1,721,015 research outputs found
Continuum description of flow-like landslide dynamics
No full textLandslide run-out is a complex phenomenon, much more difficult to simulate by models than flow of fluids. The main complicating aspects concern that landslide material is often heterogeneous and its characteristics may change during the landslide movement due to drainage, hydraulic interaction between fluid and grains, comminution of grains or mixing with surface water or partly or fully liquefied superficial material entrained from the path.
The continuum mechanical theory, treating the heterogeneous and multiphase moving mass as a continuum, has emerged in the last years as a useful tool for describing the evolving geometry and the velocity distribution of a mass flowing down a surface. A hypothetical material, “equivalent fluid”, whose rheology is controlled by a small number of parameters is, in fact, introduced to represent the bulk behaviour of a landslide.
After a brief introduction on landslide characteristics and dynamics, new advances in the continuum mechanical description of flow-like landslides are discussed in dedicated sections. Each section deals with one of the main aspects that characterize the physical behaviour of a landslide and presents the simplifying, but nevertheless realistic, assumptions made to streamline their mathematical formulation.
The mathematical formulation is then implemented in a numerical code (RASH3D) to test the capability of each mathematical assumption in allowing the reproduction of real phenomena dynamics. Results of numerical simulations of laboratory tests and real events are discussed in this chapter to this aim
Effetti della reologia sull'analisi della propagazione di flussi di detrito
No full textIncontro annuale dei ricecatori in Ingegneria Geotecnica (IARG
Assessing potential debris flow runout: a comparison of two simulation models
No full textIn the present paper some of the problems related to the application of the continuum mechanics modelling to debris flow runout simulation are discussed.</br> Particularly, a procedure is proposed to face the uncertainties in the choice of a numerical code and in the setting of rheological parameter values that arise when the prediction of a debris flow propagation is required.</br> In this frame, the two codes RASH3D and FLO2D are used to numerically analyse the propagation of potential debris flows affecting two study sites in Southern Italy.</br> For these two study sites, a lack in information prevents that the rheological parameters can be obtained from the back analysis of similar well documented debris flow events in the area. As a prediction of the possible runout area is however required by decision makers, an alternative approach based on the analysis of the alluvial fans existing at the toe of the two studied basins is proposed to calibrate rheological parameters on the safe side.</br> From the comparison of the results obtained with RASH3D (where a Voellmy and a Quadratic rheologies are implemented) and FLO2D (where a Quadratic rheology is implemented) it emerges that, for the two examined cases, numerical analyses carried out with RASH3D assuming a Voellmy rheology can be considered on the safe side respect to those carried out with a Quadratic rheology
Comparison of depth-averaged and 3D models for dense granular flows
Full text linkDebris flows are one of the major threats to mountain communities. They consist of the downslope flow of fine and coarse material, saturated with water, along channelized paths. Due to their high velocity and unpredictability, the evacuation of hit areas may be difficult to execute. To avoid casualties and economic losses, mitigation structures, like filter barriers, are therefore usually adopted. Their primary task is to reduce the flow energy and to retain larger boulders. However, considerable room to improve the design of these structures still exists. In particular, gaining a better understanding of debris flows dynamics is a necessary step to improve the design of barriers. Numerical modelling can contribute to its understanding, and in an effective simulation of the flowing mass dynamics and impact against mitigation barriers. In this frame, the continuum-based Depth-Averaged Modelling (DAM) has been widely used since the 90s. In spite of the good results of this approach, together with the low computational time, the averaging procedure of velocity and pressure along the flow depth causes the loss of crucial information, which is important for correctly simulating the interaction with mitigation structures. A full 3D modelling can overcome this shortcoming by allowing a more complete flow representation, and a more accurate computation of impact forces. However, since debris flow may run for long distances, 3D models would require a large computational time. In this work we aim to study both the shortcomings and the advantages of the DAMs and 3D models. In particular, The DAM model used is DAN-W, while the 3D model is based on the lattice-Boltzmann method. To compare the results from numerical modelling, we use the experimental work performed by Moriguchi et al. (2009) in which a mass of dry sand flows on a steep chute
