Underground experimental sites and laboratories are rare and offer unique opportunities for research, development, innovation, education and training, among other usages due to their special boundary conditions. Each underground facility is highly unique in its geological and geophysical characteristics. These sites can be either dedicated infrastructures built for specific usage or mines and parts of mines freed from underground extraction. Since they are usually isolated from environmental influences and, conversely, shield experiments as far as possible from the environment, they offer unique research conditions and possibilities compared to surface laboratories.

However, the sustainable operation of such underground experimental sites is not an easy task. Hence, to foster and accommodate the use, scientific collaboration and interdisciplinary scientific research among European underground research facilities, a specialized association has been set up by a number of European partners under the name European Underground Laboratories Association EUL.

This association defines its purpose by forming a network between the underground laboratories and client organizations from business, science and administration sectors. The goal is to bundle and develop existing competencies, and thus providing a common platform for members and prospective researchers and costumers on order to share and exchange information and experience, and in turn to contribute to the development and implementation of new research projects. As an Europe-wide and internationally active association comprising EU members and non-members, EUL also supports and promotes European integration and international cooperation.

This paper provides an overview over the structure and the organisation of EUL, its member institutions and associated underground research laboratories as well as the possibilities the association may offer for its members and interested partners in the fields of:

• providing a comprehensive overview of the research possibilities and conditions at the different underground sites to clients and the public
• infrastructure development at the research locations and improvement of research conditions in each underground facility
• execution of joint research proposals and respective project planning
• setting up and extending the spread of advertising materials and publications
• education and training of students, researchers and professionals,
• enabling the exchange of researchers, professionals and/or students among partnering facilities

How to cite: Mischo, H., Fuławka, K., and Joutsenvaara, J.: European Underground Laboratories Association EUL – An International Partner for Underground Research Opportunities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7730, https://doi.org/10.5194/egusphere-egu21-7730, 2021.

Being at the phase of entering the new digital era, the mining industry is constantly facing challenges utilizing the introduction of data-oriented and multi-criteria decision-making concepts, demand for real-time solutions and need for experienced staff. Hence, lifelong updating of knowledge and skills of mining experts has become increasingly important and recognized worldwide as a challenge for developing a sustainable mining sector. It is also well acknowledged that an interdisciplinary understanding of mining professionals over the integrated mine value chain is expected to optimize the efficiency of operations and in turn, enhance the feasibility of mining projects.  Given also the nature of the vast majority of mining activities, practical know-how is of great importance. There are, however, very few opportunities around the world for hands-on training in real mining conditions, and even less so at actual mine sites.

Hence, the idea of transforming abandoned or closing mines into training facilities is becoming more and more attractive among mining industry professionals, academics and researchers. Nevertheless, the theory is far from practice, and such an endeavour is by no means easy. In this concept, the Pyhäsalmi Cu-Zn Mine, in northern Finland is shortly to cease its operations. New activities are being investigated for the post-usage of the mine site. This in mind, Callio has been established as an umbrella organization to offer opportunities for business, development and research projects in the existing unique mine environment. Accordingly, the MINETRAIN project was launched in 2018 to investigate the possibility of utilization of the Pyhäsalmi Mine site for the education of mining experts and students. As a training and educational facility, the Pyhäsalmi mine will provide a globally unique environment, with training possibilities covering topics over the entire Mine Life Cycle; from exploration to mine closure.

To test the feasibility of Pyhäsalmi mine as an educational and training site, two pilot training courses have been developed during the last two years in the context of MINETRAIN, namely Mine Life Cycle and Digital Life of a Mine. The participation was tremendous, and the feedback received from the trainees has been highly positive; the obtained worldwide attraction strongly implies a great interest among mining professionals in practical education. Hence, in this paper, the challenges faced and the lessons learnt from the organization of these pilot courses are discussed with respect to the viable transition of Pyhäsalmi mine to an educational and training underground facility.

How to cite: Barakos, G., Luolavirta, K., Joutsenvaara, J., Luukkanen, S., Puputti, H. J., and Mischo, H.: The MINETRAIN project: Lifelong Learning opportunities for mining industry related professionals in real-life underground mining conditions; Dealing with the aftermath of two innovative pilot courses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5121, https://doi.org/10.5194/egusphere-egu21-5121, 2021.

