Analysis on acoustic velocity characteristics of sediments in the northern slope of the South China Sea

To understand the spatial characteristics of the acoustic velocity within sediments in the northern slope of the South China Sea, an ultrasonic technique was employed to measure the vertical and horizontal acoustic velocities of sediment core samples. Combined with the physical and mechanical properties test results of sediments, the relationships between acoustic velocity and physical properties were analyzed. The research results showed that the acoustic velocity presented irregular variations at the same depth among different stations, and that, in general, the acoustic velocities in the vertical direction were greater than those in the horizontal direction. For different sampling stations and different depths, the acoustic velocities showed a great variability; they exhibited large differences and there was almost no relation between the vertical and horizontal velocities. In addition, the results clearly exhibited strong anisotropic characteristic among the acoustic velocities. This variation of acoustic velocity was due to complex changes of physical and mechanical properties of seabed sediments in the study area. The results of the study also showed that there was a large deviation between the measured and the predicted acoustic velocities. The predicted results were calculated by empirical equations using the relationships between single geotechnical parameters and the acoustic velocity. The research results improve the understanding of engineering geological properties of the sediments in the study area.