Onset Of Landslides Research Articles

Viscous flow around three-dimensional macroscopic cavities in a granular material: asymptotic theory for two sufficiently distant spherical cavities of arbitrary configuration

Viscous flow around two spherical macroscopic cavities (or void spaces) in a granular material, which is exposed to an otherwise uniform flow at infinity, is investigated. The flow field is obtained analytically by solving the Stokes equation inside and the Darcy–Brinkman equation outside of the cavities, where continuity of the velocity and that of the stress are assumed on the boundary. In our previous complementary paper (Sano, Karmakar & Sekhar, J. Fluid Mech., vol. 931, 2022, A20), we obtain that two cavities of equal size in a tandem position are more prone to collapse for a shorter centre-to-centre distance with low permeability. In the present study, the asymptotic analysis of the interaction of two spherical cavities of different sizes with arbitrary configuration is presented. Particular attention is paid to the configuration dependence of two cavities of equal radius. The velocity field and the volume flux into respective cavities are calculated, which reveal that two cavities with orientation less than a certain critical angle are given a larger volume flux and are more prone to collapse. The present results are applicable to predicting the behaviour in a fixed-bed regime of a solid–gas transport system, microscale waterway formation in a granular material, onset of landslides, collapse of cliffs and river banks, etc.

IDENTIFYING THE MAIN FEATURES OF LANDSLIDE MOVEMENT AND DEVELOPING THE BASIC MECHANISMS

The results of studies of the mechanisms and main features of the movement of fast and extended clayey and other landslides are presented. Landslides are said to cause about 1,000 deaths and $4 billion losses of property each year. However, at least 90% of all landslide losses could have been avoided if the problem had been recognized in advance. At present, as a result of a preliminary statistical analysis, results have been obtained that generally explain the occurrence of the onset of landslides. On their basis, three mechanisms were explained that cause the movement of the geomass of landslides: under the influence of gravitational forces, fluidization and lubrication of the landslide bed along the base of the main guides. However, additional research has found that those gravitational forces do not ensure the movement of significant geomasses over long distances. The third mechanism we have identified is the participation of nanoparticles of the lower layer of the moving landslide as natural nano-bearings. Halloysite nanoparticles have been studied, which are nanotubes (having a length of 0,5...2 μm and an outer diameter of about 200 nm, with a lumen diameter of 10...15 nm), in which sheets of aluminosilicate are coiled into a spiral. Typically, the shells of such hallusite pipes include 15...20 layers. In addition, halloysites, depending on the conditions of crystallization and geological structure, may have another morphology (such as, for example, spheroidal or disk), which also plays the role of nano-bearings that contribute to the movement of the landslide geomass.

Viscous flow around three-dimensional macroscopic cavities in a granular material

Viscous flow around spherical macroscopic cavities in a granular material is investigated. The Stokes equation inside and the Darcy–Brinkman equation outside the cavities are considered. In particular, the interaction of two equally sized cavities positioned in tandem is examined in detail, where the asymptotic effect of the other cavity is taken into account. The present analysis gives a reasonable estimate on the volume flow into the cavity and the local enhancement of stresses. This is applicable to predict the microscale waterway formation in that material, onset of landslides, collapse of cliffs and river banks, etc.

On the Field Estimation of Moisture Content Using Electrical Geophysics: The Impact of Petrophysical Model Uncertainty

AbstractThe spatiotemporal distribution of pore water in the vadose zone can have a critical control on many processes in the near‐surface Earth, such as the onset of landslides, crop yield, groundwater recharge, and runoff generation. Electrical geophysics has been widely used to monitor the moisture content (θ) distribution in the vadose zone at field sites, and often resistivity (ρ) or conductivity (σ) is converted to moisture contents through petrophysical relationships (e.g., Archie's law). Though both the petrophysical relationships (i.e., choices of appropriate model and parameterization) and the derived moisture content are known to be subject to uncertainty, they are commonly treated as exact and error‐free. This study examines the impact of uncertain petrophysical relationships on the moisture content estimates derived from electrical geophysics. We show from a collection of data from multiple core samples that significant variability in the θ(ρ) relationship can exist. Using rules of error propagation, we demonstrate the combined effect of inversion and uncertain petrophysical parameterization on moisture content estimates and derive their uncertainty bounds. Through investigation of a water injection experiment, we observe that the petrophysical uncertainty yields a large range of estimated total moisture volume within the water plume. The estimates of changes in water volume, however, generally agree within (large) uncertainty bounds. Our results caution against solely relying on electrical geophysics to estimate moisture content in the field. The uncertainty propagation approach is transferrable to other field studies of moisture content estimation.

