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1

Predictive model of seismic vibrations’ peak value induced by multi-face blasting

Fuławka Krzysztof, Stolecki Lech, Mertuszka Piotr, Szumny Marcin, Anderko Arkadiusz

Journal of Sustainable Mining

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2023

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Vol. 22. iss. 3

248--256

EN

The seismicity level induced by blasting in the Polish copper mines is very important inlight of the efficiency of active rockburst prevention and safe conduct of blasting operations in the vicinity of the mining infrastructure such as shafts, workings, or function chambers (e.g., workshops, storages, etc.). Knowledge of the seismic vibrations' peak value might be the basis for designing blasting works in a way that ensures desired seismic effect. However, current experiences show that Peak Particle Velocity prediction models developed so far do not apply to multi-face blasting, where there are many vibrations’ sources at the same time dotted across the mining panel. This paper presents the assumptions of a new empirical model with validation data gathered in the underground trials of group blasting. This new method allows for determining the vibration level generated by firing a single face and the value of amplitude amplification resulting from the increased number of faces fired simultaneously in the group. Preliminary analysis shows that this newly developed predictive model is characterized by a high level of reliability and therefore was applied to assess the effectiveness of blasting works in the selected panel in one of the mines belonging to KGHM Polska Miedz S.A.

2

Panel destressing strategies for remnant pillar extraction

Vennes Isaac, Mitri Hani

Journal of Sustainable Mining

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2022

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Vol. 21, iss. 3

228--240

EN

Large-scale panel destressing is a rockburst mitigation technique employed in deep hard rock mines during remnant pillar extraction. Panels are choke blasted in the pillar footwall to cutoff the far-field major stress in the mining area and deviate them around the pillar. In this study, the effects of panel geometry and far-field stress magnitude are investigated. Destress blast performance is assessed by measuring change to the energy release rate (ERR) of all mining steps during the extraction of a simplified remnant pillar due to destressing. It is demonstrated that the energy release rate (ERR) of critical stopes is reduced by 30% with the base panel geometry. The panel thickness is shown to have the most influence on the efficiency of destressing, followed by the stand-off distance between the panel and the pillar and the overhang length of the panel. The effect of far-field stress magnitude on the ERR is also investigated, and the destress blast performance is expressed as an equivalent major principal stress reduction. It is shown that with the base panel geometry, the destressing program offers the same ERR reduction as a 9.6 MPa reduction in the far-field stress for the most critical stopes. Finally, the Copper Cliff Mine (CCM) panel destressing program is presented as a case study. The ore at risk and ERR are calculated over the extraction and destressing sequence in the pillar with a pillar-wide numerical model.

3

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

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

Journal of Sustainable Mining

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2022

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Vol. 21, iss. 4

278--297

EN

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.

4

Novel approach for the destress blasting in hard rock underground copper mines

Mertuszka Piotr, Szumny Marcin, Fuławka Krzysztof, Kondoł Piotr

Journal of Sustainable Mining

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2022

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Vol. 21, iss. 2

141--154

EN

The present study investigates the possibility of developing a novel method for reducing seismicity and rockbursts in deep underground mines based on modifying drilling and blasting patterns. The main goal was to develop and implement firing patterns for multi-face production blasting, which allow increasing the capability of inducing stress relief in the rock mass, manifested in the seismic event. This method may improve stability control in underground workings, and mitigate risks associated with the dynamic effects of rock mass pressure compared with currently used methods. Thus, the seismic energy may be released immediately after blasting in a controlled way. For this purpose, underground tests using modified blasting patterns and precise electronic detonators were carried out. Vibration data recorded from the multi-face blasting in the considered trial panels were assessed in the scope of amplitude distribution. Results of trials have proven that the method is promising and should be further developed to improve the effectiveness of rockburst prevention in deep hard rock mines.

5

Estimation of active rockburst prevention effectiveness during longwall mining under disadvantageous geological and mining conditions

Wojtecki Ł., Konicek P.

Journal of Sustainable Mining

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2016

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Vol. 15, iss. 1

1--7

EN

Underground longwall mining of coal seams in the Upper Silesian Coal Basin is currently being carried out under increasingly difficult geological and mining conditions. Mining depth, dislocations and mining remnants are the main factors responsible for the most significant rockburst hazard, which can be minimized via the use of active and passive rockburst prevention. Active rockburst prevention in longwalls is usually based on blasting, in order to either destress local stress concentrations in the rock mass or to fracture the thick layers of strong roof rocks to prevent or minimize the impact of high energy tremors on excavations. The accurate estimation of active rockburst prevention effectiveness is particularly important when mining under disadvantageous geological and mining conditions, which are associated with high levels of this hazard. The efficiency of blasting applied for this purpose is typically evaluated from the seismic effect, which is calculated based on seismic monitoring data and the weight of the charged explosive. This method, as used previously in the Czech Republic, was adopted in the present study to analyze conditions occurring in a Polish hard coal mine in the Upper Silesian Coal Basin. Parameters of long hole destress blastings in roof rocks (torpedo blastings) from the face of the assigned longwall in coal seam no. 507 were correct a success according to the seismic effect method and corresponded to observations made in situ. The analytical method presented enables the rapid estimation of destress blasting effectiveness and could also be useful when determining appropriate active rockburst prevention.

6

Sposób zmniejszania ryzyka sejsmicznego w kopalniach KGHM Polska Miedź S.A. metodą monitorowania deformacji otworów wiertniczych

Orzepowski S., Butra J.

Rudy i Metale Nieżelazne

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2011

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R. 56, nr 2

59-63

PL

W celu monitorowania "bezpiecznej" transformacji skały w filarze górniczym ze stanu sprężystego do stanu pokrytycznego, powodowanej postępem frontu wydobywczego, opracowano czujnik deformacji otworu wiertniczego typu DL (Diameter- Length). Czujnik instalowany w centralnym obszarze filara mierzy wartość D - zmianę średnicy poziomego otworu w kierunku pionowym oraz L - deformację skały otaczającej otwór mierzoną w kierunku osi otworu (obie mierzone z rozdzielczością pomiarową nie gorszą od 2 mikrometrów). Specyficzna relacja pomiędzy mierzonymi wartościami D i L w czasie procesu eksploatacji złoża, potwierdza "bezpieczną" transformację skały jądra filaru do stanu pokrytycznego, albo wskazuje, że jądro filara znajduje się nadal w stanie sprężystym. W takich przypadkach konieczne są aktywne działania profilaktyczne, np. zastosowanie strzelania odprężającego dla uniknięcia tąpnięcia filara.

EN

In order to monitor a "safe" transformation of mine pillar core from elastic to the post-critical state caused by the advancing mining faces, sensor for borehole deformation measurement of DL (Diameter-Length) type was developed. The sensor, installed in the central area of the pillar, measures the D - vertical diameter deformation of the horizontal borehole and L - deformation of the rock-mass along the axis of borehole (both with definition better than 2 micrometers). Specific relationship between D and L values, measured during the mining face progress, confirms "safe" transformation of the pillar core into the post?critical state or indicates an "unsafe" one, which means that pillar remains in the dangerous elastic state. In this case, relaxing blasts are necessary to avoid the risk of pillar type bump.