel coal mine. The project uses modern research methods and instruments ranging from modelling the geological subsurface in order to visualize the model in three-dimensional space. Through a spatiotemporal analysis of available satellite data and verify the results, in-situ mapping using a mobile GIS application or copter flights with multispectral and thermal sensors are deployed. Each of the sensors play an important role in project “Digital Twin”, but collaboration and combination of different domains allows a broader view of the problems of environmental and geoscientific processes.
5:00pm - 5:15pm
TRIM4Post-Mining: an integrated planning tool for the transition from coal extraction to re-vitalized post-mining landscape
1Forschungszentrum Nachbergbau, Technische Hochschule Georg Agricola, Bochum; 2Technische Universität Bergakademie Freiberg, Freiberg
The TRIM4Post-Mining project aims to develop an integrated information modeling system to support decision-making and planning during the transition from coal exploitation to a re-vitalized post-mining landscape, enabling infrastructure development for agricultural and industrial uses and contributing to the recovery of energy and materials from coal mining dumps. This modeling system will be composed of a high-resolution spatiotemporal database founded on state-of-the-art multi-scale and multi-sensor monitoring technologies to characterize dynamical processes in coal waste dumps related to timely dependent deformation and geochemical processes. To test this approach, the European consortium formed by experts from industry and academia (FZN-THGA, TUBAF, TU DELFT, MIBRAG, Beak Consultants, Spectral Industries, and Eijkelkamp SonicsSampdrill) will compile and analyze data from the Schleenhain Mine dump in Leipzig, Germany. In this context, comprehensive spatiotemporal data analytics, feature extraction, and predictive modeling will be developed to target potential contamination areas and forecast the waste dump dynamics. All the up-to-date data and models will be embedded in an interactive planning system based on Virtual Reality and Augmented Reality technology forming a TRIM – Transition Information Modelling System that guarantees efficient and transparent communication of planning scenarios in terms of residual risks, technical feasibility, environmental and social impact between all key stakeholders.
5:15pm - 5:30pm
Burggraf-Bernsdorf – transformation of a potassium mine to a UGS facility
Untergrundspeicher- und Geotechnologie-Systeme GmbH, Germany
The potassium mine Burggraf-Bernsdorf was established between 1911 and 1913. It was situated at the southwestern flank of the Roßleben saddle (Sachsen-Anhalt) and belonged to the “Unstrut Kalirevier”. About 300.000 tons of carnallitite were extracted. The mined cavity was about 175.000 m³. Due to a reorganization of the German potassium industry the mine was closed in 1921.
After a 40 year long period of quietness the abandoned mine was investigated for its suitability as an underground gas storage facility (UGS). The project was regarded as a large-scale test firstly. Safety criteria were developed and investigations were conducted in the fields of rock mechanics, explosion hazards and of physicochemical interactions. The storage phase started in 1970 after installation of an effective seal into both shafts. Due to the small capacity the UGS was used as a buffer store of the regional gas grid. About 1,4 billion m³ of gas were handled during the operating phase.
In 2014 the operator decided to close the UGS due to the high wetness of the produced gas and the complexity of a refitting of the facility. Several methods were checked to abandon the UGS. Dry abandonment was compared with flooding with different media. Aspects of rock mechanics, of leaching kinetics and of environmental studies were considered during this procedure. The abandonment of the mine, the removal of the casing and the backfilling of the shafts happened between 2018 and 2020. A five year long monitoring period will finalize the history of the multifunctional mine Burggraf-Bernsdorf.
5:30pm - 5:45pm
Geomonitoring as a contribution to process understanding of river renaturation in post-mining areas – Example: Emscher catchment
Technische Hochschule Georg Agricola, Germany
The Emscher, formerly discredited as the "Köttelbecke", is being renaturalised at great expense by the EMSCHERGENOSSENSCHAFT / LIPPEVERBAND in the course of post-mining activities. In addition to the Emscher Canal as the central structure, this primarily affects the Emscher itself and the receiving waters in the catchment area, such as the Boye. River areas that have been redesigned to be close to nature are to be gradually transformed into functioning natural areas.
Today the project faces the challenges of climate change. The question arises whether the Emscher can be supplied with enough water from the catchment area in the future to achieve the ambitious goals? FZN is tackling this question on behalf of EGLV together with its partner EFTAS. A complex data mix of sentinel satellite data, special multicopter sensor technology, in situ sensors and soil samples are fused in a model test to calibrate each other. This will result in a better hydro(geo)logical process understanding of the catchment over a hydrological year. The aim is to obtain area-wide, but reliable statements via the satellite level to be able to transfer the model test to other catchments.
The lecture presents first results from the copter and in situ level. It describes the procedure and approaches for the experimental setup and the evaluations. In this context, inexpensive RFID/NFC data loggers from the greenhouse sector are tested for the first time to see how they can contribute to the overall hydrogeological/geological understanding as a future in situ component.