Chronostratigraphic and Depth Variability of Porosity and Strength of Hard Coals in the Upper Silesian Basin / Chronostratygraficzna I Głębokościowa Zmienność Porowatości I Wytrzymałości Węgli W Górnośląskim Zagłębiu Węglowym

Abstract

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.