TH Georg Agricola

The ground below Gronau and the surrounding area is a challenge, even for geologists: Salt has been mined here intensively for almost 50 years. This has created large cavities, known as caverns, at depths of between 1,000 and 1,500 m. Most of them are now used to store natural gas, crude oil or helium, and are important to the economy of the entire region. Right next to this cavern field is Amtsvenn nature reserve, spanning 9 km² of moorlands.

This special place has been the frequent source of tension over the years – not only in the geological structures themselves, but also between residents, the city and the various operating companies. The main cause of this tension is the ground motion, which in the long term could lead to subsidence in the area and consequently cause damage to buildings and alter the water balance. But what is actually caused by mining? And what is caused by nature? This is where a new, unique research cooperation, formed to investigate Epe cavern field, comes in. The new cooperation includes the City of Gronau, the citizens’ group Bürgerinitiative Kavernenfeld Epe e.V. (BIK), EFTAS Fernerkundung Technologietransfer GmbH and the Research Center of Post-Mining (FZN) at TH Georg Agricola University (THGA) in Bochum (Figure 1). Together, they want to find a solution to determine where the ground motion in the cavern field is coming from. “In order to understand the processes in detail, it is crucial to carry out tailored, extensive monitoring of all factors that are having an impact on ground motion in the region,” explains Prof. Peter Goerke-Mallet from the FZN. This includes satellite data from Copernicus, the EU’s space programme, as well as the use of local infor-mation and the knowledge of residents.

“Above all, we want to use this new research cooperation to establish a foundation of trust,” says Prof. Goerke-Mallet. “Today, all mining projects require transparency and the extensive sharing of expertise with society and vice versa. In this project, we can benefit from the knowledge of local people in a really special way,” says the experienced mine surveyor and mining expert. “After all, the residents know best where the challenges lie in their local area and can observe and document the changes in the landscape and buildings, sometimes even over years and decades. The research cooperation for Epe cavern field therefore offers a highly innovative approach to conflict resolution through active participation.”

Holger Perrevort, chair of the citizens’ group, also hopes that the cooperation will improve the flow of information and create more opportunities for involvement. “Above all, we want more accurate information about what is happening right below our very feet.” A lot has gone wrong here in the past, according to the resident. Not enough attention was paid to the potential risks and impact of ground motion, Perrevort says. “As a citizens’ group, we have been fighting for our concerns to be taken seriously for years already. Politicians must also fulfil their duty of care towards residents, e. g., if cellars get wet or cracks appear in walls.”

The experts at the FZN in Bochum also want to get to the bottom of this damage. Over the next twelve months, they will perform specific measurements to investigate the issue – using drones, which can detect changes in vegetation, e. g., and satellite data, which the specialists from EFTAS in Münster will analyse. “But we will also make a deliberate effort to visit the locals, to conduct building inspections and measure buildings and properties that may have been affected by ground motion,” explains Prof. Tobias Rudolph, a geomonitoring expert at the FZN. “Close cooperation with local residents is vital for us to be able to complete this work, so we are extremely grateful that new doors have been opened to us in this respect – in the truest sense of the word.”

The scientists are likely to spend most of their time analysing the large volume of data: “We will examine information on the groundwater and the surrounding bodies of water, on the ground, the subsurface and the caverns, among other things.” Their contact with members of the citizens’ group and the city also gives them access to many other important sources of information, such as private measuring points, springs and municipal geodata, which they plan to link together and analyse. Naturally, this will not all be done behind closed doors, but rather – in keeping with the pursued aim of transparency – alongside regular information events, where the results will be freely disclosed and discussed.

This planned approach also convinced Rainer Doetkotte, the Mayor of Gronau, to add his signature. Most importantly, he can envisage the positive effects this cooperation will have on the region in the long term: “This research cooperation marks the start of an important project, and I am delighted that we have the FZN, EFTAS and BIK on board for it. Ultimately, we want to provide the interested public with detailed information using the results obtained, in order to resolve any concerns, dispel any prejudices and increase acceptance within society. The results can also be used to create other concepts in the future, bringing further scientific progress to Gronau.” (THGA/Si.)

