Effect of history of wave exposure on seabed liquefaction

This paper presents the results of an experimental investigation of wave-induced liquefaction in the case of multiple wave exposures. The experiments include also standard progressive wave cases as well, for comparison. One kind of sediment was used in the experiments: silt (d50=0.070 mm). Four scenarios were tested with multiple wave-climate exposures, including (1) multiple wave climates separated with “quiet”, no-wave periods, and (2) those with no interruptions between the consecutive wave-climate exposures, resembling a storm situation. It was found that the first strongest wave climate (i.e., the first wave climate, which is strong enough to cause liquefaction) of a multiple wave-climate sequence “secures” the onset of liquefaction, independent of prior wave exposures. It was also found that the wave exposures following the “liquefying” wave (even with stronger wave properties) do not liquefy the soil. The experiments further showed that, after the completion of the liquefaction-compaction cycle, the pore pressure may still build up when the soil is exposed to a new wave climate in the sequence with an even stronger set of wave characteristics (wave height and wave period). However, the accumulated pore pressure will not be large enough to liquefy the soil. Likewise, after the completion of the liquefaction-compaction cycle, or after exposures to not one but a number of waves, again, even with stronger wave characteristics, the pore pressure may not even build up at all. The experiments shed further light on the circumstances in the field under which (1) the seabed soil would eventually become liquefaction resistant (with a very large relative density), and those under which (2) it would remain loose, both of which have been revealed by field surveys. Furthermore, it was found that, in the case when the wave-climate exposures are uninterrupted, the dissipation of the accumulated pore pressure is quite slow when compared with the situation where the wave-climate exposures are interrupted with “quiet”, no-wave periods. The results have been explained in terms of physical processes involved. Also, implications of the results for practice have been discussed in detail.