Geomechanics and mining research

The management of the post mining regions in Europe is important issue for the safety and economic reasons. The PostMineQuake treats the most important hazard related to unexpected ground motions. They may affect the surface stability, vulnerable structures and critical infrastructures. The main objective of the proposal is to deepen the knowledge of post-mining seismic events in relation to surface deformations, plans for long term monitoring of post mining lands, shaking-maps of the fluid-induced seismicity of European countries with coal mining legacy, transnational guidelines how to deal with and mitigate a hazard manifesting as seismic tremors in post mining regions.

The aim of this project was to obtain information on the spatial distribution of geological, geotechnical, geochemical and transport properties of the rock environment at various depth levels of the Rozna mine in the range of 12th to 24th floors. Moreover, it included understanding the influence of the tectonic zone on the properties of the rock environment, monitoring of the development of geotechnical and geochemical parameters with depth, definition of more homogeneous rock blocks in the range of accessible areas, description of the EDZ zone and deposit revalidation.

The aim of the project proposal is to find such a set of geotechnical and geophysical methods that delivers information about geological structure in both perpendicular and longitudinal direction with respect to an underground structure and about its time development and to find a set of methods which would contribute to a superior description of a geological structure of a rock massif in underground structure vicinity. The principle of this proposal is a development of such methods that provide insight into a rock massif. It is necessary to provide and verify techniques involving methods which use only measurements from a surface of an underground structure, as well as methods that work within a borehole - borehole or a borehole - underground structure surface system. For an interpretation of geophysical and geotechnical measurements it is useful to have a special software available. This software will allow to preprocess, to process and to complexly interpret measured data. Moreover, the dependencies between individual physical and geotechnical properties will be studied along with the properties dependency and development trends. Particular goals are: on the one hand to test a set of geotechnical and geophysical methods as wide as possible and to, in a form of resulting certified technology, determine and crosscheck the ones that best suit the solution of the given issue and on the other hand to develop a software tool for integration of results and additional processing of experimental measurements. An effort will be made to find a procedure for generation of such outputs that will be complex enough and, at the same time, understandable not only to specialists who are experts in the fields of geotechnics and geophysics but also to geologists, planners, employees of mining companies and specialists working in the state administration.

Modernization and expansion of a comprehensive system of observation of geophysical fields operated by geoscience institutions in the Czech Republic. This system consists of permanent observatories, mainly connected to global networks, local stations in selected areas that are important for long-term observation for basic or applied research, and mobile stations used for temporary measurements in selected locations, usually in large areas. international VIs and projects. 5 thematic sections: Seismology, GNSS and gravimetry, Geodynamics, Geomagnetism, Geological and geophysical databases.

The project has aimed at stable operation, development and upgrade of the network of geoscience observations operated by the Czech research institutions and universities. The system consists of permanent observatories (seismic, GNSS, magnetic, gravimetric geothermic and geodynamic) usually incorporated in global data networks, local stations or networks in areas significant in the long-term for basic research or applications and mobile stations which serve for repeated observations at selected points, or for field measurements, usually within the scope of large international projects. CzechGeo/EPOS is closely connected with the large European research infrastructure EPOS (European Plate Observing System). The priorities included user-friendly data access to global or regional data bases/repositories, increasing the number of stations with a real-time remote data access whenever possible, transmission of access to high-level products and integration of data in the frame of the Implementation Phase of the EPOS Project.The cooperation with EPOS was aimed at contributing to and taking advantage of the thematic and integrated core services.

Adjusting the probes for measuring stress in the rock mass for explosive atmospheres of gas and coal dust. Creating software for calculation of the complete stress tensor and its simple visualization around the probe.

The basic objective of the project is the development and operation of infrastructure and research-scientific teams created in the framework of the project Institute of clean technologies for mining and utilization of raw materials for energy use on the premises of the applicant VSB – Technical University of Ostrava and the participant Institute of Geonics of the CAS. The project preserves the built-up system of research teams interconnected with the laboratory infrastructure and is divided into two research programs that are interconnected and supplement each other.

The scope of Research Program 1 Multiphase Rock Environment is to obtain the knowledge of physical, chemical, isotopic, structural and mechanical properties of environmental components using modern instrument equipment, which basically increases the level of knowledge and possibilities of its generalization for the given geological conditions by means of mathematical modelling. This information is the basic precondition for the design of environmentally friendly technologies for the exploitation of mineral resources and also for the further utilization of rock environment.

Research Program 2 Environmentally Friendly Technologies is based on the findings from Research Program 1 and deals with oriented research and application solutions in the area of mining of energy raw materials, use of byproducts for the introduction of wasteless technologies to the mining of mineral resources, creation of conditions for minimization of safety risks based on the knowledge of causal processes, and with methods of valuation and influencing of the rock environment in connection with large projects under preparation that are concerned with the use of geothermal energy, permanent deposition of nuclear waste and underground storage facilities for energy raw materials.

