This paper describes finite element analyses of wave-induced liquefaction of sand beds. The authors were motivated by previous experimental results in which a series of centrifuge wave tank tests were performed on loosely packed fresh deposits of sand with viscous scaling introduced. The principal finding was that the resistance to liquefaction under progressive waves was considerably smaller than the resistance exhibited under standing waves. An important factor for this marked difference was suggested to be the rotation of the principal stress axes that occurs under progressive wave loading. The present study extends an existing cyclic-plasticity constitutive model to account for the effect of stress axis rotation of sands. This model was incorporated into a finite element analysis procedure, which was applied to soil responses to progressive wave and standing wave loading. The predicted results compare well with observed soil behaviour. The predicted effective stress paths and associated stress–strain ...

Analysis of wave-induced liquefaction of sand beds

On 28 September 2018, a strong earthquake with a moment magnitude of 7.5 occurred on the island of Sulawesi, Indonesia. This earthquake caused extensive liquefaction and liquefaction-induced flow slides inland. Despite a strike-slip fault, which typically displaces land horizontally, being unlikely to produce significant tsunamis, the earthquake in fact caused devastating tsunamis. Our field investigations showed that there was an occurrence of extensive liquefaction in coastal areas. Significant coastal liquefaction can result in a gravity flow of liquefied soil mass that can cause a tsunami. A comparison with a past disaster of the strike-slip fault Haiti earthquake tsunami indicated that essentially the same occurred at the Palu coast of Central Sulawesi. Namely, liquefaction-induced total collapse of coastal land caused liquefied sediment flows, resulting in a tsunami. An important difference between this time and Haiti was that such total collapses and flows of coastal land due to liquefaction occurred at several (at least nine) places, resulting in multiple tsunamis. Analysis of the tidal data implied that less than 20% of the tsunami height was related to tectonic processes, and the majority was caused by the coastal and submarine landslides as characterized by liquefied gravity flows.

/pdf/liquefied-gravity-flow-induced-tsunami-first-evidence-and-19efe81c2x.pdf

Liquefied gravity flow-induced tsunami: first evidence and comparison from the 2018 Indonesia Sulawesi earthquake and tsunami disasters

Landslide-generated waves (LGWs) are among natural hazards that have stimulated attentions and concerns of engineers and researchers during the past decades. At the same period, the application of numerical modeling has been progressively increased to assess, control, and manage the risks of such hazards. This paper represents an overview of numerical studies on LGWs to explore associated recent advances and future challenges. In this review, the main landslide events followed by an LGW hazard are scrutinized. The uncertainty regarding landslide characteristics and the lack of data concerning generated tsunami properties highlights the necessity of probabilistic analysis and numerical modeling. More than 53 % of landslides show the slide length larger than about 20 times of the slide thickness. This fact justifies the popular application of depth-averaged equations (DAEs) for landslides’ motion simulations. Such models are reviewed and tabulated based on their mathematical, numerical, and conceptual approaches. A landslide is generally treated as a homogeneous, mixture, or a multi-phase fluid with different rheologies. The Coulomb type rheology is the most-used rheology applied in more than 70 % of landslide models. Some of the recent studies are considering the effects of multi-phase nature, dynamic changes of rheological parameters, and grain-size segregation of the landslide on its deformations. The numerical tools that model LGWs are also reviewed, categorized, and examined. These models conceptualize a landslide as a general rigid LGW (R-LGW) or deformable LGW (D-LGW) mass. The rigid slide assumption is mainly applied in the LGW models with a focus on the accurate simulation of the wave propagation stage, particularly by means of higher order Boussinesq-type wave equations (BWEs). The majority of D-LGW models solve either the Navier–Stokes equations (NSEs) for a multi-phase (landslide material, water, and air) flow or the shallow water equations (SWEs) for a two-layer (a layer of granular material moving beneath a layer of water) flow. NSEs are more comprehensive models but less robust than DAEs. The key effect of dispersion in LGWs, which are typically important in intermediate and even deep water wave domains, challenges researchers to apply higher order BWEs instead of SWEs in two-layer models. Regarding numerical approaches, Lagrangian’s are more robust than Eulerian’s, but they have been rarely applied due to their high computational demands for real cases. The remaining challenges are reviewed as the necessity of probabilistic analysis to assess the risk of the related hazards more accurately for both past and potential LGW hazards; further thorough laboratory-scale experiments and field data measurements to have accurate and detailed benchmark data; providing RS/GIS-based worldwide hazard map for potential LGWs and compiled database for occurred events; extending BWEs for granular flows and DAEs with non-hydrostatic corrections; and economizing the computational costs of models by advanced techniques like parallel processing and GPU accelerators.

Numerical modeling of subaerial and submarine landslide-generated tsunami waves—recent advances and future challenges

Wave-Induced Seabed Response in an Isotropic Seabed.- Wave-Induced seabed Instability.- Cross-Anisotropic Soil Behavior.- Non-Homogeneous Seabed.- Wave-Driven Seepage flux in Marine Sediments.- Dynamic Analysis for Wave-Seabed Interactions.- Wave-Induced Pore Pressure Accumulation in Marine Sediments.- Dynamic Analysis for Wave-Seabed Interactions.- Dynamic Analysis for Wave-Seabed Interactions.- Wave Propagation over Coulomb-Damped Seabed.- Wave-Induced Pore Pressure Accumulation in Marine Sediments.- Random wave-induced seabed response 295.- Wave-Induced Progressive liquefaction in a porous seabed.- Poro-Elastoplastic model for Wave-Seabed Interactions.- Response of Seabed to Combined Wave and Current Loading.- ANN model for Wave-Induced Liquefaction 341.- Models for Wave-Seabed-Structure Interaction.

Porous Models for Wave-seabed Interactions

Wave-induced sea floor dynamics

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...

Wave-induced liquefaction of beds of sand in a centrifuge

The propagation of liquefied zones in sand beds under fluid-wave loading is theoretically analysed in the present study. The completely liquefied state of sand is modelled as an inviscid fluid of a particular density, and the underlying sub-liquefied soil is modelled as a poro-elastoplastic material obeying a simple law of cyclic plasticity. It is shown that the proposed theoretical model is capable of consistently predicting the prograssive nature of liquefaction as observed in centrifuge wave tank tests on loose deposits of fine-grained sand. The theoretical model can also predict the final depth of the liquefaction front under a given wave loading.

Analysis of progressive liquefaction as a moving-boundary problem

A theoretical model for progressive solidification is described. It reproduces the experimental finding, from centrifugal wave tank testing with viscous scaling, that a layer of liquefied sand solidifies progressively from the base up while severe fluid-wave loading is imposed over a prolonged period of time. The solidification process reestablishes a grain-supported framework in the transitory fluid-like soil and is accompanied by the marked densification and gradual dissipation of excess pore pressures in a zone immediately below the upward-advancing solidification front. The continued disturbances to liquefied soil in the form of wave loading are an effective means for loosening the interlocking of solid particles, and permit rearrangement into a state of remarkably dense compaction due to contractancy. These aspects of soil behaviour are accentuated through comparison with consolidation in quiescent conditions following liquefaction. Furthermore, the proposed rigorous treatment of solidification as a ...

Shinji Sassa

Papers

Wave-induced liquefaction of beds of sand in a centrifuge

Analysis of wave-induced liquefaction of sand beds

Liquefied gravity flow-induced tsunami: first evidence and comparison from the 2018 Indonesia Sulawesi earthquake and tsunami disasters

Analysis of progressive liquefaction as a moving-boundary problem

Progressive solidification of a liquefied sand layer during continued wave loading