An experimental investigation into the evolving instability of a subaqueous mild silty slope under progressive waves
The silty sediments that are widely distributed in estuaries and deltas are susceptible to slope instability due to ocean storms. Flume experiments were carried out in this study to investigate the characteristics and failure process of a subaqueous mild silty slope subjected to ocean waves. The results show that the wave steepness varies accordingly to wave propagation over the mild silty slope due to shoaling effect. Where the wave steepness is up to the threshold value of 0.04, liquefaction may occur in silty slopes due to the substantial amount of residual pore water pressure development. In this process, the maximum wave pressure appears near the wave breaking point where it may be increased by about 40% compared with that at bottom of the slope; this means that liquefaction may primarily first occur in regions near the wave breaking point and become the predominant trigger for the overall slope instability. The maximum liquefaction and sliding depth of silty seabed may reach 0.1–0.15 times the wavelength for wave steepness of 0.04–0.10. Unlike the failures of a loose sandy slope that are characterized by a slumping stage along with a sudden rise in pore water pressure, wave induced failure of the mild silty slope progresses in three distinct stages, i.e., (i) initial erosion and scouring, (ii) coupled development of liquefaction and scour, and (iii) oscillating and sliding of sediments.
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Australian Research Council