Main research objectives which are solved in the Institute of Geonics are as follows:

• Properties and behaviour of geomaterials depending on their inner structure, type of loading and physical conditions. The comprehensive knowledge of petrological, chemical-physical and mechanical properties of rock environment is the basic precondition for the effective, safe and environmentally friendly design of technologies for the mining, processing and use of mineral resources or the driving of mine workings and the building of demanding underground and geotechnical constructions. The objective is to acquire knowledge of the influence of composition and character of inner structure of rocks and rock mass on their strength-deformation and transport behaviour and to acquire reliable and relevant data that can be used directly as input into numerical models and data for their experimental verification and inverse analysis.
• Intensification of effects of high-velocity water jets in the course of disintegration. The objective of solving this activity is to intensify the effects of high-velocity water jets using the physical phenomenon originating at the impingement of a droplet on a solid surface, because during the collision of a liquid moving at a high velocity with a solid, a short-term transient phenomenon appears, which is accompanied by a marked increase in pressure at the point of liquid impingement on the surface and can cause serious damage both to the surface and to the inner structure of materials subjected to the action of the falling liquid. For this reason, the solving will focus on the study of possibilities of influencing the flow before the nozzle to generate a jet utilizing the above-mentioned physical phenomenon for material disintegration.
• Development of changes in induced stress and deformation fields in underground utilization of a rock mass. In underground exploitation of mineral deposits and building of underground construction works, as a result of these activities, changes in the stress states in the rock mass take place. In the case of exceeding of relevant limit parameters of structural units of the rock mass, changes in stress can induce brittle fracture damage, which induces seismic events in affected areas. In complicated natural and mining conditions, this process may be accompanied by a sudden release of energy accumulated in the rock mass and the origin of anomalous geomechanical phenomena with manifestations in underground cavities. Significant stress and strain changes in the rock mass may also show themselves on the surface, play a significant role in the process of design of mine workings driven in the rock mass and affect the transport properties of the rock mass. The research objective will be to acquire findings in this area and to apply them to mining activity and underground construction.

Within the project, the Institute of Geonics has acquired several unique devices for the investigation of rock environment and development of geo-technologies. They are analytic devices, software, but mainly a servo-hydraulic testing system with a triaxial cell for testing THM (thermo-hydro-mechanical) properties of rocks, equipment for water jet application, and X-ray CT (computer tomograph) for non-destructive research of plane and space inhomogeneity in materials and for crack detection.

Owing to the new unique laboratory equipment, centre enables to start new research directions like in the laboratory of tomography, or substantially enlarge existing research directions - the laboratory of THM processes in rock mass or the innovation of the laboratory of pulsating high pressure water jet applications.

The project included a search section describing the foreign experience and knowledge from similar localities, as well as the implementation part for monitoring the change of the stress field during construction in the surroundings of URF Bukov. The solution of this project has a direct connection to the parallel project Complex Geological Characterization of URF Bukov spaces. It is described developed and deployed a distributed measurement system enabling to read data from different types of measuring sensors, store data and transmit them to a remote institution for processing and interpretation. The DMS mainly serves 6 CCBM probes and 4 triplets of measuring rock bolts for the stress field detection in the PVP Bukov site, as well as a series of sensors especially for monitoring the hydrogeological and thermal mode of the massif. The CCBO and CCBM stress measurements are carried out in this location following the excavation process. In the phase of the mathematical modeling of the stress field, sw tools were developed and subsequently used to determine the full stress tensor from the CCBO and CCBM probes and confronted with the determination of the stress field on base of the wall convergences of the mine crosscuts during its excavation. Safety level ranges have been set based on criteria of violations. Within the report the outputs of the 3D scanning application are described, both the BZ1-XII gallery of geo-laboratory itself and the BZ-XIIJ crosscut. The geophysical works were also carried out at the URF Bukov site in 2015-2017. Within a geophysical survey, measurement was carried out using the methods of electrical resistivity tomography (ERT) and seismic tomography (ST). Geoelectrical measurement was focused on the right side of crosscut BZ-XIIJ and gallery BZ1-XII of geotechnics laboratory, whereas seismic tomography used the borehole-crosscut system. The results of measurement provided pictures of the distribution of resistivity and the velocities of longitudinal waves behind the wall of the mine working,that is to say between crosscut BZ-XIIJ and borehole S3.