The force exerted by granular flows on slit dams
No full textBoulders often accumulate at the fronts of fast-flowing steep creek hazards. To trap these boulders, slit dams are commonly installed along steep creeks. An outstanding challenge when designing such dams lies in estimating the load exerted by a cluster of boulders: Clusters may exhibit discrete or continuum loading behavior, depending on their size. In this study, a physical flume test was carried out and the obtained results were used to calibrate a discrete element method (DEM) model. The DEM was then used to carry out a parametric study as a function of grain size, slit width and the channel slope. Results reveal that for continuum-like flows, the pressure near the slit of a slit dam can be almost double than elsewhere on the slit dam, as quantified using a newly proposed dimensionless ratio. For discrete flows, impact forces near the slit are more than double than elsewhere, thus representing a critical case for slit dam design. The concentration of forces near the slit necessitates designing for loads 2–3 times that of the rest of the slit dam to avoid wearing. (If wearing occurs, the slit width will increase, along with the volume of discharge, a potentially catastrophic scenario.) Furthermore, two dimensionless weighting coefficients that distinguish pressure from continuum-like flows and discrete impacts are proposed and evaluated. These coefficients can be incorporated into existing analytic expressions used by engineers
Post-wildfire debris flow in the Northwestern Italian Alps: description and numerical analysis of the June 2018 Bussoleno event
Full text linkOn June 7, 2018, a mud-debris flow occurred in the Comba delle Foglie basin, Susa Valley, Northwestern Italy. The event followed an unusually wet winter and spring with high cumulative rainfall, though no intense rainfall was recorded immediately prior to the flow. Approximately 20,000 m3 of sediments and woody debris were transported to an urbanized alluvial fan, causing severe damage, including the destruction of two residential buildings and widespread flooding. Key predisposing factors include extensive wildfires in Autumn 2017, which are atypical for this region characterized by an alpine climate. Following the event, significant mitigation measures were implemented. This study presents an analysis of the event, integrating data on fire damage, rainfall distribution, flow runout, and deposit thickness from post-event surveys. A numerical back-analysis of the flow dynamics is conducted using two approaches to define the triggering area. The simplified triggering approach applies a method frequently used in the literature, simulating the runout of a concentrated mass to evaluate the flow’s rheology. Two rheological laws are tested by comparing simulated flow depths and path with field data. The susceptibility-based triggering approach incorporates a preliminary susceptibility analysis, integrating fire severity mapping and literature findings to account for wildfire-induced impacts on soil stability. A comparison of
the simulations shows that the susceptibility-based analysis better reproduces the flow path, enhancing back-analysis accuracy. However, the simplified approach remains a reliable tool for the case study. Finally, the effectiveness of the implemented mitigation measures is assessed through numerical simulations, providing
insights into the settlement’s potential response to future debris flow events
Experimental study for the design of flexible barriers under debris flow impact
No full textDebris flows are wide spread phenomena in mountain areas and due to their high velocity and kinetic energy, are very destructive processes in terms of human life and structures. Several studies have been dedicated to both triggering and propagation phases of a mass movement but there is still a lack of knowledge about the behavior of the flow during its impact against an obstacle. In particular, the crucial point is the definition of the impact action, fundamental to design protection barriers, that depends on the flow nature and propagation characteristics (velocity and thickness). These entities are difficult to be determined by means of experimental measurement and consequently several empirical and theoretical relations were proposed in literature. Laboratory tests on scaled channel are also available but they are often affected by the limitation of the scale effects. The aim of this paper is to analyze in detail the impact of a debris flow against an obstacle and present a new method to design these protection structures: this method combines the numerical method DAN and the Brighenti's method in order to evaluate the flow characteristics and quantify the action applied to the barrier. Laboratory tests have allowed for model calibration and for the validation of the hypothesis about the nature of the impact
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