Investigations on Fracture Evolution of Coal Measure Sandstones from Mineralogical and Textural Points of View

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 strain-based methods, the crack initiation (σci) and crack damage (σcd) thresholds of the sandstones were determined. The laboratory test results indicate that the σci and σcd of the sandstones were found to be between 0.27–0.43 and 0.61–0.83 of the UCS, respectively. In general, the σci and σcd correspond to 0.37 and 0.71 of the UCS, respectively. The σci and σcd 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 σci and σcd 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 σci and σcd 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.