Abstract. Abandoned mines are unique underground facilities due to their unique conditions. Mined-out mine can be used as a museum or scientific and technical research site. Depending on specific mine conditions the after-use purposes can vary. The former Kohtla oil-shale mine, located in the eastern part of Estonia, was closed 10 years before the idea to re-open it as a mining museum. Now old Kohtla mine is used as an underground museum to present for local people and tourists how mining works were carried out in the past (Estonia has 100-year-old experience in oil shale mining) and which methods are still in use. Besides mining, it also shows ventilation and water barrier solutions in the mine. 

We present an overview of abandoned mine new challenges to be a safe environment for tourists and as a future research center. The project team had a challenge do design: 

• Renovate underground railway, walker’s platform’s, design and establish new roof supports 
• New railway platform, stations for tourists, water barriers (3)
• Ventilation duct and walls (8), new ventilator;
• Closing the workings which are not needed.

Designing was challenging but not the most difficult part of the project. More complicated was to find a competent builder for the underground museum. Renovated and re-ventilated mine was opened in 2012 and today museum is one of the most visited places by the tourists in the eastern part of Estonia, because of its uniqueness. 

Besides as a museum, it can be used as a testing site for researchers, because its former infrastructure and facilities have remained. For example, 4 years ago Tallinn University of Technology used the museum area for the backfilling testing because the temperature and other underground conditions were suitable for room-and-pillar mining method backfilling tests. By using backfilling technology, environmental problems such as ground collapses can be avoided and production residues can be reused. As a result of the research, it became clear which ashes of Estonian power plants and the oil industry are suitable for the backfilling technology in terms of physical-mechanical and chemical properties.

In addition, we will highlight the best design practices and experiences that have implemented in order to improve old mine everyday working conditions as a museum. These best practices are usually more than the national laws and regulations have requested and they are deeply connected with practical experiences. It meant a lot of collaboration in bringing the best know-how together by different stakeholders. 

How to cite: Kaljuste, V., Väli, E., and Paat, A.: Abandoned mine after-use as a museum and research site, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11540, https://doi.org/10.5194/egusphere-egu21-11540, 2021.

One of the most important parameters characterizing underground laboratories is natural background radiation. In underground locations, natural radiation mainly comes from the surrounding bedrock and used building materials. When selecting an underground site for research and projects, great importance is attached to the conditions prevailing there, which translates into the success of the activities carried out. Accurate measurements of natural radiation are therefore essential to guarantee the success of the project. As a part of the BSUIN (Baltic Sea Underground Innovation Network) project, such measurements were carried out in several underground laboratories. Although the BSUIN project ended last year, this research continues under the ongoing EUL (Empowering Underground Laboratories Network Usage) project.

Results of the in-situ measurements of gamma radiation and radon concentration will be presented. Additionally, laboratory measurements of radioisotope concentrations in rock and water samples from the studied sites were performed. The concentration of radioisotopes in water samples was obtained by using a liquid scintillation α / β counter and α spectrometry, while the concentration of radioisotopes in rock samples was measured with laboratory gamma-ray and α spectrometry.

A comparison of the obtained results of natural background radiation with other underground locations will also be presented.

How to cite: Szkliniarz, K.: Characteristics of natural background radiation in selected underground laboratories BSUIN and EUL projects., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3030, https://doi.org/10.5194/egusphere-egu21-3030, 2021.

The BSUIN project conducted pilot measurements to test methods for characterizing underground laboratories for natural background radioactivity (NRB). One of the components of NRB that requires specific measurement methods is the neutron background.
The goal of our team was to developing a reference setup for neutron background measurements.

Our idea was to build a setup for measuring neutrons as simple as possible, but not simpler. The price and
universality of the measurement setup are important parameters, but the reliability of the result is also very
important. It is because the neutron flux in underground laboratories is usually very low and it is easy to
make a mistake in interpreting of the results.

The basics of our method will be presented, as well as the assessment of possible measurement errors and the transactional experience gained during measurements at six different locations in four mines.

How to cite: Jedrzejczak, K., Szabelski, J., Kasztelan, M., Przybylak, M., Tokarski, P., Orzechowski, J., and Marszał, W.: Minimal setup for neutron background measurements - summary of the BSUIN project, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15218, https://doi.org/10.5194/egusphere-egu21-15218, 2021.