Triggering and predisposing factors for flow-like landslides in pyroclastic soils: the case study of the Lattari Mts. (southern Italy)

Shallow flowslides, debris flows and debris avalanches are rainfall-induced landslides consisting in the shear failure of few metres of soils (or in some cases even less than a metre), which greatly increase downslope in volume and flow velocity. The southern Italian region of Campania has been historically affected by such events involving pyroclastic soils mainly resting on steep carbonate slopes. This paper deals with the analysis of factors influencing the occurrence of flow-like landslides, adopting the Lattari Mts. in Campania as a case study. The results of two investigation campaigns carried out in the area allowed effective large-scale geological and geotechnical characterization to be set up. Stratigraphic profiles, mean physical properties and typical friction angles at the critical state for each soil layer were investigated. The effect of suction on peak and critical shear strength, whose drop is responsible for soil failure, was analysed. Using detailed information on both the stratigraphic and geotechnical features of the soils involved in past flow-like landslides, typical triggering models were selected, representing locally recurrent geomorphologic conditions at the basin scale. The identified models were adopted for slope stability analyses carried out on four cross-sections of flowslides occurring prior to the event, to back-analyse the triggering conditions. From the evidence on the triggering mechanisms and the results of analyses, the infinite slope approach is not always suitable to model slope stability conditions properly, because the onset of landslides is also affected by local topographic and stratigraphic factors.

Physically based modeling of rainfall thresholds for the onset of landslides

Physically based modeling of rainfall thresholds for the onset of landslides

Effects of soil spatial variability at the hillslope and catchment scales on characteristics of rainfall‐induced landslides

AbstractSpatial variations in soil properties affect key hydrological processes, yet their role in soil mechanical response to hydro‐mechanical loading is rarely considered. This study aims to fill this gap by systematically quantifying effects of spatial variations in soil type and initial water content on rapid rainfall‐induced shallow landslide predictions at the hillslope‐ and catchment‐scales. We employed a physically‐based landslide triggering model that considers mechanical interactions among soil columns governed by strength thresholds. At the hillslope scale, we found that the emergence of weak regions induced by spatial variations of soil type and initial water content resulted in early triggering of landslides with smaller volumes of released mass relative to a homogeneous slope. At the catchment scale, initial water content was linked to a topographic wetness index, whereas soil type varied deterministically with soil depth considering spatially correlated stochastic components. Results indicate that a strong spatial organization of initial water content delays landslide triggering, whereas spatially linked soil type with soil depth promoted landslide initiation. Increasing the standard deviation and correlation length of the stochastic component of soil type increases landslide volume and hastens onset of landslides. The study illustrates that for similar external boundary conditions and mean soil properties, landslide characteristics vary significantly with soil variability, hence it must be considered for improved landslide model predictions.

Hard X-ray imaging for landslide research

Synchrotron phase-contrast hard X-ray imaging is used to provide highly efficient direct visualization of landslide dynamics and granular flows in fully wet granular piles. High penetration capability and phase-contrast enhancement of hard X-rays offer marked advantages in the precise tracking of individual granular movements through a thick water medium. It is revealed that the stress accumulation follows a power-law evolution while the relaxation follows an exponential one. The onset of landslide emerges at the trade-off of the two evolutions.

Numerical modelling of a slope stability test by means of porous media mechanics

PurposeThe purpose of this paper is to present a finite‐element analysis of the initiation of a slope failure in a small‐scale laboratory test due to pore pressure variation. To this aim, a fully coupled multiphase model for saturated/partially saturated solid porous materials based on porous media mechanics is used.Design/methodology/approachThe slope is described as a three‐phase deforming porous continuum where heat, water and gas flow are taken into account. The gas phase is modelled as an ideal gas composed of dry air and water vapour. Phase changes of water, heat transfer through conduction and convection and latent heat transfer are considered. The independent variables are: solid displacements, capillary pressure, gas pressure and temperature. The effective stress state is limited by Drucker‐Prager yield surface for the sake of simplicity. Small strains and quasi‐static loading conditions are assumed.FindingsThe paper shows that the multiphase modelling is able to capture the main experimental observations such as the local failure zone at the onset of slope failure and the outflow appeared in that zone. It also allows understanding of the triggering mechanisms of the failure zone.Research limitations/implicationsThis work can be considered as a step towards a further development of a suitable numerical model for the simulation of non‐isothermal geo‐environmental engineering problems.Practical implicationsThe multiphysics approach looks promising for the analysis of the onset of landslides, provided that the constitutive models for the multiphase porous media in saturated/unsaturated conditions and the related mechanical and hydraulic properties are described with sufficient accuracy.Originality/valueElasto‐plastic thermo‐hydro‐mechanical modelling of the initiation of slope failure subjected to variation in pore pressure boundary condition.

Some remarks on the recent conditions related to the development and prognosis of sliding movements in the flyschoid rocks of the West Carpathians

Recent natural conditions of central Europe give rise to sliding movements mostly due to the revival of older deformations. Spontaneous origin of deformations on undisturbed slopes in the absence of human activity is rare. In the Flysch area of the West Carpathians the tendency to the onset of landslides exists in the talus masses of hills and depressions, mostly on slopes inclined 7 to 15 degrees. With this the combination of hydrogeological and morphological conditions is most favourable for the development of failures. Natural origin of landslides in this case occurs mostly in the presence of extreme precipitation of the order of 250 to 300% of the average values and in the non-vegetation period, i.e. from October to March.