Department of geomechanics and mining research
Main research topics
The department investigates natural and anthropogenic impacts on geomechanical processes in the Earth crust. The problems of underground mining, underground civil engineering, some geotechnical and geomechanical problems and the problems of underground space ventilation are solved both for obtaining scientific results and solving practical problems. The solution of stabilising natural and artificial underground openings serves to ensure safe operational conditions.
- Investigation of stress and strain states in rock masses
This research deals with distribution, magnitude and orientation of natural and induced stress fields in relation to geology, tectonic situation, anthropogenic activities in rock masses and analysis of stress state manifestation. Research is aimed at the investigation of a real rock mass stress field and its changes by hydrofracturig. It uses a conical gauge probe and gauge rock bolt for geomechanical monitoring, measurement of underground opening deformation and analysis of the stability states. Application of mathematical models is used in geomechanics and geotechnics for investigation of processes in rocks and soils from the engineering point of view. Dynamical geomechanical events in rock mass and the influence of geological and anthropogenic underground activity on subsidence of the Earth surface are also studied.
- Investigation of air flow in underground openings
This uses mathematical modelling of gas flow in specific conditions to compute ventilation in the underground galleries with the optional use of machine cooling. Modelling and calculation of the spread of the combustion products of mine fires into the mine gallery system is carried out along with modelling of mine fire expansion in goaf and modelling of gas flow in spoil banks.
- Destress blasting in rock masses and the evaluation of its effects
Destress blasting is the most important active rockburst measure in the Czech part of Upper Silesian Coal Basin. Destress blasting is carried out in the coal seam and its adjacent rocks causing overburden and/or in the underlying rocks. Evaluation of the efficiency of destress blasting in the sense of stress release in rock massifs is an important part of rockburst prevention. The present system of efficiency evaluation is assessed on the basis of seismological monitoring. Our research is focused on usable parameters from seismological monitoring (registered seismic energy, magnitude, maximum volume changes in focal area), natural conditions and technical parameters of realized destress blasting.
Important scientific achievements
- Improving of rock mass properties by grouting means
A wide range of information of the methods and results of (goal-) directed influencing of rock mass properties by chemical grouts has been investigated. Particularly increasing the safety level and stability of underground openings in conditions of increased static and dynamic stress has been studied. Reinforcing the low strength but brittle layers of a rock mass around underground openings is characterized by qualitative modification of the deformational properties of arising in geocomposites. It vents itself in a considerable increase of cohesion and rise of residual strength over the ultimate strength of rock material. Likewise, by using suitably chosen grouts, it is possible to treat existing joint systems in rock masses and to guarantee increased cohesion even in the case of significant deformations. It is also possible to reach (in macro-dimension) a rehabilitation of material strength even up to the original strength of the intact material. The real verification of the methods and technologies used in rock mass reinforcement by chemical grouts was done by in-situ experiments in coal mines. The field experiments document the real possibility and effectiveness of chemical grouting for goal-directed material improvement of rock mass properties in practice. Especially good reinforcing was achieved in combination with the anchoring elements.
- Induced stress field on the background of primary stress
influenced by structural - geological inhomogenities
The unique set of stress measurements in the Czech part of the Upper Silesian basin has been extended. The direction of the major principal stress is parallel to the geological structures, i.e. the tectonical faults but also the folding structures. The major principal stress on average achieves the value of the overburden load, the minor principal stress is 0.5 - 0.6 times this. We created a large 3D mathematical model of the area containing detailed information about the mining and geological situation in the 2nd block of the CSM Colliery. The verification of hypotheses which clarify the stress field distribution in the area, proved that the distribution of horizontal stress in the area at a depth of 1 km below the surface is primarily induced by the overburden load and formed by the structural and geomechanical properties of the area. The additional stress factor caused by a shift of the Carpatian nappes has not been verified in the whole area of study. The influence is only accepted in the east part of the monitored area adjacent to the Tesin fault. For measurement of the induced stress changes by an overcoring method was used. Aprototype of a specific piece of equipment was developed, which is unique in the Czech Republic. The main idea is based on application of the conical tensometric head, which makes the measurement of whole stress tensor in a single position possible. Wireless recording simplifies and facilitates the observation of the overcoring process.. The simplified variant of the probe is also applicable for long term monitoring of stress changes.
- Mathematical modelling of mine fire effect on air flow and propagation
of mine fire products within the mine ventilation network
In spite of a large expansion of interlocking security and measurement technologies as well as the development of the application of materials with considerably reduced inflammability, a potential risk of mine fires in any part of an underground mine cannot be excluded. The risk of mine fires is very dangerous for mine personnel not only due to the development and propogation of mine fires which contain toxic substances (which are entrained into other mine workings), but also due to the fact that changes in the quantity and direction of volumetric air flow within the mine ventilation network occur by the effect of heat generated by mine fires. The main aim of the project was to develop a mathematical model, which would explain the impact of mine fires on air flow and on propagation of mine fire products within mine ventilation network. The mathematical model was created in the form of a computer programme with a synoptic graphic editor to representventilation branches and their basic parameters such as volumetric through-flow, depression, temperatures, and chemical composition of the mine air.
- New methods for the prognosis of surface subsidence affected by underground
exploitation of ore vein deposits of the Rozna type
A prognosis of thedevelopment of subsidence depressions above ore veín deposits of the slab-like variety with adjacent solid rocks (deposits of the Rozna type) mined by underground method is a very specific problem which has not been satisfactorily solved until now. In connection with long-term surveying observations a newly conceived mechanism for the genesis of a subsidence depression above the uranium deposit of Rozna was described. Based on this, geomechanical model of the depositional situation is elaborated which then enables us, by means of mathematical modelling of surface subsidence development, to predict the development of subsidence depressions both in the phase of deposit mining and in the period after the termination of the mining works.
- Compilation of knowledge of rockbursts in coal mines and the means
of minimising their impacts
The knowledge of the main causes of rockbursts was collected and analyzed on the basis of detailed studies of the rockbursts in the Ostrava-Karvina coal basin from 1989 and by means of mathematical modelling. Means of improving the dynamic bearing capacity which supports the exposed part of the mine was studied to minimise eventual rockbursts. The proposal of prevention measures for decreasing the risk was partly supplemented by the new decree No. 659/04 Sb. issued by the Czech Mining Authority and partly by other legislative changes in Working rules and Methodical principles.
- Evaluation of the effectiveness of rock blasting for stress release
in the rock massif (monograph)
Rock bursts are a very dangerous phenomenon in Czech part of the Upper Silesian Coal Basin (USCB). Destress rock blasting in overlaying strata is one of the most important measures used to prevent rock bursts. The main goal of this measure is to disintegrate competent rocks in the overlaying strata and comsequently release stress in the vicinity of excavated coal seam. Qualitative and quantitative stress release is very important in the evaluation of rockburst prevention. The monograph sums up existing knowledge in destress blasting in USCB conditions. The most common method of evaluating the effect of stress release based on seismic monitoring data is described. Seismic effect is calculated as a ratio of registered seismic energy to theoretic energy released by explosivesduring blasting. Contemporary systems of seismic effect evaluation are discussed. Relevant data obtained from seismological monitoring over a period between 2000 to 2008 was analyzed. On the basis of the analyzed data (about 900 uses of destress blasting) a new system for evaluating the effect of stress release was proposed. The new system uses registered seismic energy and magnitude data along with statistical analysis of the data set from destress blasting.