We examined the uncertainty of the resistivity method in cavity studies using a synthetic cavity model set at six-different depths. Conceptual models were simulated to generate synthetic resistivity data for dipole-dipole, pole-dipole, Wenner-Schlumberger, and pole-pole arrays. The 2D geoelectric models were recovered from the inversion of the synthetically measured resistivity data. The highest anomaly effect (1.46) and variance (24400) in resistivity data were recovered by dipole-dipole array, while the pole-pole array obtained the lowest anomaly effect (0.60) and variance (2401) for the target cavity T₁. The anomaly effect and variance were linearly associated with the quality of the inverted models. The steeper anomaly gradient of resistivity indicated more distinct cavity boundaries, while the gentler gradient prevents the inference of the cavity boundaries. The recovered model zone above the depth of investigation index of 0.1 has shown relatively higher sensitivity. Modeling for dipole-dipole array provided the highest model resolution and anomaly gradient that shows a relatively distinct geometry of the cavity anomalies. On the contrary, the pole-dipole and Wenner-Schlumberger arrays recovered good model resolutions and moderate anomaly gradient but determining the anomaly geometries is relatively challenging. Whereas, the pole-pole array depicted the lowest model resolution and anomaly gradient with less clear geometry of the cavity anomalies. At deeper depths, the inverted models showed a reduction in model resolutions, overestimation in anomaly sizes, and deviation in anomaly positions, which can create ambiguity in resistivity model interpretations. Despite these uncertainties, our modeling specified that the 2D resistivity imaging is a potential technique to study subsurface cavities.

How to cite: Doyoro, Y. G., Ping-Yu, C., and Puntu, J. M.: Uncertainties Analysis of Electrical Resistivity Tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-340, https://doi.org/10.5194/egusphere-egu21-340, 2020.

The ore mining area of Freiberg is located in the federal state of Saxony in the east part of Germany and is characterized by hydrothermal ore mineralization.

The present petrophysical study concentrates on three different rock types from the research mine “Reiche Zeche”. The set of samples contains rocks from the metamorphic host rock - Freiberger Gneiss (FG), from a hydrothermal alternated gneiss (hG) and from a pyrit-galenit rich ore vein (ore). The investigations include the determination of density and porosity as well as laboratory measurements of the Spectral Induced Polarization (SIP) in the frequency range from 10^-3 to 10⁴ Hz. Furthermore, measurements of the magnetic susceptibility and P-wave velocity were performed.

For the determination of P-wave velocity by ultrasonic measurements, the rock samples were cut into cubes (5 cm x 5 cm) under preservation of their spatial orientation. The sample set contains 17 cubes (FG - 8 cubes, hG -3 cubes and ore – 6 cubes).

The determination of the complex resistivity was performed in a SIP – measuring cell on cylindric plugs with a length of 3 cm and a diameter of 2 cm. For the SIP-measurements 19 plugs (FG – 11 plugs, hG – 2 plugs and ore – 6 plugs) were available.

Density and magnetic susceptibility measurements were performed on 10 samples of crushed material for each rock type.

The data sets of complex resistivity and P-wave velocity measurements from rock samples of the metamorphic host rock and the ore vein were analysed with focus on possible anisotropic behaviour.

How to cite: Graffmann, L., Sonntag, M., and Börner, J.: Petrophysical study of different rock types from the mining area of Freiberg, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14399, https://doi.org/10.5194/egusphere-egu21-14399, 2021.

The STIMTEC and STIMTEC-X hydraulic stimulation experiments are designed to investigate hydro-mechanical processes controlling the enhancement of hydraulic properties in deep geothermal projects. We combine periodic pumping tests, high-resolution seismic monitoring, structural analysis and mine-back drilling into stimulated volumes in an effort to improve near-real-time monitoring, phenomenological models of the hydrofrac/hydroshear process, and prognosis strategies. The ongoing experiments are located at the Reiche Zeche underground laboratory in Freiberg, Saxony/Germany, at a depth of about 130 m below surface in strongly foliated metamorphic gneisses.

