Investigations on Fracture Evolution of Coal Measure Sandstones from Mineralogical and Textural Points of View
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ORIGINAL PAPER
Investigations on Fracture Evolution of Coal Measure Sandstones from Mineralogical and Textural Points of View Ekin Ko¨ken1
Received: 21 December 2019 / Accepted: 25 March 2020 Indian Geotechnical Society 2020
Abstract The purpose of the present study is to investigate the variations in fracture evolution of sandstones arising from mineralogical and textural features. For this purpose, eight types of coal measure sandstones located in the Zonguldak Hardcoal Basin (ZHB) were considered. The mineralogical and textural characterizations of the rocks were carried out. Physico-mechanical properties were determined for each rock type. Based on quantitative strainbased methods, the crack initiation (rci) and crack damage (rcd) thresholds of the sandstones were determined. The laboratory test results indicate that the rci and rcd of the sandstones were found to be between 0.27–0.43 and 0.61–0.83 of the UCS, respectively. In general, the rci and rcd correspond to 0.37 and 0.71 of the UCS, respectively. The rci and rcd decrease with increasing the sorting coefficient (Sc), average grain size (d50, mm), contents of feldspar (F, %), and lithic fragment (LF, %). On the other hand, increasing quartz content (Qtz, %) increases those variables. Remarkable changes were obtained in the rci and rcd when effective porosity (ne) and pulse wave velocity (Vp) of the rocks exceed 3% and 3.00 km/s, respectively. As a result of mineralogical analyses and laboratory studies, statistical analyses were carried out. Accordingly, the rci and rcd could be estimated reliably using several empirical relationships established in the present study. In order to represent the importance and utilization of rock mineralogy and texture for underground mining applications in the ZHB, several suggestions and considerations related to a V-cut gallery blasting operation were introduced. & Ekin Ko¨ken [email protected] 1
Department of Materials Science and Nanotechnology Engineering, Abdullah Gu¨l University, 38100 Kayseri, Turkey
Keywords Sandstone Fracture evolution Crack initiation Crack damage Mineralogical and textural analyses
Introduction The mechanical behavior of rocks is of great importance to such investigations regarding open-pit and underground mining applications, tunneling, and extraction of natural resources such as coal, petroleum, natural gas, and hydrocarbons. In this respect, the fracture evolution of rocks stemming from drilling–blasting, excavation methods, and in situ stress states takes an important part in assessing the stability, reliability, and sustainability of those applications. Attempts to understand fracture mechanism around a rock mass have mainly involved laboratory investigations of rock materials, physical models as well as numerical analyses. On a theoretical basis, fracture evolution of rock materials under axial loading conditions is typically divided into four stages. These are crack initiation (1), crack propagation (2), unstable crack growth (3), and failure (4), each of which occurs
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