Abstract
The mechanism underlying the generation of fluid mud by wave action is examined theoretically and experimentally. Experiments were made in a wave-current flume and an oscillating-water tunnel using two artificial cohesive sediments and a marine mud. The flume experiments indicated that fluid mud was generated by wave action if the wave height exceeded a threshold value. This value was found to increase with the consolidation period. Wave-averaged porewater pressures measured at the onset of liquefaction showed a transient decrease followed by a gradual build-up of an excess pressure. This is ascribed to the break-up of the aggregate structure (transient decrease) and compensation of reduced effective stresses (excess porewater pressure). Theoretical analysis shows that under normal conditions the maximal pressure-induced shear stress in a finite layer of a consolidated mud, modelled as a poro-elastic material, is much greater than the shear stresses at the bed surface caused by the oscillating flow. If the pressure-induced shear stress in the bed exceeds the yield strength of the mud at a particular level in the bed, the aggregate structure breaks up and the mud liquefies.
Published Version
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