Intensive mining has caused the terrain and surface to sink so substantially in some areas in the Ruhr area that large depressions have formed – referred to as polder areas. In these areas, waterways cannot always flow freely anymore. The “lower” areas therefore need to be continuously artificially drained to prevent the accumulation of water from rivers and lakes. These processes have a big impact on the overall water balance in the region. In a new project, the Research Center of Post-Mining (FZN) at TH Georg Agricola University (THGA), Bochum/Germany, is therefore investigating how water management in the Ruhr area can be made more sustainable. Any resulting measures could particularly benefit the farmers and the forests in the region. The planned environmental monitoring should also improve the management of extreme events, such as heavy rainfall or long periods of drought. This is where the “MuSE” project (Multi-sensor geomonitoring for sustainable polder management) comes in.

MuSE is being funded by RAG-Stiftung until 2024. Bärbel Bergerhoff-Wodopia, Member of the Board of Management at RAG-Stiftung, stresses: “At RAG-Stiftung, we believe we have a responsibility to find solutions to the challenges that mining has left behind. With this in mind, we are working closely with THGA and the Research Center of Post-Mining and are supporting the “MuSE” project with firm conviction.”

“In areas where the land has sunk as a result of coal mining, that is where large depressions have formed in the ground, the soil moisture has also changed,” explains Prof. Tobias Rudolph from the FZN. In some cases, entirely new bodies of water have been created, like Weihnachtssee lake or Ewaldsee lake in Herten (Figure 1). “This naturally has an impact on the use of land and resources for agriculture, forestry and water management. This has far-reaching consequences – particularly because of climate change,” says the geomonitoring expert. The lower levels of precipitation and increased periods of drought over recent years have made this clear: “The Ruhr area needs more water in order to cope with the effects of climate change in the long term – even if the events of the last few weeks may cause you to think otherwise.”

Prof. Rudolph and his team are therefore investigating alternative solutions for the management of polder water drainage, namely: “What can we do to make better use of this water? And how can we optimise irrigation planning in general?” In the new MuSE research project, the experts at the FZN are investigating how to redesign polder management so that it is efficient and sustainable. Higher groundwater levels and the economic and technical use of elevated groundwater and surface water, e. g.,  could help to minimise drought damage in agriculture and forestry. Targeted monitoring can also help ensure that polder areas are better set up to cope with heavy rainfall and flooding.

To this end, not only are the experts at the FZN analysing the historic data available, they are also using modern satellite data and performing their own measurements in selected test areas: “We use various sensors to measure the soil moisture. We also analyse water level data and survey the vegetation using our drones, examining the health of the plants at the same time. We combine this information that we have gathered locally with remote sensing data supplied by the European satellite programme Copernicus and evaluated for the first time with regard to this issue,” explains Xiaoxuan Yin, a specialist in radar interferometry and remote sensing who joined the FZN in order to work on the project.

Then it gets a bit trickier: “We combine all the different pieces of information in a 4D model using time as the fourth dimension,” explains Yin. This enables the scientists to track the changes in the water balance over the decades and model these changes digitally. “Ideally, this will enable us to make recommendations on long-term land and resource usage and help to improve the environmental conditions in agriculture, forestry and water management.” (THGA/Si.)

The Research Center of Post-Mining (FZN) at the TH Georg Agricola University (THGA), Bochum/Germany, has a broad field of focus. When it was established in October 2015, research focused initially on the perpetual tasks of the German coal mining industry: long-term mine water management, the management of polder areas and groundwater purification on former mine sites. In May 2019, the FZN added “geomonitoring in post-mining” to its research profile. The aim of this research is to develop innovative technical systems for the integrated monitoring of post-mining activities. The FZN celebrated its fifth anniversary in 2020 and since then has expanded its research further to include “materials science for the preservation of industrial heritage” and “reactivation and transition”.

As a result, the FZN has all the skills and expertise required to help make the post-mining era sustainable, environmentally friendly and economically successful. The aim is not only to preserve this ever-growing expertise, but also to apply it in new ways. The interdisciplinary team shares its findings at specialist conferences and in working groups, and also makes the information available to the public in the form of studies and publications. Since 2019, the FZN’s final reports and studies have also been available as part of its scientific series “Reports on Post-Mining,” which is self-published by the THGA. Two reports have been published to date. In these reports, the authors examine aspects of the mine water rebound process in underground mines.

