S-Wave Velocity-Stress Power Relationship: Packing and Contact Behavior of Sand Specimens

The S-wave velocity in particulate materials depends on the state and history of the effective stresses, void ratio, degree of saturation, and type of particles. Based on experimental evidence and analytical studies, the velocity-effective stress relationship for granular materials is expressed as a power function having two physically-meaningful parameters: a coefficient α and an exponent β. These parameters represent the S-wave velocity at a given state of stress and its variation with stress changes. This experimental study presents velocity-stress power relationship for interpreting the packing and contact behavior of sand. Dry medium sand specimens were prepared by five methods of specimen preparation: (1) scooping, (2) tamping, (3) rodding, (4) vibrating, and (5) pluviating, representing five different packings. The S-wave velocities of these sand specimens were measured using bender elements under isotropic state of stress. Results indicate that the coefficient α correlates fairly well with the type of packing (i.e., void ratio or coordination number) and particles' physical properties and that the values of exponent β agree with the semi-empirical values predicted for rough particle contacts and are within the expected range for loose to dense sand.