Field observations of the June 30, 2001 debris flow at Acquabona (Dolomites, Italy)

On June 30, 2001, a debris flow occurred in the Acquabona Creek, a small catchment of the Eastern Dolomites, Italy. This debris flow originated shortly after an intense rainstorm, characterised by a peak intensity of 8.6 mm per 10 min; it transported a total volume of 30,000 m3, consisting of poorly sorted gravely sand with boulders up to 3 m in diameter. The sediment erosion yield rate reached as high as 20 m3/m. In order to verify the accuracy of the field measurements, the total volume of debris deposits was calculated using three different topographic measurement techniques: 3D laser scanning, terrestrial stereo-photogrammetry survey and total topographic station survey. Data collected so far show that no debris flow has occurred at Acquabona with a rainfall intensity lower than 4.6 mm per10 min. Channel cross section measurements indicate that debris flow velocity ranges from 2.0 to 7.2 m/s along the lower flow channel and peak discharge ranges between 22 and 300 m3/s. Field estimates of the rheological properties indicate a yield strength ranging from 2,088 to 5,313 Pa and Bingham viscosity between 70 and 337 Pa.s. It is not still possible to identify a rainfall intensity and amount threshold for debris flow triggering, but the data so far collected emphasise that debris flows do not occur with a rainfall intensity lower than 4.6 mm per 10 min

A new approach to the measurement of a landslide displacement field by using terrestrial laser scanner

Abstract EGU06-A-0825

Characterization of landslide ground surface kinematics from terrestrial laser scanning and strain field computation

Assessment and mitigation of the risk induced by landslide activation need an appropriate phenomenon investigation, to obtain useful information about the failure processes. The first step is the complete kinematics characterization of the landslide ground surface, by evaluating the involved displacement and deformation patterns. A dense displacement field can be obtained from comparison of a series of multi-temporal observations performed by means of terrestrial laser scanning. Subsequently, the strain field can be computed from displacement vectors. In this paper, a modified least square technique is employed to compute the strain on the nodes of a regular grid (2D approach) or on the points of a digital terrain model (3D approach). Such a computation takes into account the displacements, their spatial distribution, as well as the measurement and modelling errors. A scale factor is introduced in order to emphasize the contributions of the experimental points on the basis of their distance from each computation point, and to recognize possible scale-depending behaviours. This method has been implemented in Matlab and applied on two landslides located in the northeastern Italian Alps (Lamosano and Perarolo di Cadore). The experiments show that different kinematics can be recognized, and the presence and influence of eventual discontinuities can be revealed

Mesure des champs de déplacement de surface et modélisation numérique des glissements de terrain

Trois glissements de terrain, La Valette et La Clapière (France) et S. Andrea (Italie), ont été étudiés à l'aide d'études des mouvements de surface et des modélisations aux différences finies. Sur les sites de La Valette et La Clapière, les techniques de l'interférométrie SAR et du GPS ont permis d'obtenir une meilleure compréhension de la cinématique et de l'évolution des mouvements de surface et de distinguer, délimiter et décrire des secteurs à différente activité. L'étude topographique menée sur le site de S. Andrea a montré une activité de la portion centrale et occidentale du versant. Les observations de terrain conduites sur le versant ont permis la réalisation d'un modèle géologique et géotechnique de la zone en mouvement, qui a fait objet de la modélisation aux différences finies en 2D et 3D. Cette technique a permis de calculer l'état de contrainte du versant, de proposer la position d'une ou plus surfaces de rupture potentielles et de proposer des possibles interventionsLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Comparison of numerical models of two debris flows in the Cortina d'Ampezzo area, Dolomites, Italy

The accurate prediction of runout distances, velocities and the knowledge of flow rheology can reduce the casualties and property damage produced by debris flows, providing a means to delineate hazard areas, to estimate hazard intensities for input into risk studies and to provide parameters for the design of protective measures. The application of most of models that describe the propagation and deposition of debris flow requires detailed topography, rheological and hydrological data that are not always available for the debris-flow hazard delineation and estimation. In the Cortina d\u2019Ampezzo area, Eastern Dolomites, Italy, most of the slope instabilities are represented by debris flows; 325 debris-flow prone watersheds have been mapped in the geomorphological hazard map of this area. We compared the results of simulations of two well-documented debris flows in the Cortina d\u2019Ampezzo area, carried on with two different single-phase, non-Newtonian models, the one-dimensional DAN-W and the twodimensional FLO-2D, to test the possibility to simulate the dynamic behaviour of a debris flow with a model using a limited range of input parameters. FLO-2D model creates a more accurate representation of the hazard area in terms of flooded area, but the results in terms of runout distances and deposits thickness are similar to DAN-Wresults. Using DAN-W, the most appropriate rheology to describe the debrisflow behaviour is the Voellmy model. When detailed topographical, rheological and hydrological data are not available, DAN-W, which requires less detailed data, is a valuable tool to predict debris-flow hazard. Parameters obtained through back-analysis with both models can be applied to predict hazard in other areas characterized by similar geology, morphology and climate

Influence of the antiformal setting on the kinematics of a large mass movement: the Passo Vallaccia, eastern Italian Alps

The article examines the influence of antiformal settings on the evolution of alpine slopes using 2D numerical modelling. The northern slope of the Upper Vizze Valley, which follows a huge antiform involving meta-granitic and meta-sedimentary rocks, is affected by a complex gravitational phenomenon mainly controlled by the attitude of the foliation. A preliminary geological model based on field surveys was refined using the results of 2D distinct element numerical modelling. In the crown area, the sub-horizontal meta-sedimentary sequence at the fold hinge is cut by sharp planes, whilst in the middle zone the sequence was passively dragged downwards and finally, in the lowest part of the slope, corresponding to the steeply dipping antiformal flank, the deformation propagated across the entire meta-sedimentary succession through strain partitioning along multiple shear surfaces

Failure mechanisms and runout behaviour of three rock avalanches in thye North-Eastern Italian Alps

The nature of the physical processes that trigger rockslope insatbility is, today, understood even if with some difficulties and simplifying hypothesis, but the striking mobility of the flow of these rock masses remains in a large part inexplicable. Three major rock avalanches in the Italian alps have been studied focusing in particular on aspects relating to the fragmentation and deposition processes. Studies have focused on grain size distribution of samples taken at different distances and elevation and on the morphology of the ground surface of the deposits. Image analysis technique was useful to complete the cumulative grain size curves to include larger particles. In none of the three cases the significant parameters of the grain size distribution and of the particles moprphology have shown any relationships with the distance from the center of the failed mass and with the height of the taken sample on the base of the deposits. The roundness of particles is practically the same within the whole deposit and even between different depositsfor which travel distances and thicknesses are different. The morphology of the three deposits gave some information on the dynamics of the phenomenon and, in particular, on the progressive thinning of the moving debris

Studio sulle caratteristiche delle cave in sotterraneo

(in italiano