Volume 1 “Evaluation of Mine Water Rebound Processes” (Melchers et al., 2019) compiles the diverse experiences gained in the long-term and environmentally friendly management of mine water in selected European coal-mining districts (Figure 1). The hydrogeological, mining and water management aspects are systematically evaluated and site-specific features identified. The findings help to illustrate the mine water rebound process and aid understanding. Building on this, volume 2 “Model-Based Sensitivity Analysis of System-Determining Factors”(Westermann, 2000) provides an overview of the key natural and anthropogenic influencing factors. The scale of the effects of certain factors is determined for three underground mines by way of an example and applied to other sites. The findings are used to help actively shape the mining life cycle and plan ahead for the post-mining era.

The plan is to continually expand the scientific series “Reports on Post-Mining” with the FZN’s wide-ranging findings on the topics of mine water management, geomonitoring, materials science and structural change measures. Previous and future reports can be accessed free of charge in digital format at www.nachbergbau.org/berichte-zum-nachbergbau. (THGA/Si.)

Our underground is on the move. However, the shocks are often so small and spatially restricted that they are only detectable for very sensitive sensors. Even where mining was once conducted and people interfered with the natural geology and deposits, it may subsequently cause microseismic shocks. Paloma Primo, scientist at the Research Center of Post-Mining (FZN) at the TH Georg Agricola University (THGA), Bochum/Germany, pursues these mini-movements. In the new research project “PostMinQuake”, the expert examines how they occur exactly, identifies particularly endangered structures and develops a long-term risk management system for affected regions (Figure 1). To this end, she works closely with many European partners. Because also in the Czech Republic, Poland and France the post-mining period should not become a “nail-biting affair”. “The joint project is just as complex as the circumstances underground”, says Primo. “Our investigations go beyond the simple connections between seismicity and the geological activities in the decommissioned coal mines partly filled with water.”

Experts from various disciplines are working together in the project, including surveyors, geotechnical engineers or hydro-logists. Together they monitor the geological dynamics in the respective test areas, which have been changed by coal mining – in Germany this is mainly the Ruhr area, the Ibbenbüren and Aachen mining districts. “In these areas we document microseismic activities underground roughly once a week. There are also records from the past, which we analyse and put into context.” Primo obtains her data from the Geological Survey NRW, RAG Aktiengesellschaft, the Institute for Geosciences and Natural Resources (BGR), as well as seismological stations at the Ruhr-University Bochum (RUB). “At these stations we can determine time, size, place and depth of the event.”

The experts are pursuing an important common objective, explains Primo: “With our research we want to guarantee long-term safety, create transparency and inform the public. Because every municipality and every former mine operator should have sound knowledge of the processes that take place underground. When it comes to the topic of ground movements there are many fears and misunderstandings about what microseismic events are and the effects they can have.” Therefore, the main objective of the project is to gain a better understanding of the mechanisms of microseismic events after mining and create plans for the long-term monitoring of the soil after mining.

What external factors cause the micro-shocks? What factors can be used to realistically simulate the impacts on the PC? And how can satellite images help to properly interpret the data acquired from underground? “We’re talking here about vast amounts of data, which first of all we have to standardise in order to make it comparable and then be able to evaluate it using the latest methods”, says Primo. Over the next three years the project team will develop a reference database from the findings for European areas after mining. The research should also help to develop new monitoring strategies and interpretation methods for areas with increased risk of earthquakes. The project is part of the EU-financed Research Fund for Coal and Steel (RFCS). (THGA/Si.)

Construction sites, closures, narrowed lanes: Since the end of March 2020 the patience of drivers who use the Dortmund/Witten motorway junction is being tested. But the remediation work on the A44 is urgently required, says Cedric Kamgaing Kamdom: “ Most recently we detected and backfilled a hollow space, which was around 10 m high and 3 m wide – roughly as big as a single-family house. And it was just below the road surface”, explains Kamgaing Kamdom, who works as a project manager at the responsible engineering firm arccon -Ingenieurgesellschaft mbH, Gelsenkirchen/Germany. The experts have now piped around 800 t of concrete mix into the holey underground in order to secure it. This corresponds to around 30 full semitrailers.

