The influence of the geometrical construction of the powered roof support on the loss of a longwall working stability based on the practical experience

This article focuses on the difficulties in ensuring longwall stability resulting from the wrong geometric form of the structure of powered support sections. The authors proved, based on the in-situ measurements and numerical calculations, that proper cooperation of the support with the rock mass requires correct determination of the support point for the hydraulic legs along the length of the canopy (ratio), as well as the inclination of the shield support of the section of the powered roof support. The lack of these two fundamental elements may lead to roof drops that directly impact the production results and safety of the people working underground. Another matter arising from the incorrect geometric form of the construction are the values of forces created in the node connecting the canopy with the caving shield, which can make a major contribution to limit the practical range of the operational height of the powered roof support (due to interaction of powered support with rockmass) in terms of the operating range offered by the manufacturer of the powered support. The operating of the powered roof support in some height ranges may hinder, or even in certain cases prevent, the operator of powered support, moving the shields and placing them with the proper geometry (ensuring parallelism between the canopy and the floor bases of the section)

Optimisation of selected parameters of the shield support base dedicated for the condition of a weak floor

In longwall coal exploitation, problems with the proper functioning of the powered shield support often occur. In many cases, it results from the insufficient load-bearing capacity of the ground (floor) and the inability to achieve the set or yield pressure of the shield support. The improper functioning of the shield support may also result from its construction and the lack of optimisation to work effectively on a weak mine floor. This paper presents an attempt to optimise the operating conditions of the base of two-legged shield support based on the field observations and results of the PFC3D numerical calculation. In the framework of the numerical calculations, the impact of the width of the base and the location of the hydraulic legs on the working conditions of shield support on a weak floor were analysed

Model tests of the rock mass destroying mechanism due to hanging roof in a longwall working

W artykule zwrócono szczególną uwagę na zagadnienie związane z trudnością w utrzymaniu stateczności wyrobiska ścianowego w przypadku niekorzystnego zjawiska zawisania stropu wyrobiska ścianowego w warunkach prowadzonej eksploatacji systemem ścianowym na zawał. W tym celu przeprowadzono badania analityczne i numeryczne z zamiarem określenia parametrów, które determinują proces zawisania warstwy stropu wyrobiska ścianowego. Metodą analityczną badano wpływ parametrów fizyko- -mechanicznych oraz geometrycznych górotworu na proces zawisania stropu wyrobiska ścianowego nad zrobami interpretowany wartością jego ugięcia. Przedstawiono schemat obliczeniowy oraz warunki wytrzymałościowe procesu wydłużania belki (wspornika) w stropie wyrobiska. Natomiast za pośrednictwem obliczeń numerycznych badano wpływ wybranych parametrów modelu Coulomba-Mohra na wartości długości wspornika oraz obniżenia stropu dla określonych parametrów geometrycznych i mechanicznych obudowy zmechanizowanej. Otrzymane wyniki badań modelowych pozwoliły na określenie zależności opisujących wpływ wybranych parametrów mechanicznych skał i geometrycznych warstwy stropu wyrobiska ścianowego na proces jego powstawania i zawisania.The article focuses on the problem in maintaining the stability of a longwall working caused by the unfavourable phenomenon of the hanging roof in a longwall working. Model tests were carried out, intended to define the parameters that determine the process of roof hanging, based on the analytical and numerical methods. The analytical method was applied to study the influence of physic-mechanical and geometrical parameters of the rockmass on the process of roof hanging in the longwall working, interpreted the value of its deflection. The calculation scheme as well as the strength and stress conditions of the roof beam lengthening process in the longwall working are presented. Whereas, in the numerical calculations the influence of parameters of the Coulomb-Mohr’s model on the length and the deflection of the roof strata for given geometrical and mechanical parameters of the powered roof support, were investigated. The obtained results allowed to determine parameters describing influence of the selected mechanical and geometric parameters of the roof of the longwall working on the process of its hanging

Safety of longwall mining with caving in the light of data from monitoring system

