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 sea floor dynamics

Particle methods in ocean and coastal engineering

This paper presents the results of an experimental investigation of the complete sequence of sediment behaviour beneath progressive waves. The sediment was silty with d50 = 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.

The sequence of sediment behaviour during wave-induced liquefaction

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 ...

Progressive solidification of a liquefied sand layer during continued wave loading

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

This paper discusses the floatation of a buried pipe in association with wave-induced liquefaction of sand beds. Centrifuge wave tests in a drum channel were performed with viscous scaling ...

https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%29WW.1943-5460.0000547

Wave-Induced Liquefaction and Floatation of a Pipeline in a Drum Centrifuge

The Tohoku coastal area in Japan suffered massive damage in the Great Tohoku Earthquake, in which a prolonged major earthquake was followed by a large tsunami. The damage mechanisms of coastal structures during earthquake–tsunami events have not been fully explained. Thus, this study elucidates the damage mechanism of breakwaters by focusing on the interactions among earthquake–tsunami events, caisson structures, and soil composed of rubble mounds and seabed components. Centrifuge model tests, finite-element analyses, and smoothed particle hydrodynamics simulations with tsunami–soil–structure interactions were performed. The simulated breakwater was destabilized by not only wave pressure, but also long-acting tsunami seepage flow and overflow into the rubble mound and the seabed. These processes resulted in scour and fluidization/liquefaction, which decreased the bearing capacity. Moreover, the liquefaction resulting from earthquake motion caused caisson subsidence and excess pore water pressure i...

Instability of a Caisson-Type Breakwater Induced by an Earthquake–Tsunami Event

The propagation of solidified zones in the course of subaqueous liquefied sediment flow is theoretically discussed The coupled systems of Navier-Stokes equations and consolidation equation are numerically solved under moving boundary conditions, with consideration of the concurrent evolutions of the flow surface as well as of the internally formed interface between the fluid and solidified zones The analyses for collapse of a body of liquefied soil into ambient fluid under gravity show that the liquefied sediment flow manifests itself as a decelerating gravity flow due to the dynamic interaction between the flowing liquefied soil and the progressively solidified zones in the sediment

Junji Miyamoto

Papers

Analysis of progressive liquefaction as a moving-boundary problem

Progressive solidification of a liquefied sand layer during continued wave loading

Wave-Induced Liquefaction and Floatation of a Pipeline in a Drum Centrifuge

Instability of a Caisson-Type Breakwater Induced by an Earthquake–Tsunami Event

The Dynamics of Liquefied Sediment Flow Undergoing Progressive Solidification