Determination of stress state in rock mass using strain gauge probes CCBO

The strain gauge probes of different construction are typically used for determination of stress state rock mass. The modified overcoring method known as the Compact Conical ended Borehole Overcoring method (CCBO) for stress state determination in rock mass was designed in Institute of Geonics of the CAS (IGN) in cooperation with Kumamoto University in Japan. The implemented adjustment of the overcoring method consists mainly in omitting the overcoring phase (stress relief phase). The probe is glued directly to the conically shaped end of a borehole. The data logger located within the conical probe enables continual strain monitoring directly in the conically shaped end of the borehohole during the overcoring procedure. The conical probe used to monitor stress changes, named Compact Conical ended Borehole Monitoring (CCBM), can continuously monitor rock strain changes in key locations due to mining. Many stress measurements using both strain gauge probes CCBO and CCBM were carried out in the last decade. These measurements were performed in varied rock mass adjacent to mine excavations. Most of the stress measurements were carried out in Carboniferous sedimentary rocks as part of the experimental work in the Czech part of the Upper Silesian Coal Basin (USCB). Several stress measurements were carried out during the mine development operations and associated geotechnical exploration work while constructing the Milasín - Bukov underground gas storage (BUGS) [1], as well as the Bukov Underground Research Laboratory (BURL) [2]. Both underground facilities were designed within Rožná and Olší uranium deposits situated on the north-eastern margins of the Strážek Unit consisting of the metamorphic rock formations. Several measurements were carried out in granitic environments (igneous rocks) as part of the international Large-Scale Monitoring (LASMO) project in Grimsel (Switzerland) and in Josef underground laboratory (Bohemian massif). The article presents the basic principles and the methodology of stress measurements in rock mass using strain gauge probes and the data analysis from the variable rock environments

Topographic inspection as a method of weld joint diagnostic

U radu se demonstrira topografsko ispitivanje u specifičnom kontekstu triju vrsta inspekcijskih metoda zavara od austenitnog nehrđajučeg željeza. Vizualna i metrološka kontrola provedena je tijekom ispitivanja zavarivanja TIG postupkom, primjenom ne-destruktivnih metoda: rendgensko ispitivanje, kompjuterizirana tomografija i profilometrija površine. Rad je reakcija na nedostatak informacija, posebice u području ne-destruktivnih metoda prikladnih za široku primjenu u praksi. U radu se prezentiraju prednosti i nedostaci analiziranih dijagnostičkih metoda i klasifikacija uobičajenih i specifičnih mana zavarenog spoja. Najvažnija neispravnost u praktičnim primjenama kod određivanja pouzdanosti zavarenog spoja su pukotine. Ova vrsta dijagnoze zasnovana je na dobivenim podacima o promatranom anizotropskom i nehomogenom volumenu u dijelu zavara pod utjecajem topline.The paper demonstrates a topographic inspection in the specific context of three kinds of inspection methods of austenitic stainless steel welds. Visual and metrological inspection was analysed during tungsten inert gas (TIG) welding tests, showing the non-destructive techniques: X-ray, computed tomography, and surface profilometry. The article is a response to the lack of information, especially in the area of non-destructive techniques suitable for wide practical application. The Paper presents advantages and drawbacks of the analysed diagnostic methods and a classification of conventional and specific welded joint flaws. The most important defect in practical applications determining reliability of a welded joint is cracks. This kind of diagnostic is based on the obtained information about anisotropic and inhomogeneous volume under consideration in the heat-affected zone of a weld

Experimental approach to measure stress and stress changes in rock ahead of longwall mining faces in Czech coal mines

The measurement and monitoring of stress in rock mass are very important tasks in mining geomechanics. With increasing mining depth and worsening of the geological and mining conditions, a suitable method to determine and monitor rock stress and stress changes due to longwall coal mining is needed. Detailed knowledge of the stress state in rock mass is very useful when designing safe mining activity, especially in rockburst areas. The paper presents a brief description of the Compact Conical-ended Borehole Monitoring (CCBM) method for rock stress evaluation and the technical details of this innovative technology. The second part of the contribution evaluates and discusses initial results and experience obtained from the use of CCBM equipment for determination and observation of mining-induced stresses during mining of selected longwall panels in the conditions of the deep coal mines of the Upper Silesian Coal Basin

Stress Measurement in Coal Seam Ahead of Longwall Face – Case Study

Stress measurement and stress monitoring is an important task in mining geomechanics, because knowledge of the stress-strain state in a rock mass is the determining factor for the proper planning of roadway support and for the correct design of underground mining. This strategy is useful for ensuring mining safety, because increasing depth causes several issues, especially in areas with rockburst hazard, when roadways are loaded by the pressure ahead of an advanced longwall or by the stresses induced by destress blasting in overlying rock. Besides, mining is influenced by stress induced by previous excavations, mining edges in the overburden or abandoned workings in the same seam. The paper presents experiments with Compact Conical-endedBorehole Monitoring (CCBM) probes, which were used for stress monitoring in the area of a high-capacity coal face at Karvina Mine at the Lazy site (Czech Republic). This longwall panel is influenced by all the factors mentioned above. Monitoring of stress changes was carried out by using conical probes (CCBM) glued into a special cement body, which was installed directly into the coal seam. The basic description of the probe installed in the coal, the method of installation and the measurement results are the subject of this contribution. Another aim of the paper is to compare the measured values with the theoretical assumptions and mathematical model results

Stress state monitoring in the surroundings of the roadway ahead of longwall mining

Accurate knowledge of the stress-strain state of rock mass, not only in their vicinity but also in the wide surroundings of mine workings, is absolutely critical for precise support designing. Investigation of the rock stress is usually carried out by interpretation of the rock mass deformation processes, which can be relatively precisely observed and measured. In order to verify the stress state of the rock mass and changes in it induced by longwall mining, monitoring of changes in the rock mass stress in connection with the mine out of the longwall No. 371 202 was carried out. The seam extracted by monitored longwall has a thickness of approximately 2 m at a depth about 1100 m and lies within the Czech part of the Upper Silesian Coal Basin. Interpretation of the initial rock mass stress tensor and verification of its changes during longwall mining were the aims of this stress monitoring. A total of five probes were installed on the roof rocks of the main gate. Two compact conical-ended borehole overcoring probes were installed to obtain the pre-mining full stress tensor and afterwards three compact conical-ended borehole monitoring probes were installed to continuously monitor the stress state in the rock mass ahead of the advancing longwall. The monitored stress development contributes to our knowledge of stress distribution and its changes during excavation at great depth in multi-seam sedimentary deposits of the Upper Silesian Coal Basin