Obudowy zmechanizowane zwykle postrzega się jako urządzenia składające się głównie z części mechanicznej i hydraulicznej, natomiast pozostałe wyposażenie, głównie związane z elektroniką, traktowana jest często jako konieczne uzupełnienie systemu, zapewniające możliwość jego sterowania. Jednak rozwinięcie funkcjonalności związanych ściśle z najnowszą elektroniczną częścią wyposażenia kompleksów wydobywczych, głównie o możliwości pomiarowe i rejestracyjne, pozwala również na coraz częstsze stosowanie różnego rodzaju monitoringu, umożliwiającego obserwację pracy kompleksu wydobywczego w czasie rzeczywistym lub z niewielkim opóźnieniem czasowym, także sygnalizację stanów zagrożeń lub nieprawidłowości. Najbardziej zaawansowane systemy wyposażane są w funkcje analizujące zmiany monitorowanych parametrów, dla wypracowania ostrzeżeń o możliwych przyszłych zagrożeniach, by z wystarczającym wyprzedzeniem czasowym umożliwić reakcję operatora. Stworzenie takiego systemu predykcji wymaga zgromadzenia, a następnie przeanalizowania odpowiednio dużej i kompletnej bazy pomiarów i obserwacji, związanych przede wszystkim z różnymi utrudnieniami w prowadzeniu obudowy zmechanizowanej, a szczególnie z wydarzeniami stricte awaryjnymi, takimi jak np. obwały, stany zaciśnięcia sekcji itp. Odpowiednio opracowane zależności i wyniki analiz mogą optymalizować bezpieczeństwo pracy załogi, ograniczać trudności w utrzymania stropu wyrobisk ścianowych i co za tym następuje pozytywnie wpłynąć na uzyskiwane wyniki ekonomiczne.Shield supports are usually perceived as devices consisting mainly of mechanical and hydraulic parts, while other apparatus, mainly related to electronics, is often treated as a necessary supplement to the system which ensures its control. However, the development of features closely related to the latest electronic equipment in the mining complexes, mainly connected with measuring and registration possibilities, also allows for more and more frequent use of various types of monitoring. It enables observation of the operation of the mining complex in real time or with a slight time delay. What is more, it also enables signalling the operating states of the shield constituting specific threats or irregularities. The most advanced systems found abroad are equipped with functions analysing changes in specific monitored parameters to develop warnings about possible future threats to allow the operator to react with sufficient time in advance. Developing such a forecast system requires gathering and then analysing a sufficiently large and complete database of measurements and observations. These are primarily associated with various difficulties in operating a shield support, and especially with strictly emergency states, such as rock slides, shield clamping conditions, etc. The data from monitoring of shield support operation, through proper development of dependencies and analysis results, can optimize the safety of crew, reduce difficulties in maintaining the roof of longwall excavations and thus have a positive impact on the obtained economic results

A Pen206 borehole jack suitability assessment for rock mass deformability determination

Currently available field rock mass deformability determination methods are rather difficult to perform, due to their complexity and a time-consuming nature. This article shows results of a suitability assessment of a Pen206 borehole jack (a hydraulic penetrometer) for field rock mass deformability measurements. This type of the borehole jack is widely used in Polish hard coal mining industry. It was originally intended only for quick rock mass strength parameters determination. This article describes an analysis and scope of basic modifications performed mainly on a borehole jack head. It includes discussion of results with possible directions for future development of the device

An investigation of longwall failure using 3D numerical modelling – A case study at a copper mine

It is well-known that the longwall mining method (with roof caving) is widely used in underground mining extraction for bedded deposits (e.g. coal) due to its numerous advantages. Generally, this method is not commonly applied for ore deposits such as copper deposit. In Poland, the longwall mining method has been tested for thin copper deposits at the Polkowice-Sieroszowice copper mine (KGHM). Various failure modes were observed during longwall operation in the 5A/1 panel. This paper aims to examine these occurred failures. To do so, an analysis has been conducted using 3D numerical modelling to investigate the failure mode and mechanism. Based on the 3D numerical modelling results with extensive in situ measurements, causes of failure are determined and practical recommendations for further copper longwall operations are presented

