Recalling the body of experience gathered in the collieries of the Upper Silesian Coal Basin, the

increased risk of seismicity and rockburst occurrences in confined conditions including the exploitation of

remnants were identified. This study investigates geomechanical aspects of longwall mining in the areas

affected by old excavations aimed at relaxation of a multi-bed deposits within a thick coal seam or a group

of seams. It is assumed that high-energy seismicity is another factor determining the rockburst hazard

alongside the state of stress. A case study is recalled, describing a colliery where mining-induced seismic

activity of a de-stressed coal seam remained at the level comparable to or higher than it was experienced

in the de-stressed seam operations. An analytical model was used to study the stress state and potential

loss of structural continuity of an undisturbed rock body surrounding the longwall panel being mined

beneath or over the abandoned workings. Recalling the developed model of the system involving nonlinear

functions demonstrating the existence of abandoned mine workings within the rock strata, computer

simulations were performed to evaluate the rockburst hazards along the face area. Discussions of results

are based on observations of immediate roof convergence and the vertical stress concentration factor at

the longwall face zone. Computational data of the modelled mining situations demonstrates that despite

using the de-stressing method of mining, the occurrence of events impacting on mine working beneath

and over abandoned workings cannot be precluded. Here the scale of rockburst hazards is determined by

local mining and geological conditions, such as the type and extent of abandoned workings, their age and

vertical distance between them and the coal seam currently mined.

The underground mining of coal deposits in the Upper Silesian Coal Basin (GZW) re-sults in an imbalance in the distribution of the stress in the rock mass, both in the immediate and distant surroundings of mining excavations. The occurrence of seismic tremors, among others, is the consequence of this process,. The intensities of seismic phenomena, which occur in several regions of the GZW (Bytomian Basin, Main Saddle, Main Basin, Kazimierzowska Basin, and the Jejkowice Basin) are very diverse, ranging from tremors unrecognizable by humans to strong tremors of the nature of weak earthquakes (Patyńska and Stec 2017). During the period of 15 years, i.e. from 2001 to 2015, the level of seismic activity changed and de-pended on both the intensity of the excavation work and the variability of the lithological and tectonic structures. On the other hand, the seismic activity analysis has shown that in recent years, despite a decrease in total output, seismic activity and rockburst hazard have increased. One of the rea-sons was the increase in mining output. Almost half of the output came from coal seams under the rockburst hazard. This resulted in an increase in the number of great energy tremors with the energy of 107, 108 and 109 J. It has been shown that the amount of energy tremors has a high impact on the level of the rockburst hazard. Between 2001 and 2015, as many as 20 rockburst were caused by seismic tremors above 107 J with 42 total phenomena (Patyńska 2002–2016). The purpose of characterizing the causes of this phenomenon was determined by the parameters characterizing the structure of the rock mass in places where the rockburst was recorded.

Mining-induced seismicity, particularly high-energy seismic events, is a major factor giving rise to dynamic phenomena within the rock strata. Rockbursts and stress relief events produce the most serious consequences in underground mines, are most difficult to predict and tend to interact with other mining hazards, thus making control measures difficult to implement. In the context of steadily increasing mining depth within copper mines in the Legnica-Głogów Copper Belt Area (Poland) alongside the gradually decreasing effective mining thickness, a study of the causes and specificity of mining-induced seismicity in specific geological and mining settings may improve the effectiveness of the prevention and control measures taken to limit the negative impacts of rockbursts in underground mine workings, thus ensuring safe working conditions for miners. This study investigates the presumed relationship between the mined ore deposit thickness and fundamental parameters of mining-induced seismicity, with the main focus on the actual locations of their epicenters with respect to the working face in commonly used room-and-pillar systems. Data recalled in this study was supplied by the O/ZG Rudna geophysics station. Based on information about the actual ore deposit thickness in particular sections of the mines (Rudna Główna, Rudna Północna, Rudna Zachodnia) and recent reports on seismic activity in this area, three panels were selected for further studies (each in different mine region), where the ore deposit thickness was varied (panel G-7/5 – Rudna Główna, panel XX/1 – Rudna Północna, panel XIX/1 – Rudna Zachodnia). Data from seismic activity reports in those regions was used for energetic and quantitative analysis of seismic events in the context of the epicenter location with respect to the selected mining system components: undisturbed strata, working face and abandoned excavations. In consideration of the available rockburst control methods and preventive measures, all events (above 1 × 103 J) registered in the database were analysed to infer about the global rockburst hazard level in the panel and phenomena induced (provoked) by blasting were considered in order to evaluate the effectiveness of the implemented control measures.

For the prevention and control of rockburst in underground coal mines, a detailed assessment of a rockburst hazard area is crucial. In this study, the dependence between stress and elastic wave velocity of axially-loaded coal and rock samples was tested in a laboratory. The results show that P-wave velocity in coal and rock is positively related to axial stress and can be expressed by a power function. The relationship showed that high stress and a potential rockburst area in coal mines can be determined by the elastic wave velocity anomaly assessment with passive seismic velocity tomography. The principle and implementation procedure of passive seismic velocity tomography for elastic wave velocity were introduced, and the assessment model of rockburst hazard using elastic wave velocity anomaly was built. A case study of a deep longwall panel affected by rockbursts was introduced to demonstrate the effectiveness of tomography. The rockburst prediction results by passive velocity tomography closely match the dynamic phenomenon in the field, which indicates the feasibility of elastic wave velocity anomaly for rockburst hazard prediction in coal mines.