Conference Agenda

Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).

Session Overview
14.2-1 Post-mining: Opportunities and challenges
Thursday, 23/Sept/2021:
1:30pm - 3:00pm

Session Chair: Dennis Quandt, Karlsruhe Institute of Technology
Session Chair: Tobias Rudolph, Technische Hochschule Georg Agricola (THGA)
Session Chair: Christoph Hilgers, Karlsruhe Institute of Technology

Session Abstract

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.

1:30pm - 1:45pm

Groundwater-systems in mining areas – The influence of water bearing adits

Tobias Rudolph, Christian Melchers, Peter Goerke-Mallet, Detlef Engel

Forschungszentrum Nachbergbau (FZN), Technische Hochschule Georg Agricola (THGA)

Water bearing adits form a historic near-surface underground drainage and outflow systems whose functionality is of considerable importance in many mining areas all over the world. Water bearing adits are technical structures that have often been in place and in operation for more than two centuries. In most cases, they are no longer accessible directly behind the tunnel portal. Therefore, stable hydraulic, geotechnical and rock mechanical conditions are important, otherwise the hydraulic system would collapse.

In recent years, the Research Centre of Post-Mining has investigated the current situation of a large number of water bearing adits in the southern Ruhr area/Germany. To understand the interaction with the groundwater- systems hydrochemical parameters were analysed, the rate of discharge and of precipitation compared. An essential step is the spatiotemporal evaluation of available mine survey maps of the water bearing adits and the hydraulically connected mine workings. This is needed in order to determine the catchment area of a water bearing adits within the groundwater-system.

To further enhance the process understanding the results from monitoring-stations, special depth-dependent hydrochemical sampling campaigns in former shafts and infiltration/tracer tests in ditches/local streams were integrated. The entire data fusion happened in 3D geological/hydrogeological subsurface models. This integrated subsurface understanding is now the enabler for the implementation of a risk monitoring and management system for this sensitive system of water bearing adits.

1:45pm - 2:00pm

Mine water rebound in German hard coal mines – geochemical and petrophysical data support for an integrative monitoring plan

Henning Jasnowski-Peters, Barbara M.A. Teichert, Till Genth, Lisa Rose, Christian Melchers

Research Center of Post Mining, Technische Hochschule Georg Agricola University, Germany

Mine water rebound in German hard coal mine areas operated by RAG AG under the leadership of RAG Foundation is a showcase for post-mining associated research. It is a long-term, cost intensive and multidisciplinary project affecting highly populated urban areas like the Ruhr District. RAG is facing long-term liabilities as regulatory framework for the rebound process. Currently, mine water is pumped from levels down to 1200 meters to be discharged into local rivers. In the vicinity, monitoring water wells were drilled to identify any hydraulic potential changes in the overburden sections in support of the project’s risk assessment. Mine water management issues comprise control and forecast of mine water levels including to determine a financially and environmentally sustainable level. Mine water treatment, evaluating hydraulic barriers, but most importantly, protecting groundwater for domestic use and even more critical, regional drinking water reservoirs are mandatory prerequisites. We identified natural hydrochemical tracers, worked on in-situ processes affecting mine water chemistry and progressed with petrophysical measurements on core material including clay mineralogy screening to deliver a first step towards an integrative monitoring approach to manage such liabilities. A suite of own and literature-based hydrogeochemical and petrophysical data are presented to better describe the regional hydrology and geology.

2:00pm - 2:15pm

FloodRisk: Earthquakes, uplift, and long-term liabilities – risk minimisation during mine flooding

Dennis Quandt1, Michael Alber2, Felix Allgaier1, Benjamin Busch1, Even Markus3, Kasper Fischer4, Wolfgang Friederich4, Jonas Greve5, Mathias Knaak5, Birgit Müller6, Thomas Niederhuber6, Detlev Rettenmaier7, Martina Rische4, Thomas Röckel8, Frank Schilling6, Daniel Schröder9, Olaf Ukelis7, Malte Westerhaus3, Roman Zorn7, Christoph Hilgers1

1Institut für Angewandte Geowissenschaften, Strukturgeologie & Tektonik, Karlsruher Institut für Technologie; 2Alber Geomechanik, Dortmund; 3Geodätisches Institut Karlsruhe, Karlsruher Institut für Technologie; 4Institut für Geologie, Mineralogie & Geophysik, Ruhr-Universität Bochum; 5Geologischer Dienst NRW, Krefeld; 6Institut für Angewandte Geowissenschaften, Technische Petrophysik, Karlsruher Institut für Technologie; 7European Institute for Energy Research, Karlsruhe; 8Piewak & Partner GmbH, Bayreuth; 9Civil & Mining Engineering, DMT GmbH & Co. KG, Essen

Due to the cessation of coal mining in Germany, mine water management in the former coal districts is subject to change and of environmental and economic significance. Since there is no technical need to drain the abandoned coal mines, mine water levels rise. As a result, subsurface rock pore pressures rise changing the subsurface effective stress regime. This may induce local ground movements and activate mining-related and natural fault zones.

In order to develop a better understanding of the processes and their interaction, FloodRisk applies an interdisciplinary approach involving geological, geomechanical, geodetic, and geophysical methods. For this purpose, former German coal districts in the Saarland, Ruhr area, and Ibbenbüren serve as suitable study areas.

