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3 Journal of Sustainable Mining

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European feedback on post-mining seismicity

Contrucci Isabelle, Namjesnik Dalija, Niemz Peter, Primo Paloma, Kotyrba Andrzej, Mutke Grzegorz, Konicek Petr, Dominique Pascal, Rudolph Tobias, Möllerherm Stefan, Kinscher Jannes, Klein Emmanuelle, Cesca Simone

Journal of Sustainable Mining

2023

Vol. 22. iss. 3

195--218

Following the Paris Agreement adopted in 2015, Europe has committed to reducing its greenhouse gas emissions. In this context, the abandonment of coal as an energy source, both in terms of consumption and production, will lead to the closure of many mines in the years to come. Mine closure guidelines to manage residual mining risks already exist in European countries. However, they do not include post-mining seismic risk management due to a lack of sufﬁcient studies and knowledge on this subject. After mining closure, the ﬂooding of the mining works leads to hydromechanical loading of the underground and, in the longer term, to diffusion and an increase in the pore pressure. These conditions can lead, in certain situations, to the reactivation of tectonic faults, which may cause seismic events strong enough to be felt on the surface or even produce damage. Events of lower magnitudes, usually attributed to the remobilization of old mining works, are referred to as post-mining seismic hazards. The European RFCS PostMinQuake project, which started in 2020, aims to study this hazard at ﬁve mining basins located in France, Germany, Poland and the Czech Republic, known to have experienced signiﬁcant seismicity during their operation. This analysis, based on the feedback of the partners of the project, aims to frame an inventory of the ﬁve studied mining basins, which all encounter post-mining seismicity problem today. Three basins out of ﬁve show events with local magnitudes of the order of 3-3.5, which took place between nine and thirteen years after the closure of the mines. Even though the magnitudes of these earthquakes are small to moderate, they are felt on the surface as they occur at shallow depths. In all of the considered countries, a national seismological network exists, however, none of them is fully dedicated to post-mining seismic monitoring. These networks generally consist of a sparse mesh of stations, which does not allow the detection of events of magnitude less than 1 and the location of events have high spatial uncertainties. France is not an exception, but it relies on microseismic monitoring to detect early signs of instability at the level of mining structures and to anticipate the possible appearance of surface disorders. Out of the ﬁve basins that are studied, the Gardanne basin, which has been monitored since 2008, is the most documented case study of post-mining seismicity. This article also shows the difﬁculty in identifying the key conditions and factors that can lead to the remobilization of faults.

Seismic activity and flooding of hard coal mines in the Ostrava-Karvina Coalfield

Konicek Petr, Jirankova Eva, Kajzar Vlastimil, Schreiber Jan, Malucha Pavel, Schuchova Kristyna

Journal of Sustainable Mining

2022

Vol. 21, iss. 4

249--260

The termination of mining activities often results in post-mining problems and risks. One of these issues is the flooding of mines. Long-term mining in the Ostrava and Petrvald sub-basins in the Upper Silesian Coal Basin finished in 1994. Tens of coal seams were mined here, and the depth of mining reached more than 1000 m below the surface. Flooding of the Ostrava sub-basin started in 1994. The Ostrava and Petrvald sub-basins were flooded from one half only to prevent water from flooding into the Karvina sub-basin, where mining continued. The continual pumping of water has been carried out ever since. Only low-energy seismic events (up to 103 J) were recorded during the periods of flooding and water pumping. Only one high-energy seismic event was recorded here (108 J, magnitude of 3.5, 12 December 2017). This study presents the natural and mining conditions regarding the process of mine flooding; and the induced seismicity registered during the flooding of mines and the preservation of water at the stated level. Analysis of the flooding of mines in connection to the registered seismicity is presented. Probable reasons for the low seismic activity during the flooding of mines are also discussed.

Numerical modelling of destress blasting – a state-of-the-art review

Miao Shuting, Konicek Petr, Pan Peng-Zhi, Mitri Hani

Journal of Sustainable Mining

2022

Vol. 21, iss. 4

278--297

As a proactive mine safety measure against the occurrence of rockburst, destress blasting has been applied to numerous mining conditions to precondition highly stressed rock mass to mitigate the risk of rockburst occurrence in deep mines as well as in deep underground constructions. However, the application of destress blasting mostly depends on engineering experience, while its mechanism and efficiency have not been well understood. Rapid advances in computer technology have made numerical simulation an economical and effective method to study the rock blasting effect. Enormous research efforts have been made to numerically investigate the blasting fracture mechanism, optimize blasting design, and assess the efﬁciency of destress blasting. This review focuses on the state-of-the-art progress in numerical modelling associated with destress blasting over the last two decades. Some commonly used modelling approaches for destressing blasting are compared and reviewed. Currently, two different ways of modelling based on static and dynamic modes are typically used to study the effect of blasting. In the static method, destress blasting is simulated by modifying the rock mass’s stiffness and strength properties to obtain the post-blast stress state in the destressed zone. The dynamic modelling technique focuses on the dynamic fracture process of coals and rock masses, during which the predetermination of the damage induced by blasting is not necessary. Moreover, the extent of damage zones around the blast hole can be precisely estimated in the dynamic modelling method by considering time-varying blast pressure and strain rate dependency on the strength of rock mass but at the cost of increased computation and complexity. Besides, different destress blasting modelling methods, generally classified into continuum-based, discrete-based, and coupled methods, are compared and reviewed. The fracture mechanism of blasting in the rock mass is revealed, and the destressing efficiency of the existing destress blasting design is assessed and compared with classical results. The factors that may affect the efficiency of destress blasting are summarized. Finally, the difficulties and challenges associated with the numerical modelling of destress blasting are highlighted briefly.