The near-surface cavities originate from olden times: At one time the miners here mined the -Vereinigte Wiendahls-bank mine through the ground. The mine closed down in 1924. The available data is sparse.

“The plans for the deposits are over 100 years old. This does not make it any easier for us.” Apart from that, there is also the so-called illegal mining, which is not recorded anywhere. You cannot simply drill straight over it, explains Kamgaing Kamdom: “Our most important task is to optimally detect the suspected cavities in order to save time and costs.”

And the concrete mix needs to be carefully chosen, depending on the nature of the cavities and loose zones. At the beginning of such a project is a basic evaluation, during which old mine plans are also evaluated. They can provide guidance on surface openings, old tunnels or working areas of a mine. Following this basic research, if necessary exploration, safety and safeguarding works are planned, tendered and executed in the form of drilling and backfilling at extreme depths.

Specialist knowledge that Kamgaing Kamdom acquired in the course of his studies. Five years ago he came from Cameroon to Germany and decided to study at the TH Georg Agricola University (THGA) in Bochum. He acquired a fresh perspective in the master programme “Geological Engineering and Post-Mining”: “I was unfamiliar with the labour market beforehand, but did know that the coal mining sector in Germany was due to end in 2018 and that then certainly people who are knowledgeable in post-mining would be recruited”, says Kamgaing Kamdom, who already studied geosciences in his home country.

He turned out to be right. Experts at the interface between mining, surveying and geotechnical engineering are not only in demand here in Germany, but also internationally. Because the mining of raw materials leaves its mark worldwide (Figure 1). Special safety and restructuring measures are required in order to manage the risks at former mining sites. The master programme at the THGA, which is the only such programme offered in Germany, trains engineers to responsibly plan and execute the complex processes of mine closures and the aftercare. This also includes intelligent after-use in the affected regions.

For Kamgaing Kamdom the language was initially a little obstacle. “Especially in the lectures I had to be very attentive, but the good contact with other students and the lecturers made things a lot easier. The course is also very practical and you are out and about on the road a great deal”, says the graduate.

And what’s happening now on the A44? “We are currently on schedule. But there is still one part to come.” Here there may be more unexpected challenges hiding somewhere for the engineers, but Kamgaing Kamdom is confident: “When we have completed our work, probably in summer 2021, we are forever on the safe side.” Ideally, for drivers this means: For starters, peace and quiet on the A44. And for Kamgaing Kamdom: Off to the next construction site! Because the post-mining era is significantly longer than the mining era itself and brings full order books also in the future. (THGA/Si.)

Save the date: Bereits zum sechsten Mal veranstalten die Technische Hochschule Georg Agricola (THGA) und die Bezirksregierung Arnsberg ihre gemeinsame Fachtagung. Thema diesmal: „Grubenwasser – analog gedacht, digital diskutiert!“ Dazu treffen sich die Expertinnen und Experten dieses Mal ausschließlich online!

Wie gelingt ein verantwortungsvoller Umgang mit den Folgen des Bergbaus? Und welche Perspektiven bietet die Nachbergbau-Ära für Mensch und Umwelt? Diese Fragen stehen im Mittelpunkt der kommenden Fachveranstaltung NACHBergbauzeit in NRW. Die THGA und die Bezirksregierung Arnsberg als Bergbehörde NRW führen die interessierte Öffentlichkeit sowie Expertinnen und Experten der Branche zum intensiven Themenaustausch zusammen. Der Dialog im März 2021 findet erstmals als Online-Konferenz in der Zeit von 10:00-13:00 Uhr statt. Sie sind hiermit herzlich eingeladen, sich an der digitalen Diskussion zu beteiligen.

Themen 2021:

• Welche technischen Herausforderungen ergeben sich beim geplanten Grubenwasseranstieg in den ehemaligen Steinkohlerevieren an der Ruhr, der Saar und in Ibbenbüren?
• Grubenwasseranstieg europaweit: Was können wir von unseren Nachbarn lernen?
• Welche Methoden eignen sich zur langfristigen Überwachung von Bergbaufolgen?
• Wie lassen sich die Erkenntnisse aus der Steinkohle auch auf andere Bergbauzweige übertragen?

