Laboratory Study of Liquefaction due to Wave–Seabed Interaction

Objects placed on the seabed sink in because of the momentary liquefaction of the seabed due to wave loading. The depth of the momentary liquefaction depends on the pore pressure propagation which is governed by wave and seabed properties. A large-scale one-dimensional experimental investigation program was carried out with particular attention given to the momentary liquefaction of the seabed. Approximately a $1.4\mathrm{m}$ thick sand bed and a $1.1\mathrm{m}$ of water column above the sand bed were subjected to a series of waves. The experimental variables were sand bed density, degree of saturation, dynamic pressure amplitude, and frequency of wave loading. The measured pore pressure response within the sand bed was found to attenuate with significant phase lag, which increased the likelihood of the momentary liquefaction. Pore pressure response at a particular location within the sand bed was found to increase with an increase in wave period, an increase in degree of saturation, and an increase in permeability of the sand bed. With other parameters remaining the same, the likelihood of the momentary liquefaction of the seabed increases with decreasing wave period, decreasing degree of saturation, and decreasing permeability of the seabed. An object placed on the sand bed was found to progressively sink into the momentarily liquefied sand bed. The rate of sinking of the object during loading and unloading phases of waves was measured and discussed.