1,720,967 research outputs found
Analytical and numerical models of debris flow impact
Full text linkA full understanding of the interaction mechanisms among flow-like landslides and impacted protection structures is still an open issue. Although several approaches, from experimental to numerical, have been used so far, a thoroughly assessment of the hydromechanical behaviour of the landslide body is achievable only through a multiphase and large deformation approach. This paper firstly proposes a conceptual model for a specific type of protection structure, namely a Deformable Geosynthetics-Reinforced Barrier (DGRB), i.e., an embankment made of coarse-grained soil layers reinforced by geogrids. In such a case, the sliding of the barrier along its base, under the impulsive action of a flow-type landslide, is an important landslide energy dissipation mechanism, and a key issue for the design. Then, two different approaches are proposed: i) an advanced hydro-mechanical numerical model based on Material Point Method is tested in simulating the whole complex landslide-structure interaction mechanisms, ii) an analytical model is set up to deal with the landslide energy dissipation and the kinematics of both the landslide and barrier. The calibration of the proposed analytical model is pursued based on the numerical results. Finally, the analytical model is successfully validated to interpret a large dataset of landslide impact field evidence, for whose interpretation also five empirical methods available in the literature are tested
Empirical formulation for debris flow impact and energy release
No full textFull understanding the interaction mechanisms between flow-like landslides and the impacted protection structures is an open issue. While several approaches, from experimental to numerical, have been used so far, it is clear that the adequate assessment of the hydromechanical behaviour of the landslide body requires both a multiphase and large deformation approach. This paper refers to a specific type of protection structure, namely a rigid barrier, fixed to the base ground. Firstly, a framework for the Landslide-Structure-Interaction (LSI) is outlined with special reference to the potential barrier overtopping (nil, moderate, large) depending on the features of both the flow and the barrier. Then, a novel empirical method is casted to estimate the impact force on the barrier and the time evolution of the flow kinetic energy. The new method is calibrated by using an advanced hydro-mechanical numerical model based on the Material Point Method. The validation of the empirical formulation is pursued referring to a large dataset of field evidence for the peak impact pressure. Both numerical and empirical methods can appropriately simulate the physical phenomena. The performance of the newly proposed empirical method is compared to the literature methods and its advantages are outlined
MPM-modelling of Reinforced-Concrete walls as protection structures against flow-like landslides
No full textThe use of massive protection structures against flow-like landslides, such as Reinforced Concrete (RC) walls, has been tested especially for rockfalls and to reduce the kinetic energy of boulders. In some contexts of debris flows, similar mitigation strategies have been pursued through cluster of blocks or baffles, especially in Asia. But it is still challenging: 1) the assessment of hydro-mechanical behavior of the landslide body, which is a mixture of solid skeleton saturated with water, during the impact; 2) to consider that protection works are always somehow deformable. Thus, both a multiphase approach and a large deformation formulation are fundamental to properly simulate the kinematics of the flowing material during the impact. This paper provides a contribution using the Material Point Method (MPM) numerical approach to the case of landslide of flow type impacting different types of protection structures, made of steel-reinforced concrete elements. The landslide is assumed with a non-zero initial velocity, and saturated. The landslide motion, the interaction with the structure and the base soil, and the final landslide deposition are simulated for a range of scenarios
Modelling the spatio-temporal evolution of a rainfall-induced retrogressive landslide in an unsaturated slope
Full text linkNumerical modelling, particularly fully-coupled hydro-mechanical large-deformation models, greatly helps in properly simulating the complex failure and post-failure mechanisms of rainfall-induced landslides. The affected soils, in fact, evolve from none or small deformation rates to large deformation rates during the initiation stage and vice-versa during deposition, with relevant interactions between the solid skeleton and interstitial water. The Material Point Method (MPM) has the potential to reproduce entirely those complex processes. However, a comparison with standard tools (e.g. FEM: Finite Element Method, LEM: Limit Equilibrium Method) may guide in the optimal choice (or in the combined use) of the various modelling approaches. A framework is here proposed based on a multi-tool approach consisting in the combination of: a) no-deformation LEM, b) small-deformation FEM, c) large-deformation MPM. The LEM slope stability analyses are performed for a realistic assessment of the major slip surface(s) and to back-analyse uncertain slope parameters. The FEM stress-strain analyses assess the progressive failure, the onset of initial velocity and the later acceleration of the landslide body, until large deformations occur in the slope and numerical convergence of FEM is lost. The MPM analyses are used to reproduce the whole landslide process, from the initiation to propagation and final deposition. Such an integrated framework is tested for an international landslide benchmark (the 1995 Fei Tsui Road landslide in Hong Kong). The results achieved through the different approaches are discussed in relation to the wide scientific literature available for the general topics and the specific case study. The paper highlights that the fully-coupled hydro-mechanical large-deformation model properly reproduces the complex failure and post-failure mechanisms of rainfall-induced landslides. However, no-deformation LEM analyses and small-deformation FEM analyses allow a reasonable understanding of both the pre-failure stage and the failure mechanism. These more traditional tools are confirmed as indispensable tools in the engineering practice and research