The most recent field campaign and initial phase of STIMTEC-X in October 2020 involved eleven local stress measurements in three existing boreholes, previously used for monitoring purposes, with varying orientations and lengths. We hydraulically tested nine previously stimulated intervals and performed eight dilatometer tests in previously stimulated and new intervals to determine deformation characteristics of induced hydrofracs and pre-existing fractures. We monitored these operations in real-time using an adaptive, high-resolution seismic monitoring network comprising six acoustic emission (AE)-type hydrophones, six regular AE sensors and four accelerometers. Hydrophones were never installed before in combination with hydraulic gauges or the double packer probe used for localized injection as during STIMTEC-X. Hydrophones were optimally placed for each measurement configuration anew with at least one deployed in the direct vicinity (~3-4 m) of the injection interval to make best use of the existing infrastructure. This led to an improvement in detection and localisation of induced AE events. A series of active seismic measurements allowed us to establish the polarization, amplitude sensitivity, detection ranges, resonance frequencies and suitability to detect S-waves of the hydrophones. Good signal to noise ratios were recorded for distances up to 17 m. The range of incidence angles, including incidence angles from the opposite direction, in which the sensor is facing, was obtained that can be used for magnitude determination.

A circulation experiment between the injection borehole and two newly drilled boreholes of 23 m and 30 m depth as part of STIMTEC-X is anticipated for March 2021. Here, we present lessons learned from seismic monitoring the STIMTEC and STIMTEC-X hydraulic stimulation campaigns and highlight the advantages of using adaptive and flexible networks. We present an overview of the STIMTEC-X experiment and first results addressing the heterogeneity in stress and deformational behaviour seen throughout the anisotropic reservoir.

How to cite: Boese, C., Kwiatek, G., Dresen, G., Renner, J., and Fischer, T.: Towards optimised seismic monitoring of hydraulic stimulations, the STIMTEC and STIMTEC-X experiments at Reiche Zeche Mine, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15326, https://doi.org/10.5194/egusphere-egu21-15326, 2021.

The polymetallic, hydrothermal deposit of the Freiberg mining district in the southeastern part of Germany is characterised by ore veins that are framed by Proterozoic orthogneiss. The ore veins consist mainly of quarz, sulfides, carbonates, barite and flourite, which are associated with silver, lead and tin. Today the Freiberg University of Mining and Technology is operating the shafts Reiche Zeche and Alte Elisabeth for research and teaching purposes with altogether 14 km of accessible underground galleries. The mine together with the most prominent geological structures of the central mining district are included in a 3D digital model, which is used in this study to study seismic acquisition geometries that can help to image the shallow as well as the deeper parts of the ore-bearing veins. These veins with dip angles between 40° and 85° are represented by triangulated surfaces in the digital geological model. In order to import these surfaces into our seismic finite-difference simulation code, they have to be converted into bodies with a certain thickness and specific elastic properties in a first step. In a second step, these bodies with their properties have to be discretized on a hexahedral finite-difference grid with dimensions of 1000 m by 1000 m in the horizontal direction and 500 m in the vertical direction. Sources and receiver lines are placed on the surface along roads near the mine. A Ricker wavelet with a central frequency of 50 Hz is used as the source signature at all excitation points. Beside the surface receivers, additional receivers are situated in accessible galleries of the mine at three different depth levels of 100 m, 150 m and 220 m below the surface. Since previous mining activities followed primarily the ore veins, there are only few pilot-headings that cut through longer gneiss sections. Only these positions surrounded by gneiss are suitable for imaging the ore veins. Based on this geometry, a synthetic seismic data set is generated with our explicit finite-difference time-stepping scheme, which solves the acoustic wave equation with second order accurate finite-difference operators in space and time. The scheme is parallelised using a decomposition of the spatial finite-difference grid into subdomains and Message Passing Interface for the exchange of the wavefields between neighbouring subdomains. The resulting synthetic seismic shot gathers are used as input for Kirchhoff prestack depth migration as well as Fresnel volume migration in order to image the ore veins. Only a top mute to remove the direct waves and a time-dependent gain to correct the amplitude decay due to the geometrical spreading are applied to the data before the migration. The combination of surface and in-mine acquisition helps to improve the image of the deeper parts of the dipping ore veins. Considering the limitations for placing receivers in the mine, Fresnel volume migration as a focusing version of Kirchhoff prestack depth migration helps to avoid migration artefacts caused by this sparse and limited acquisition geometry.

How to cite: Hellwig, O. and Buske, S.: Simulation of a seismic survey with combined surface and in-mine data acquisition for imaging steeply dipping ore veins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15350, https://doi.org/10.5194/egusphere-egu21-15350, 2021.