Ultrasonic P-wave velocities in granite cores with an inclined joint filled with sand and clay under varying water contents

Natural rock masses exhibit diverse physical properties due to their formation and deformation history, while rock discontinuities vary with joint width, infilling type, and surface characteristics, influencing bulk rock behaviour. Elastic wave methods offer a non-destructive approach to characterising rock joints. This study investigates ultrasonic P-wave velocities across inclined joints filled with sand and clay using artificial joints prepared from granite cores. A comprehensive testing series considered joint inclination, type of infilling material, and water content. Results show a consistent polynomial relationship between P-wave velocity and joint inclination. Velocities varied with infilling properties such as grain size, hardness, porosity, and water content, with dry talc causing the greatest reduction in velocities. Increased water content in infillings mitigated velocity reductions, particularly in clay-filled joints, and a time-dependent increase in velocities from wet infillings was also observed. These findings provide new insights into the hydromechanical coupling of P-wave velocities and infilling properties, expanding the application of elastic wave measurements for understanding rock behaviour and geophysical investigations.