Influence of orthoclase phenocrysts on point load strength of granitic rocks

The point load index test involves loading cylindrical, block or irregular rock samples between two conical platens until sample failure. The point load strength index (Is) determined using failure load and sample dimension is widely and variously used in engineering geological studies. Therefore, a comprehensive knowledge about the factors that could influence the index value is necessary. This paper explores the effects of orthoclase phenocryst dimension on the point load strength index (Is) of granitic materials from Turkey. In this context, point load strength values of 117 granite core samples were determined. The granites used in this study included orthoclase phenocrysts as important mineral constituents. High-resolution image was obtained from the freshly fractured surface of each sample. The ratio of orthoclase phenocrysts (ROP) on the failure surface was determined using image analysis. When point load strength values were correlated with the ratios of orthoclase phenocrysts, an inverse relationship emerged. Issues in order to minimize the influence of orthoclase phenocrysts on the point load strength were discussed. ► There is an inverse relationship between ROP and point load strength value. ► Reduction in point load strength values are observed depending on the increase of ROP. ► Cleavage planes compose the weak zones of the minerals.