The history of mining is long – but the history of post-mining will be much longer. For five years now the Research Center of Post-Mining (FZN) at the TH Georg Agricola University (THGA) in Bochum/Germany has been attending to the issues that emerge as mining activity ceases. As the world’s first institution, it takes a comprehensive look at the post-mining era. The scientists are examining not only the tasks that mine water or former mining areas leave behind. They are also developing modern monitoring methods, advising affected regions on the structural transformation and trying to preserve the industry culture.

“The challenges of post-mining are complex, that’s why we are also becoming increasingly complex”, says Prof. Ulrich Paschedag, Head of FZN (Figure 1). “Since October 2015 we have been pooling the necessary know-how to shape the consequences of mining in a technically, economically and environmentally friendly manner.” In the interdisciplinary team around 40 independent experts in mining, geology and geo-technology, hydrogeology, chemistry, electrical engineering, materials science, land development, mine surveying and economics, all work closely together. This is the core around which a broad network has been established, nationally and internationally.

In the beginning the focus was still on researching the so-called perpetual tasks of the coal mining industry, but the FZN has been expanding its focus to this day. From the integrative approach come the four research areas: perpetual tasks and mine water management, geomonitoring in post-mining, materials science for the preservation of the industrial heritage, as well as reactivation and transition.

The experts are currently developing the scientific bases for an ecologically and economically compatible mine water ascent. The experiences from other European territories, in which such processes have already taken place wholly or partly also help. “The mine water rise is technically controllable”, says Prof. Christian Melchers. “Now it is about designing sustainable water management systems within the closed mines. Only then can the water resources in the former mining landscapes be reshaped in a near-natural way”, states the expert. The findings can also be transferred to other mining activities such as lignite or the gas and oil industry.

In the future geomonitoring will be about monitoring the impacts of mining over the long term using modern technology. “For this we must skilfully connect lots of information – like with a puzzle”, states Prof. Tobias Rudolph describing his area of research. Satellite data, historical maps, soil samples or multispectral aerial views with the drone are used here. “From these we can draw conclusions, e. g., about soil changes and detect changes in the vegetation.” In close cooperation with materiaIs scientists at the German Mining Museum (DBM) in Bochum, new methods are also being developed at the THGA to slow down or ideally stop ageing processes. The post-mining experts are helping to preserve the industry culture such as old winding towers or blast furnaces.

The cutting-edge research in the area of post-mining is in demand worldwide. More and more countries are interested in a far-sighted approach for handling active and former mining sites. The knowledge from Bochum also helps to make future mining processes more environmentally friendly. The FZN is in constant dialogue with its many international partners. It will also remain challenging in the future. “We are concerned with highly complex questions and interrelationships that take place in locations that are frequently still difficult to access. Underground, e. g., in places most people have never been to, and which will soon become inaccessible to all of us”, says Prof. Paschedag. “This is the reason why we, as scientists, have to make a special effort to formulate our post-mining findings in a way that can be generally understood by everyone.”
(THGA/Si.)

RAG Aktiengesellschaft, Essen/Germany, started to digitise abandoned surface openings, shafts and mining galleries of the coal mining sector via the Sigfox-0G network. There are around 60,000 in North Rhine-Westphalia alone. The aim of this IoT connection is the continuous monitoring of changes in real time in order to increase protection against sinkholes and reduce the effort of on-site inspections. The Sigfox–0G-based mining shaft monitoring system, which is also used for long-term documentation, has been designed by the Research Center of Post-Mining (FZN) and the Electrical Engineering/Information Technology and Industrial Engineering research sector of the TH Georg Agricola University (THGA) in Bochum/Germany and developed to series production in cooperation with the RAG (Figure 1).

The 0G-based remote monitoring system which is operated by a solar generator comprises pull-wire switches and a microcontroller with radio transceiver, which transfers the data via Sigfox-0G networks to a monitoring cloud. The sensors monitor, e. g., the vertical movement of the filling column of an old mine shaft. The data collected via Sigfox-0G network can be shown in the cloud for monitoring purposes and in the event of an alarm can be automatically sent to a predefined message chain by SMS and e-mail.