Inception of Debris Avalanches: A Material Point Method Modelling
No full textRainfall-induced landslides of the flow type in granular soils are among the most complex natural hazards due to the variety of mechanisms which regulate the failure and propagation stages. Among these, debris avalanches are characterised by distinct mechanisms which control the lateral spreading and the increase in soil volume involved during the propagation. Two different stages can be individuated for debris avalanches, i.e. the failure stage and the avalanche formation stage: the former includes all the triggering mechanisms which cause the soil to fail; the latter is associated to the increase of the unstable volume. Regarding these issues, in the literature, either field evidence or qualitative interpretations can be found while few experimental laboratory tests and rare examples of geomechanical modelling are available for technical and/or scientific purposes. In this paper a contribution is provided about the advanced numerical modelling of the inception of such hazardous debris avalanches. Particularly, the case of the impact of a failed soil mass on stable deposits is considered. This means that a small translational slide occurs; the failed mass causes the soil liquefaction of further material by impact loading; the landslide volume increases inside triangular-shaped areas during the so-called “avalanche formation”, and also soil erosion along the landslide propagation path plays an important role. To this aim, an innovative numerical technique known as the Material Point Method (MPM) is used. It can be considered as a modification of the well-known Finite Element Method (FEM) particularly suited for large deformations. The continuum body is schematized by a set of Lagrangian points, called Material Points (MPs). Large deformations are modelled by MPs moving through a background mesh, which also covers the domain where the material is expected to move. The MPs carry all physical properties of the continuum such as stress, strain, density, momentum, material parameters and other state parameters, whereas the background mesh is used to solve the governing equations without storing any permanent information. Such advanced approach allows combining a hydro-mechanical coupled approach, any of the well-known soil constitutive models proposed over the years in soil mechanics and a large-displacement formulation. The numerical analyses are performed adopting 2D geometrical configurations taken from field evidences and previous researches. Triangular 3-noded computational meshes are used, characterized by elements of about 1 m. The interaction between the impacting mass, and then of the propagating flow with the in-situ stable soil is examined, providing important insights about the behaviour of such type of landslide. The results achieved so far are encouraging and show that MPM can properly simulate the inception of debris avalanches and even their complex mechanisms during the impact and the interaction with in-situ stable zones
Possible remediation of impact-loading debris avalanches via fine long rooted grass: an experimental and material point method (MPM) analysis
No full textDebris avalanches often originate along steep unsaturated slopes and have catastrophic consequences. However, their forecast and mitigation still pose relevant scientific challenges. This is also due to the variety of mechanisms observed near high sub-vertical bedrock outcrops, such as the impact loading of soil failed upslope the outcrop, the build-up of pore water pressures in the inception zone, and the bed entrainment along the landslide propagation path. At the University of Salerno, an experimental and numerical investigation campaign started some years ago to explore the feasibility of using long-root grass to mitigate or even inhibit the inception of debris avalanches. Previous laboratory results were achieved through two twin 2-m-long columns (one bare, one vegetated), where the change in soil retention curve and soil mechanical response was assessed. As follow-up, an experimental field setup was installed in 2020 first, and in an improved configuration in 2021. Here, three different species of long-root grass were grown. In situ soil suction and water content measurements were periodically collected in the vegetated and in the original soils. In both cases, soil specimens were also collected, and laboratory geotechnical tests were performed to individuate the changes in both the water retention and strength response. Increased values of soil suction and shear strength were outlined, despite some differences, for all the grown species compared to the original soil. Using these novel experimental data, advanced large-deformation stress–strain hydro-mechanically coupled analyses were recently performed through a material point method (MPM) approach. The original slope conditions were compared to various slope configurations engineered via long-root grass. The benefits and the open issues related to this novel green technology for landslide mitigation are discussed. Some insights are outlined for the possible reduction of the soil volumes mobilized inside the inception zone of debris avalanches
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Transplant with MZ genotype liver: what is the clinical pulmonary picture after 30 years? a case report and review of the literature
No full textBackground: Alpha-1 antitrypsin, also known as alpha1 proteinase inhibitor, is a protein 90% synthesized by hepatocytes. Alpha-1 antitrypsin deficiency should be suspected if patients have unexplained emphysema or liver disease in the absence of others recognized causes. The diagnosis is based on tests that measure the amount of the enzyme in the blood and confirm by molecular analysis. Case presentation: We present the case of a man of Caucasian ethnicity, who started experiencing difficulty in breathing 20 years after liver transplantation. After about 30 years since transplantation, an intermediate alpha-1 antitrypsin deficiency is diagnosed with evidence of air trapping, pulmonary emphysema and bronchiectasis. Conclusion: The presence of a Z-variant synthesized from the donor liver may have contribute to the onset of respiratory disease
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