The effects of clay content on the dynamics of submarine landslides: New insights from flume experiments

Regarding whether submarine landslides' mobility decreases linearly or varies non-monotonically with increasing clay content in current studies is still under debate. To address this issue and further investigate the long-runout distance mechanism of submarine landslides, we conducted experiments with clay content ranging from 5% to 30% in a flume with an inclination angle of 10°. Through analysis of the rheological properties of the sediment slurry, the pore pressure and the total stress at the bed bottom along the channel, and the flow velocities, the dynamics of the submarine landslide were characterized. The experiments show that as the clay content increases, the flow transits from liquid-like to solid-like behavior. The peak values of both the pore pressure and the total stress, and the pressure loading rate at the bed bottom monotonically increase as the clay content increases. The velocity analysis supports the conclusion of a non-monotonic variation of mobility, which refers to the flow velocity exhibiting an initial increase followed by a subsequent decrease with the increase of clay content. The critical clay content, at which the maximum flow velocity occurs, is within the range of 10~15%. The mechanism analysis shows that the submarine landslide with the critical clay content has both lower apparent viscosity and higher pore pressure that is sufficient to generate hydroplaning, resulting in the highest mobility. The dimensional analysis shows that the dimensionless yield stress positively correlates to the clay content. It is also found that within the range of approximately three orders of magnitude from 5×10^-3 to 3, the dimensionless yield stress and the densimetric Froude number (Fr_d) exhibit a non-monotonic relationship, which also supports a non-monotonic behavior of the mobility. In summary, this study enhances our understanding of submarine landslide processes and further contributes to better disaster prediction.