Experimental study on the relation between compressional wave velocity and physical properties of sandy sediments

Sand is one of the main type of submarine sediments. Figuring out the relation between acoustic and physical properties of sandy sediments is critical to seafloor and sub-bottom detection. In this paper, by using the ultrasonic detector and the self-developed sample preparation device, sand samples in different physical states are prepared to simulate different natural sedimentary conditions. Acoustic and physical properties are tested simultaneously, so as to reveal the effective measuring methods and its influence factors, and to explore the internal connection between the compressive wave velocity (CWV) and physical parameters of sandy sediments. Results and analysis indicate that the multipath propagation of sound wave can affect the measurement accuracy for the method with ultrasonic transducers touching the side wall of sediment container, while this effect can be avoided by measuring with a direct contact between transducers and sediment. No effects are found with different test frequencies among 30 kHz to 100 kHz. The CWV of sandy sediments, which shows good correlation with density, porosity and water content, with correlation coefficients 0.87, 0.86, and 0.84, respectively, increases with increasing density, while decreases with increasing porosity and water content. While the correlation coefficient between CWV and medium diameter is smaller than 0.6, which shows that the CWV of sandy sediments has no clear link to grading distribution. The correlation of acoustic impedance with bulk density, porosity and water content is bigger than that of CWV with them. In addition, special attention should be paid to the saturation of sediments because the CWV is very sensitive to saturation, for example, the CWV increases dramatically from 393.3 m·s⁻¹ to 748.5 m·s⁻¹ as the saturation increases from 0.971 to 0.994.