Wave-induced liquefaction of beds of sand in a centrifuge

Abstract

The behaviour of beds of fine-grained sand under fluid wave trains was investigated using centrifuge modelling. Three sets of centrifuge wave tank tests with viscous scaling were performed, such that time-scaling laws for wave propagation as well as consolidation were matched. The test programme consisted of either progressive- or standing-wave tests on loosely packed, fresh deposits of soil, as well as repeated travelling-wave tests with intervening periods of consolidation. The results from the progressive- and standing-wave tests indicate that for each of the wave-loading regimes, there exists a critical cyclic stress ratio below which liquefaction does not occur. The critical value for the progressive-wave-loading series was found to be considerably smaller than that for the standing-wave-loading series. Moreover, the wave-induced liquefaction of the sand beds was of a progressive nature. In fact, under the action of severe travelling waves, liquefaction was first induced in the uppermost layer of the sand bed, and then the liquefaction front advanced downward in the course of wave loading, eventually bringing the entire soil bed into a state of complete liquefaction. It is also shown from the repeated wave tests that the liquefied beds of soil underwent significant densification in the consolidation processes that followed. In each of the subsequent wave-reloading stages, re-liquefaction was observed to occur in such a way that the final depth of the liquefaction front became shallower. Nous avons étudié le comportement ďun banc de sable fin soumis à des trains ďondes fluides en utilisant une maquette centrifuge. Nous avons conduit trois lots ďessais en bac centrifuge avec échelle de viscosité, de facon à lui faire correspondre les lois ďéacchelle de temps šappliquant à la propagation des ondes tout comme à la consolidation. Le programme ďessais consistait de tests ďondes progressives et d'ondes stationnaires passant sur des dépôts de sol frais, non compacté ; le programme comportait aussi des essais répétés ď'ondes progressives avec des périodes intermittentes de consolidation. Les résul- tats des essais ďondes progressives et ďondes stationnaires indiquent que pour chacun des régimes de charges ďondes, il existe un taux de contrainte cyclique critique en dessous duquel la liquéfaction ne se produit pas. On a constaté que la valeur critique pour la série de charges ďondes progressives était bien inférieure à celle de la série de charges ďondes stationnaires. De plus, la liquéfaction des bancs de sable causée par les ondes était de nature progressive. En fait, sous ľaction ďondes fortement progressives, la liquéfaction se produisait ďabord dans la couche supérieure du banc de sable, puis le front de liquéfaction avancait au cours de la charge ďondes, mettant finalement le banc de sol ender dans un éat de liquéfaction totale. Nous montrons également, en nous basant sur les essais ďondes répétés que les bancs de sol liquéfiés subissent une densification significative au cours des processus de consolidation qui solvent. Dans chacun des stades suivants de recharges ďondes, nous avons observé qcune nouvelle liquéfaction se produisait de telle manière que la profondeur finale du front de liquéfaction diminuait.

Liquefaction potential of coastal slopes induced by solitary waves

“…They concluded that pore water pressure fluctuations in the seabed due to short period waves are significant and are affected by the soil permeability and deformability, and wave-induced liquefaction is related to the upward seepage flow induced in the sea bed during the passage of wave troughs [16]. To understand the soil behavior in a controlled setting, wave tank experiments [14,19,33,39,41,42,47], compressive tests [12,51], and centrifugal wave tank studies [29,30,32] have also been conducted. Wave tank experiments have the advantage that they can provide the spatial and temporal distribution of the wave-induced pressures at the structure and at the bed surface.…”

“…To overcome the 1g limitation and to provide spatial distribution of the wave loads, Sekiguchi and Phillips [32] and Phillips and Sekiguchi [29] developed a novel setup to conduct wave experiments in a centrifuge. Viscous scaling was used to satisfy the time-scaling laws for fluid wave propagation and the consolidation of the soil [30]. However, the study was limited to short period progressive or standing waves with an equivalent field period of 4.5 s over a flat bottom.…”

“…The MC model cannot capture the necessary volumetric compaction in order to model this process. See, for example, Sassa and Sekiguchi [30], Dunn et al [15], and Ou et al [28] for the numerical studies of this cyclic liquefaction behavior using more sophisticated elastoplastic models. In the current study, however, the primary liquefaction mechanism is instantaneous rather than cyclic.…”

Pore Water Infiltration and Drainage on a Megatidal Beach in Relation to Tide- And Wave-Forcing

“…Sakai et al (1992) reported sinking concrete blocks at a beach in Japan, and proved that liquefaction is a theoretically consistent explanation for the observed beach sediment instability. Such theories were supported by laboratory studies by, e.g., Clukey et al (1985); Sassa and Sekiguchi (1999).…”

“…1), as well as vibration of structures or seismic activity. Since the 1990s researchers have successfully demonstrated and investigated this effect in wave tanks and numerical simulations (Sakai et al, 1992;De Wit and Kranenburg, 1997;Sassa and Sekiguchi, 1999;Osinov, 2000;Sassa and Sekiguchi, 2001;Jeng et al, 2004;Mutlu Sumer et al, 2006). Momentary liquefaction has gained in importance regarding observations of unexpectedly strong erosion, for example at beaches during storm events and in connection with scour.…”