“It is necessary to constantly monitor the over 5,200 km² hard coal easements in our area of responsibility which have around 7,200 former surface openings because sinkholes are possible at any time in a section of around 100 km². Therefore, around 6,000 inspections are carried out every year in order to be able to take preventative action in good time. To minimise these on-site inspections and for real-time monitoring of any changes, selected surface openings are now also constantly monitored via a Sigfox-0G network connection”, says Frank Wollnik from the Site and Geo Services Division of RAG.

“The Sigfox-0G solution for shaft monitoring is an element of the so-called Mineberry system, which works completely independently and is solar-operated and is suitable for almost every type of old mining objects thanks to the modular structure. In order to implement the cloud connection of our remote monitoring solution in a manner that is cost-efficient, long-lasting and maintenance-free, we connected proven sensor technology to the innovative Sigfox-0G network. And as it can be used worldwide without any roaming charges, our solution can also be used worldwide”, explains Prof. Bernd vom Berg, Head of the Laboratory for Electrical Measurement and the Laboratory for Microprocessor Technology at the THGA.

“The RAG monitoring system is an excellent example of the remote monitoring of things and states, which up to now could not always be given special attention because it was too expensive or too energy-hungry to record all this data in real time. However, with Sigfox 0G real-time monitoring of even the simplest objects and states is possible. In the case of mining, it is easy to imagine that there are many control points worldwide, which can be monitored via a Sigfox-0G network. Especially because after the fossil-fuel phase-out no more money is earned, cost-efficient and low-maintenance data communication channels like Sigfox-0G offers are particularly important”, explains Stéphane Pâris, Technical and Network Director at Sigfox Germany.

The 0G controller is installed aboveground outside the possible Ex zone for the remote monitoring system for surface opening monitoring, whereas the Ex-protected sensors are installed in the shaft. As radio signals can be transmitted via the Sigfox-0G network across many kilometres, their use is also possible in areas with a poor mobile phone connection. The controllers can also be operated for many years without changing the batteries thanks to the battery-saving radio technology. Installations in the equally radio-critical underground environment can be found in the water supply network of the city of Antwerp. However, prerequisites for extensive underground installations are repeaters, which must be positioned every 3 to 5 km. (THGA/Si.)

On 15th May 2020, the TH Georg Agricola University (THGA), Bochum/Germany, appointed Kai van de Loo as honorary professor. Prof. van de Loo has already been passing his knowledge on to budding industrial engineers at the THGA for many years in his role as lecturer. From 1992 to May 2020, he worked for the German Coal Association (GVSt), Essen/Germany, in various functions and roles. In future, Prof. van de Loo will also be contributing his expertise to the Research Institute of Post-Mining (FZN) at the THGA.

RAG Aktiengesellschaft, Essen/Germany, tested methods for further reducing PCB in pit water at pilot facility level in Bergkamen and Ibbenbüren. The initial results from this series of tests are now available. The investigation into the PCB content takes place at the margin of detectability in the trace substance range. The analytical process being used here for the first time needs further development. At the same time, project manager Christoph Schabronath emphasises that: “The environmental quality standard for PCB in water is being adhered to at both the Haus Aden and Ibbenbüren sites.”

RAG broke new ground with this project and exceeded the legal requirements. Both the systems engineering and the analysis in the trace substance area were challenging. The task was to filter the smallest traces of PCB out of a large volume of pit water and to analyse it.

In North Rhine-Westphalia, RAG operated a pilot facility on container scale for removing PCB from pit water at the Haus Aden site, followed by Ibbenbüren (Figure 1). Further developed technologies and operating methods from drinking water preparation were used, i. e. single- and multi-layer filters made from quartz sand and anthracite coal in the pit water side stream.

Schabronath explains: “The pilot facility ran smoothly at both sites. However, the examination of the PCB content took place at the margin of detectability in the trace substance range.” Reliably determining such small traces of a substance and assessing the results is extremely challenging, and requires experience and a procedure adapted to the specific case at hand.

Due to the low concentration of PCB in the pit water, the results were unclear and it was not possible to eliminate uncertainty in the analysis. With such minimal traces, parallel investigations into the background presence of PCB in air and water are necessary.

At the end of 2019, an expert group consisting of ministries, authorities, surveyors and scientists met to assess these results. This group of experts also sees a need for further research. RAG has committed to further developing the analytical method within the framework of a doctorate in cooperation with the TH Georg Agricola University (THGA) in Bochum. (RAG/Si.)