Rock bolts have long been used in Poland, above all in the ore mining. Worldwide experience (Australia, Chile, Canada, South Africa, Sweden, and USA) provides evidence of rock bolt supports being used for loads under both static and dynamic conditions. There are new construction designs dedicated to the more extreme operating conditions, particularly in mining but also in tunneling. Appreciating the role and significance of the rock bolt support and its use in Polish conditions amounting to millions of units per year, this article describes a new laboratory test facility which enables rock bolt testing under static load conditions. Measuring equipment used as well as the possibilities of the test facility were characterized. Tests were conducted on expansion rock bolt supports installed inside a block simulating rock mass with compression strength of 80 MPa, which was loaded statically as determined by taking account of the load in order to maintain the desired axial tension, which was statically burdened in accordance with determined program load taking into consideration the maintenance of set axial tension strength at specified time intervals until capacity was exceeded. As an experiment the stress-strain characteristics of the rock bolt support were removed showing detailed dependence between its geometrical parameters as well as actual rock bolt deformation and its percentage share in total displacement and deformation resulting from the deformation of the bolt support elements (washer, thread). Two characteristic exchange parts with varying intensity of deformation /displacement per unit were highlighted with an increase in axial force static rock bolt supports installed in the rock mass.Keywords: rock bolt support, laboratory test bed, stress-strain characteristics Obudowa kotwowa jest już od dawna stosowana w Polsce, przede wszystkim w górnictwie rudnym. Światowe doświadczenia (Australia, Chile, Kanada, RPA, Szwecja,USA) świadczą o stosowaniu obudowy kotwowej zarówno w warunkach obciążeń o charakterze statycznym jak i dynamicznym. W podziemnych wyrobiskach górniczych wykonywanych na dużych głębokościach, szczególnie przy eksploatacji złóż rud miedzi w kopalniach LGOM, w których stosuje się samodzielną obudową kotwową istnieje niebezpieczeństwo nieprzewidzianego odpadania bloków skalnych do przestrzeni roboczej. Podstawowym zadaniem kotwienia wyrobisk górniczych jest zapewnienie ich stateczności, jako zasadniczy warunek

The study summarises the operating characteristics of the powered roof support (shield) used in an automated plough system. Investigated longwall support units were controlled automatically or by section engineers and positioned in the ‘saw tooth’ configuration with respect to the longwall face (automatic mode) or linear to the face. Shield pressure data have been analysed in order to identify the impacts of particular factors on the pressure increase profiles. The analysis was supported by the Statistica software to determine the statistical significance of isolated factors. Equations governing the leg pressure at the given time instant were derived and the roof stability factor ‘g’ was obtained accordingly, recalling the maximal admissible roof displacement method recommended by the Central Mining Institute (Poland). In the current mining practice, its values are used in monitoring of strata behaviour as indicators of shield–strata interactions, particularly in the context of roof control in longwall mining. It is vital that the method used should be adapted to the actual conditions under which the longwall is operated. In the absence of such adaptations, there will be major discrepancies in results. The conclusions section summarises the current research problems addressed at the Department of Underground Mining, in which the support pressure data in longwall operations are used. The first aspect involves the delineation of deformations of a longwall main gate about 100 m ahead of the face. The second issue addressed involves the risk assessment of roof rock caving or rock sliding in the tail gate. Another aspect involves the standardisation of local conditions to support the methodology of interpreting shield–strata interactions in the context of work safety. These methods are being currently verified in situ.

Pulling chains are one of the most critical components of a plough longwall system. Their failure is hard to predict and results in costly and lengthy downtimes. Measurements of the actual forces acting on a plough chain are needed as they can provide important information about the nature of their operation and contribute to preventing their wear and failure by supplementing data gathered by a plough control station. In this work, a strain gauge system for the measurement of the forces in a plough chain is designed, manufactured and tested under real conditions for the first time. Constructed using a cylindrical strain gauge and widely available electronic components, the finished sensor was calibrated on a testing machine and used to measure forces in a 42 × 137 plough chain at LW Bogdanka. Measurements conducted under real conditions show that forces in the chain during steady ploughing does not exceed 400 kN. However, the forces peaked to up to 728.6 kN at certain points in the operation. The implications of such events are discussed. The device allowed for successful measurements of forces in difficult conditions of a mining plough longwall and provides new information on their course and characteristics, which is very valuable for plough operators and chain-life predictions. This work suggests the further integration of force sensors into longwall plough system.

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The emergence of the new SARS-CoV-2 virus two years ago strongly affected economic life and labour markets around the world. The pandemic affected many sectors, including the mining industry. Coal companies have had to cope with the challenges and adapt their operations to the situation. Due to the peculiarities of the mines, not only to the hazardous factors and conditions prevailing underground but also to the large number of employees who usually move in groups in the plants, the emergence of a new threat caused by a biological agent posed a real challenge for them. The aim of this paper was to present the initiatives and measures taken in the coal mining sector to ensure the safety of workers during a pandemic. The guidelines for the operation of mining plants during the SARS-CoV-2 epidemic were analysed, as well as the identification of locations in mining plants particularly vulnerable to infection with the virus. We also presented how the pandemic period affected the operations of a selected coal company in Poland from an economic point of view.