The role of powered support in ensuring the proper longwall working cross-section area in rockburst-prone seams

In Poland, for underground hard coal seam extraction, the longwall method is used. Retreat longwalls with natural roof caving in the gob are the most common. Currently it is estimated that about a half of the hard coal output in Poland originates from seams located in areas of rock burst hazard. The article shows information about 18 rock bursts, and 14 other seismic events which occurred between 2003 and 2012 in underground mines belonging to one of coal companies in Poland. In addition, negative consequences of those dynamic phenomena in the longwall workings are described. In the next part of paper, the most common types of damage to powered supports after the rock mass tremors and other dynamic phenomena in longwall workings are shown. In order to avoid damage of powered supports, in geo-mining conditions where dynamic phenomena occur, different types of protective means are applied. In the paper the methodology of assessing the powered support yield ability is described. At the end, an example of the assessed yield ability of a powered support in given geo-mining conditions of a longwall face affected by the seismic events is presented

Geomechanical assessments of longwall working stability – a case study

The stability of longwall mining is one of the most important and the most difficult aspects of underground coal mining. The loss of longwall stability can threaten lives, disrupt the continuity of the mining operations, and it requires significant materials and labour costs associated with replacing the damages. In fact, longwall mining stability is affected by many factors combined. Each case of longwall mining has its own unique and complex geological and mining conditions. Therefore, any case study of longwall stability requires an individual analysis. In Poland, longwall mining has been applied in underground coal mining for years. The stability of the longwall working is often examined using an empirical method. A regular longwall mining panel (F3) operation was designed and conducted at the Borynia-Zofiówka-Jastrzębie (BZJ) coal mine. During its advancement, roof failures were observed, causing a stoppage. This paper aims to identify and determine the mechanisms of these failures that occurred in the F3 longwall. A numerical model was performed using the finite difference method - code FLAC2D, representing the exact geological and mining conditions of the F3 longwall working. Major factors that influenced the stability of the F3 longwall were taken into account. Based on the obtained results from numerical analysis and the in-situ observations, the stability of the F3 longwall was discussed and evaluated. Consequently, recommended practical actions regarding roof control were put forward for continued operation in the F3 longwall panel

The role of powered support in ensuring the proper longwall working cross-section area in rockburst-prone seams

In Poland, for underground hard coal seam extraction, the longwall method is used. Retreat longwalls with natural roof caving in the gob are the most common. Currently it is estimated that about a half of the hard coal output in Poland originates from seams located in areas of rock burst hazard. The article shows information about 18 rock bursts, and 14 other seismic events which occurred between 2003 and 2012 in underground mines belonging to one of coal companies in Poland. In addition, negative consequences of those dynamic phenomena in the longwall workings are described. In the next part of paper, the most common types of damage to powered supports after the rock mass tremors and other dynamic phenomena in longwall workings are shown. In order to avoid damage of powered supports, in geo-mining conditions where dynamic phenomena occur, different types of protective means are applied. In the paper the methodology of assessing the powered support yield ability is described. At the end, an example of the assessed yield ability of a powered support in given geo-mining conditions of a longwall face affected by the seismic events is presented

Numerical Simulation of the Impact of Unmined Longwall Panel on the Working Stability of a Longwall Using UDEC 2D—A Case Study

The main goal of the paper is numerical simulation for investigation of damage causes in the working of a longwall located under the unmined longwall panel. The paper presents the results of model-based research on the stability of the roof of a longwall working in a zone subject to cave-in mining, taking into account the influence of mining conditions in the form of an unmined coal seam located 115 m above the exploited seam. It presents the geometry of the rock mass under study, the discretization area of the solution, and gives an overview of the assumptions used to build the numerical model. The authors discuss the results of numerical simulations of the influence of mining phenomena on the formation of roof falls in the longwall. Based on the results of numerical simulations, the process of identifying the size of roof falls in a longwall working (loss of stability) was carried out through their appropriate classification. The case presented and analyzed in this paper occurred in one of Poland’s coal mines