Investigations of P-Wave velocity, mechanical behavior and thermal properties of anisotropic slate

Abstract

Rock anisotropies are an important indicator for design and construction of various engineering projects across the world. To investigate the anisotropic characteristics of P-wave velocity, mechanical behavior and thermal properties, laboratory tests were performed on slate samples with various foliation orientations with respect to horizontal direction. The results indicate that the uniaxial compression strength (UCS) exhibits a typical U-type trend, the Young's modulus first decreases and then increases, and the variation of Poisson's ratio shows an opposite trend with the variation in Young's modulus. The anisotropy in strength is greater than that in deformation. Three typical failure modes, i.e. splitting across the foliation planes, shearing and sliding along the foliation planes, and axial splitting failure along the foliation planes, were observed. Scanning electron microscope (SEM) was also applied to analyze the microscopic failure mechanisms. It shows that the slate anisotropies are intrinsically attributed to the directional arrangement of mineral compositions observed by polarizing microscope. P-wave velocity and thermal conductivity both increase with increasing foliation angle, but the linear coefficients of thermal expansion show a decreasing trend. A new empirical formula was then proposed for describing the P-wave velocity and thermal parameters with respect to foliation angle of slate. It displays the empirical predictions match the laboratory measurements. The obtained results can better facilitate our understanding of mechanical behavior and thermal properties of anisotropic rocks, which should be considered in underground engineering applications in layered strata.