Effect of petrographic characteristics on physico-mechanical properties of Granitic gneisses from Islampur and Shir Atraf areas, Swat, NW Pakistan.

Abstract

To determine the effect of petrographic characteristic on physico-mechanical properties of Swat granitic gneisses field studies combined with petrographic and physico-mechanical investigations were conducted. The field observations indicate that the studied rocks are granitic gneisses. Based on the field and petrographic characteristics the exposed granitic rocks in both areas i.e., Shir Atraf and Islampur granitic gneisses were divided into different varieties. The Shir Atraf granitic gneisses were divided to two different varieties such as Shir Atraf medium grained variety and Shir Atraf coarse grained variety. The Islampur granitic gneisses were divided in to three different varieties Islampur fine grained variety, Islampur medium grained variety and Islampur coarse grained variety. Petrographic study reveals that the essential minerals found in all varieties are quartz, alkali feldspar and plagioclase. Biotite, muscovite, epidote, chlorite, garnet, tourmaline, and ore minerals are also present in minor to accessory amount. To determine the physico-mechanical properties Uniaxial Compressive Strength (UCS), Uniaxial Tensile Strength (UTS), specific gravity, water absorption, and porosity were performed. Different graphs have drawn to show the possible relationship between petrographic characteristics and physico-mechanical properties. In conclusion, based on above studies (i.e., petrographic studies and physico-mechanical properties) reveal that the mineralogical composition, grain shape, grain size, density, grainsize distribution, micro-fractures, grain contact types, degree of weathering, cleavage planes, all have an impact on mechanical properties. According to IAEG (International Association of Engineering Geologists) standards, the analysed rocks' UCS values are strong, whereas ISRM (International Society of Rock Mechanics) standards place them in the moderate to high strength category. The UCS and UTS values, as well as porosity, water absorption, and specific gravity, are all within acceptable limits for usage as construction material in heavy projects such as highways, buildings, tunnels, dams, and railway tracks.