Is elastic wave velocity a proxy for fabric evolution under shear in quartz sand? An experimental study using X-ray tomography and ultrasonic transducers

Understanding the link between the evolution of fabric and elastic wave velocity in sand subjected to shear is of critical significance in engineering practice. To achieve this objective, an innovative multiscale experimental campaign was conducted by integrating triaxial compression with simultaneous wave velocity measurements and X-ray computed tomography. Discrete digital volume correlation (DDVC) was employed to measure particle kinematics and combined with contact detection algorithms to characterise contact-based fabric. The results revealed clear correlations of elastic wave propagation, fabric evolution and strain localisation development during shearing. Three distinct stages of the shear process were observed. Based on effective medium theory, the stress normalised wave velocity was found to positively correlate with the coordination number contributed in the wave propagation direction after accounting for contact normal anisotropy and void ratio, exhibiting a relatively unified relationship. This study provides experimental evidence for a strong correlation between normalised wave velocity and selected fabric descriptors, offering a potential basis for improving the calibration and validation of discrete-element simulations of sheared granular media.