The article presents the results of tests of porosity of the Upper-Silesian Coal Basin (USCB) hard coals. The porosity was determined for various lithotypes of hard coal, collected in different areas of the Upper-Silesian Coal Basin. Samples of hard coal were collected in 60 seams of 16 coal mines, from the depth of approximately between 350 and 1200 m. There are also presented differences in values of open porosity of coal depending on the depth of occurrence, as well as chronostratigraphic and tectonic correlation of a seam. Uniaxial compression strength of the tested coals falls in the strength class from very low to very high (from 8.1 to 51.5 MPa), open porosity is 0.68–12.5% and total porosity is 3.29–17.45%. With an increase in depth, in general, open porosity of coals decreases. There is an apparent decrease in open porosity correlated with the age of hard coals. It was observed that the lower and upper limits of open porosity ranges of variability shift towards lower values the older the coals are, from the Łaziskie Beds to the Jaklowieckie Beds. The older the coals the greater the average drop in the share of open porosity in total porosity from 60% for the youngest coals to merely several per cent for the oldest ones. The highest values of total porosity (over 10%) were observed in the youngest coals (Cracow sandstone series and siltstone series). Older coals reached more diversified values of total porosity (3.29–17.45%). Based on the conducted tests, zones correlated with tectonics of the basin and with deposition of lithostratigraphic beds of specific age, where values of porosity of hard coals differ, were determined in the area of the USCB. However, in spite of their correlation to a structural unit, the coals demonstrated a decrease in open porosity with an increase in their geologic age. Thus, there is an apparent influence of the deposition depth of coal within a given structural unit on open porosity following the age of coal, i.e. correlation to an older and older chronostratigraphic unit. Porosity tests of hard coal are published in scientific journals yet, most often, there is no information on the type of porosity. Such detailed characteristics of open porosity for coal of the Upper Silesian Coal Basin, as in the article, have not been prepared yet, making our research novel. Such broad tests of porosity of hard coals, correlated with their strength and referring to the deposition depth of seams as well as a correlation to lithostratigraphic units within individual structural units in the USCB, had not been conducted yet. We believe it is a sufficient argument to start detailed research into the open porosity of hard coals. The results of the tests are important from both the research and practical points of view. Knowledge of coal porosity is indispensable in solving many engineering problems of geological engineering, mining geomechanics and mining e.g.: assessing behaviour of coal when it is mined and processed, assessing the possibility of capturing methane, which makes up over 90% of natural gas, from coal in the areas of methane-rich deposits; the possibility of storing various substances in abandoned hard coal mining areas (e.g. CO2 storage within the structure of coal), assessing risk of occurrence of certain natural hazards resulting from mining deposits (e.g. coal and rocks outburst hazard), as well as assessing the possibility of applying unconventional methods of mining hard coal deposits (e.g. underground coal gasification).
In the article, values of porosity and compression strength of hard coals from the area of the Upper Silesian Coal Basin are presented. Change of the stage of carbonification, which results from conversion of coal substance in the process of coalification, is a source of many changes in the structure of coal. These changes exert influence on values of physical parameters, including value of porosity and strength. Porosity and compression strength change with the degree of carbonification which is a result of the depth of deposition. Presented in the article, values of effective porosity of coals and their strength have been determined considering age chronology of coal seams and depth of their occurrence. Coals of the Cracow Sandstone Series, the Mudstone Series, the Upper Silesian Sandstone Series and the Paralic Series, from depth ranging from about 350 m to about 1200 m, were examined. The authors have shown that effective porosity of the Upper Silesian coals changes for particular stratigraphic groups and assumes values from a few to a dozen or so per cent, while compression strength from several to several dozen megapascals. It has been observed, from chronostratigraphic perspective, there is a shifting of the upper and lower limit of intervals of porosity variations towards higher values for younger coals. With the increase of compression strength, value of porosity in particular stratigraphic groups generally decreases. However, no regular changes were observed of mean uniaxial compressive strength with the increase of age of subsequent stratigraphic groups. On the other hand, for bright coal and semi-bright coal, visible decrease of compression strength with the depth of deposition of strata was observed.
In this work a method, developed by the author, of microscopic investigations of deformation structures occurring in rock medium is presented. This method is based on adoption of multi-stage complex procedure encompassing numerous diverse examinations and measurements. As a result of following this method, information about geometrical features of microfractures and microfissures distribution (coordinates, length, occurrence frequency and directions of propagation) is obtained, which in turn allow to determine the range and intensity of destruction zones around macroscopic fissures in investigated samples. Testing was performed on selected three samples of the Tumlin Sandstone (three microscopic sections), representing the following states of stress-strain: sample no. 1 (σ 3 = 200 MPa confining pressure and ε 1 = 5% longitudinal strain) sample no. 2 (σ 3 = 300 MPa confining pressure and ε 1 = 10% longitudinal strain) sample no. 3 (σ 3 = 300 MPa confining pressure and ε 1 = 15% longitudinal strain)On the basis of conducted research it has been stated that increasing confining pressure σ 3 = σ 2 results in the increase of number and range of microfissures occurrence. At confining pressure σ 3 = σ 2 200 MPa and longitudinal strain ε 1 = 5% a zone of intensive fracturing is noticeable, reaching about 6mm from the surface of macroscopic fracture. However, at higher confining pressure and higher longitudinal strains (σ 3 = σ 2 300 MPa and ε 1 = 10% as well as σ 3 = σ 2 300 MPa and ε 1 = 15%) microcracks and microfissures cover almost whole volume of the sample.Keywords: confining pressure, rock mass, slip surface, microcracks, stress, strain W artykule przedstawiono opracowaną przez autora metodę badań mikroskopowych struktur deformacji występujących w ośrodku skalnym. Metoda ta polega na zastosowaniu wieloetapowej złożonej procedury obejmującej wiele różnorodnych badań i pomiarów. W wyniku jej przeprowadzenia uzyskuje się informacje o geometrycznych cechach rozkładu mikrospękań i mikroszczelin (współrzędne, długość, częstość występowania i kierunki rozprzestrzenienia), które z kolei pozwalają na określenie zasięgu i intensywności strefy zniszczenia wokół pęknięć makroskopowych w badanych próbkach. Do badań zastosowano grubo ławicowy dolno triasowy piaskowiec pochodzący z północnej części obrzeżenia Gór
Abstract-Tests aimed to verify whether there is a correlation between the basic parameters characterizing the mechanical properties of rocks with the properties of ionizing radiation scattered by rocks were performed as part of the research. The positive correlation between the two examined properties would provide the basis for the development of a new method of rock testing using radiation sources or devices generating ionizing radiation. The method could be applied to carry out research in underground boreholes to determine the mechanical properties of the rock mass in situ. The study allowed the verification of the adopted assumptions for the proposed method. The verification was based on the correlation analysis of absorption coefficients of the ionizing radiation of rocks from the Upper Silesian Coal Basin with the results of the research on mechanical and physical properties.
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