Based on a geological 3D subsurface model complemented by petrophysical (porosity and permeability) and structural data (fracture network characterization), geomechanical properties such as slip and dilation tendencies of faults were calculated. These data give insights into the expected fault behaviour under assumed stress conditions and provide a basis for the localisation of suitable areas for soil gas measurements (222Rn, 220Rn, CO2, O2, H2, S, CH4) using recently developed economic sensors. Simultaneously, seismic events and ground movements are continuously monitored using seismic network, GNSS, Nivellement, and InSAR data and subsequently compared with the evolution of mine water levels. These multidisciplinary observations will be combined in a conceptual model on flood-induced ground movements and seismicity. This enables the deduction of operations for future mine flooding and the establishment of an optimised reservoir management.

2:15pm - 2:30pm

Analysis of surface displacements caused by mine flooding for the project FloodRisk with SAR Interferometry, GNSS and Levelling

Markus Even1, Malte Westerhaus1, Daniel Schröder2

1Karlsruhe Institute of Technology, Germany; 2Civil and Mining Engineering, DMT GmbH & Co. KG, Essen

After operation of hard coal mines has been terminated in Germany, many of the mines are being flooded. In the project “FloodRisk: Earthquakes, uplift, and long-term liabilities – risk minimization during mine flooding”, the consequences of the rising mine water levels are investigated from a multidisciplinary perspective. Geodetic, geophysical, geomechanical and geological approaches are combined to develop a conceptional model for flooding induced surface displacements and seismicity. Saarland, Ruhr area and Ibbenbüren have been chosen as exemplary investigation areas.

The DMT GmbH & Co. KG (DMT) and the Geodetic Institute Karlsruhe (GIK) contribute to the project by analyzing surveying and InSAR data. DMT installs ten low-cost GNSS-Sensors near Bergwerk Ost and includes them in DMT SAFEGUARD, a proprietary GNSS monitoring system, that provides an integrated evaluation and provision service. GIK is analyzing InSAR data from Sentinel 1a/b and intends to combine GNSS, levelling and InSAR data from different orbits to derive 3D displacements. Challenges that are typical for mining areas as the spatially as well as temporally diverse displacement patterns demand for new solutions in InSAR processing. The so found displacements of the earth’s surface will be integrated with geomechanical modeling in the final phase of the project. In this presentation, the goals, challenges and approaches of FloodRisk with regard to geodesy are discussed and first results are shown.

2:30pm - 2:45pm

FloodRisk: Observations of rising mine water level and micro seismicity in the eastern Ruhr area (Germany)

Martina Rische, Kasper David Fischer, Wolfgang Friederich

Institut für Geologie, Mineralogie & Geophysik, Ruhr-Universität Bochum

FloodRisk is an interdisciplinary project focusing on the effects of mine water level rise in abandoned coal mine regions in Germany. Such effects are heterogeneous ground uplift, stress changes due to the change in pore pressure and the reactivation of potential faults. One of the most directly measurable effects is the induced micro seismicity.
In this study the relationship between mine water rise, fluid-induced stress changes and induced seismicity in the Haus Aden dewatering area in the eastern Ruhr area (Germany) will be investigated in more detail. For this purpose, we operate a network of short period seismic stations in the region of the former "Bergwerk Ost" colliery, which had the highest seismicity rate in the Ruhr area during active underground coal mining (closed 2010).
Level of induced seismicity started again when pumps were shut down (mid 2019). We were able to detect and localise more than 1000 microseismic events in magnitude range between -0.7 and 2.6 Mlv. Many of these events are spatially clustered and some show quite high waveform similarity. This allows relative localisation and can increase the accuracy of the location. The depth location of the earthquakes, within the limits of localisation accuracy, agrees very well with the distribution of seismicity at the time of active mining. The measured temporal trend of the mine water level shows a strong correlation with the temporal evolution of the observed micro seismicity.

2:45pm - 3:00pm

PostMinQuake: Potential Learnings of induced seismicity during post-mining in European coal regions

Maria Paloma Primo Doncel, Peter Goerke-Mallet, Stefan Möllerherm, Tobias Rudolph

Forschungszentrum Nachbergbau - Technische Hochschule Georg Agricola, Germany

The task of this European research project (PostMinQuake) is to identify mechanisms, relevant parameters and dependencies causing post-mining seismicity for several European coal regions.

When closing an underground coalmine, the mine water raises by stopping mine water pumping, which can lead to micro seismic events due to the final change of the geomechanical stress-regime.

The consortium partners (FZN-THGA, GFZ, BRGM, INERIS, CMI, SUT, SRK, IGN, Green Gas, DIAMO) will collect and analyse information from the coal basins Gardanne (France) and Upper Silesia (Czech Republic and Poland). In Germany, we will focus in the Ruhr Basin and Ibbenbüren (North-West Germany), which are places with centuries of hard coal mining history and where mining ceased in 2018.

In order to detect the processes that cause micro-seismicity, we are gathering information in the basins regarding geology; mining methods and monitoring protocols; and post-mining situation and seismicity.

This information will be analysed to identify similar approaches to develop a synthesis of good practices, compulsory and desired improvements, as well as an post-mining seismicity map for post-mining seismicity diagnosis. We also aim to develop a Ground Motion Prediction Equation, and the elaboration of criteria of hazard rating.

The final guideline could help the mining industry and decision-making bodies to manage the risks of post-mining micro seismicity, also of interest in old petroleum reservoirs when used to storage H2 or even for geothermal energy.

Acknowledgements: The Research Fund for Coal and Steel funds the PostMinQuake project under the grant agreement No 899192.