Submarine landslides involve the interaction of a sliding soil mass, surrounded by fluid and an underlying, relatively stationary ground surface. Traditionally much of the research on submarine slides has focused on describing the moving soil as a viscous material with frictional resistance developed between the moving soil and underlying ground surface. This research has generally not been able to explain the relatively long run-out distances that many submarine slides exhibit. Recently hydroplaning has been proposed as a potential mechanism for describing the slide movements and appears to be a major contributor to the large run-out distances exhibited by many submarine slides. The current research reported on here is focused on the mechanism of hydroplaning and in particular the influence of the fluid surrounding the moving slide mass.
Previous studies of hydroplaning of submarine slides have employed empirical equations and assumptions to describe the forces exerted by the fluid on the soil mass. This was reported on in the previous progress report for this project. Most of the empirical equations and assumptions have not been verified and in some cases there are contradictions between the theoretical models and experimental observations. For example, Mohrig, et al. (1998) found from model tests that the critical Froude number for hydroplaning is 0.35. This corresponds to the “lift” produced by the kinetic pressure on the front of the soil mass that is only 4.5 percent of the buoyant weight of soil. Mohrig’s observations on when the soil should lift off the underlying material and cause initiation of hydroplaning are not explained by the assumption that the only kinetic pressure on the front of the soil mass is the stagnation pressure at the bottom surface.
In this report, a numerical model is developed to simulate the flow around the sliding soil mass during hydroplaning and to examine the forces applied on the soil mass by the surrounding fluid. In the following sections the basic assumptions made, the numerical modeling techniques employed and the software used for implementation are described. Various cases considered for numerical modeling are presented and the results are described. Finally, important observations and conclusions about the interaction between the fluid and moving soil mass are presented.