Considerable amounts of coal reserves are located in protection pillars that lie under built-up areas in actively mined regions in the Czech part of the Upper Silesian Coal Basin (USCB). The commonly used controlled caving longwall mining method is not applicable in these areas, because significant deformation of the surface is not permitted. For this reason, the modified Room - Pillar method (Roadway - Pillar) with stable coal pillars has been tested in order to minimise strata convergence. The four-year pilot project of the new mining method Roadway - Pillar was completed at the underground coal mine at a depth of 900 m, which is the deepest trial test of the method in the world . The monitoring included stress and deformation changes in pillars and roof strata, loading of roof and pillar rockbolts and deformation of the surface. The results of this wide-ranging monitoring of the stress-deformation state of RM, verified numerical models , and other analyses confirmed the stability of left coal pillars and effectivity of roof bolting in the conditions of highly stressed RM. Minimal subsidence effects on the surface were also demonstrated. These results, together with verified technological procedures, were the main sources for approval procedure of the new mining method by the mining authority. With regard to the mining depth up to 900 m, the results are significant not only from the point of view of Czech mining, but also worldwide.

Within the complex geotechnical characterization of the Bukov URF, the Institute of Geonics of the Czech Academy of Sciences in Ostrava carried out a series of laboratory and field works in order to provide a detailed description of the geotechnical and geomechanical properties and quality of the rock mass. The works included the determination and assessment of the physical-mechanical properties of the rocks sampled from the walls, boreholes and ground surface in the locality; the determination of stress state and deformation properties of the rock mass using the methods of hydrofracturing of borehole walls, Goodman Jack and CCBO, or CCBM; determination of the rock mass quality based on selected index geomechanical properties; periodic, long-term strain-gauge measurements and convergence measurements, and the assessment of the effect of technical and mine-induced seismicity on the rock mass of interest. The implemented set of research works was supposed to render a sufficient and integral whole of geotechnical and geomechanical knowledge vital for the subsequent implementation of extensive research experiments focused on long-term safety and technical feasibility of the future national deep repository of radioactive waste.

A thorough evaluation of the stress and structural record in granitic environments is essential for evaluation of the long-term safety of deep nuclear waste repositories located in such environments. The international project “Large-Scale Monitoring” (LASMO) leaded by Nagra was aimed at determining a comprehensive way to describe stress changes in granitic rock caused by large-scale unloading/loading of the rock mass. The experimental phase of the project was being conducted at the underground laboratory of the Grimsel Test Site situated in the Swiss Alps. The measurements and the subsequent monitoring of strain changes, along with the analysis of stress-strain relations and special studies focusing on internal anisotropy of rock provide important characteristics of the overall stress evolution in the investigated region, influencing the stability of the rock mass. The above mentioned subproject LASMO belonged among SURAO supported activities within the LASMO international project. The Institute of Geonics CAS, the Czech Geological Survey and the Institute of Rock Structure and Mechanics CAS collaborated on this task.

Involvement in this international project provided with important information for the eventual construction of the 3D stress models required for a thorough evaluation of the safety of the future Czech underground repository. The main aim of this subproject was to determine the general characteristics of rock mass behavior as a result of loading and unloading processes under the larger scale conditions of the underground repository.

The main objective of the project was to assess the degree of reproducibility of transport laboratory experiments with the results of the experiment larger scale (dm) and the possibility of subsequent implementation in the actual granitic rocks (in-situ experiment) and in models assessing the diffusion of radionuclides into the rock. The results can significantly contribute to reducing uncertainty quantification of transport parameters tracers in rocks, resulting from the simplification of the real processes using small sample sizes in the laboratory . At the same time the aim was to make a suitable apparatus or assemble a working methodology that would allow the transmission of information about the properties of rocks and processes running in them from the microscale (mm) into the real environment of the rock mass scale (tens of meters). Finally, the aim was to apply methodologies that could anable to achieve the objectives and that have been widely applied so far, for example use of special tracers or innovative modern analytical techniques.

The project was focused on the research of processes in rock environment, whose understanding was essential for long-term stability of deep repository of radioactive waste and long-term operation of underground gas storage reservoirs. The first part of the project was focused on experiments performed to study the THM processes in Underground laboratory Bedřichov, UEF Josef and some other localities. The second substantial part of the project covered development of software tools applicable in the process of complex assessment of particular locality in the context of planning radioactive waste disposal underground facility.

CzechGeo/EPOS was aimed at establish and operating the national node of Pan European project EPOS. The backbone of recent observing system in the Czech Republic forms permanent seismic, tidal, geodynamic, geomagnetic and geothermic observatories. The system was completed with local networks and temporary monitoring experiments. EPOS aimed to create a single sustainable, permanent and distributed infrastructure to achieve integration, increased accessibility and long term continuity and data archiving of geophysical monitoring data from networks in Europe and in the Mediterranean regions. Moreover, EPOS has introduce an innovative strategy based on merging within a single but distributed infrastructure data, in-situ observatories and laboratory experiments and high-resolution and high-performance computational tools bridging the gap between observational and geophysical modelling by linking advanced simulation technology and processing facilities directly to the observational data bases. EPOS has thus create a strongly competitive European research infrastructure providing radically new conditions and new horizons for solid Earth science research in Europe. CzechGeo has contribute to and profit from the EPOS achievements.