The sequence of sediment behaviour during wave‐induced liquefaction

TLDR

The study experimentally investigates the full sequence of sediment behavior under progressive waves. The experiment used a silty sediment (d50 = 0.060 mm) in a 42‑cm deep tank, measuring pore‑water pressure, water‑surface elevation, and video to track mudline, liquefaction/compaction fronts, and orbital motion across wave heights 9–17 cm, period 1.6 s, Shields 0.34–0.59. The experiments show that wave action generates excess pore pressure leading to liquefaction with internal waves, followed by pressure dissipation, compaction, and bed‑ripple formation, and that ripple steepness is unchanged by prior liquefaction.

Abstract

Abstract This paper presents the results of an experimental investigation of the complete sequence of sediment behaviour beneath progressive waves. The sediment was silty with d 50 = 0.060 mm. Two kinds of measurements were carried out: pore‐water pressure measurements (across the sediment depth), and water‐surface elevation measurements. The process of liquefaction/compaction was videotaped from the side simultaneously with the pressure and water‐surface elevation measurements. The video records were then analysed to measure: (i) the time development of the mudline, (ii) the time development of liquefaction and compaction fronts in the sediment and (iii) the characteristics of the orbital motion of the liquefied sediment including the motion of the interface between the water body and the sediment. The ranges of the various quantities in the tests were: wave height, H = 9–17 cm, wave period, T = 1.6 sec, water depth = 42 cm, and the Shields parameter = 0.34–0.59. The experiments reveal that, with the introduction of waves, excess pore pressure builds up, which is followed by liquefaction during which internal waves are experienced at the interface of the water body and the liquefied sediment, the sequence of processes known from a previous investigation. This sequence of processes is followed by dissipation of the accumulated excess pore pressure and compaction of the sediment which is followed by the formation of bed ripples. The present results regarding the dissipation and compaction appear to be in agreement with recent centrifuge wave‐tank experiments. As for the final stage of the sequence of processes (formation of ripples), the ripple steepness (normalized with the angle of repose) for sediment with liquefaction history is found to be the same as that in sediment with no liquefaction history.