1,400 research outputs found
Monitoring Of Temperature-Induced Deformations in High Mountain Huts
No full textGlobal warming is affecting a lot ofhuman activities and has a relevant environmental impact. This is particularly evidentin the Alps, where the recorded temperature increases are larger than average. This trend has direct consequences onthe stability of high mountain slopes, as it provokes the upward receding of permafrost and triggers a series of rockfall events. Although it is difficult to pinpoint the direct cause-effectrelationship for any recorded event, two general facts emerge: failures are becoming more and more frequent, especially during particularly hot summer seasons; failures tend to concentrate within the altitude range affected by permafrost receding.In this paper,we discuss the structuralmonitoring at Capanna Margherita hut (Punta Gnifetti 4554m a.s.l., Monte Rosa massif), which is the highest mountain hut in the Alps and Europe in general. Geomechanicalmonitoring was activated there in 2023 and it is now complemented by the installation of sensors onthe hut structurein 2024. Afull set of data is continuously being recorded, including inclinometric, thermometric and accelerometric data.The paperanalysisis based on the data recorded by thesensors and the air temperature at Capanna Margherita hut, includingthe relationship between the temperatures and displacements, and the dynamic characteristics of structural vibrations
Interparticle forces distribution in granular materials: link with the macroscopic behaviour
No full textThis paper addresses the modelling of the incremental behaviour of an idealized granular material and its link with the distribution of contact forces within the representative volume. Based on the results obtained from a series of numerical DEM experiments, a discussion of the di!erent operations used in a micro mechanical modelling framework is proposed. First, the relevance of the usual description of the contact forces distribution through its average value for a given contact orientation is evaluated. Next, this description is implemented in a complete homogenization process. The derived stress}strain relationship acceptably predicts the anisotropic elastic properties of the material provided that the particles do not rotate
but fails to if this constraint is removed. Therefore, in the last section, a more re"ned description of the contact forces distribution is invoked, considering the actual scatter from the average values through the standard deviation
DEM Modelling of Ice Filled Rock Joints
No full textThe research we present in this paper is part of a wider project about the modelling of climate change effects on the degradation of permafrost, with particular attention for the stability of rock masses. The presence of ice and/or mixtures of ice and granular materials in rock joints has a big impact on the shear resistance of joints and on the evolution of joint persistence. In previous research we modelled the mechanical behavior of ice and frozen soils with a Distinct Element model and compared the evolution of the resistance with ice content with experimental data available in the literature. In this paper, we are focusing on rock joints and we are modelling both fill material (ice and frozen soil mixtures) and rock as collections of Distinct Elements, taking advantage of the previous experience in terms of calibration of the parameters. In particular, in this preliminary study, we will focus on the shear resistance of joints as a function of the composition of the fill material. The purpose of this research is to study the mechanical behavior of joints and derive the corresponding force-displacement relationship to be assigned to the interfaces between blocks in a full scale model of rock masses
DEM Simulation of Frozen Granular Soils with High Ice Content
No full textHigh volumetric ice content is one of the structural features of alpine permafrost. The mechanical properties of pure ice are very different from those of dry soil and as a consequence the mechanical properties of frozen soil are highly dependent on the ice content, as highlighted by triaxial experiments available in the literature. On the basis of existing data from experiments under different stress paths (axis-symmetric compression and extension), this paper presents a frozen soil model by using the particle-based discrete element method (DEM). In the model two groups of elements are used for representing soil particles and ice, and two separate sets of micromechanical parameters are calibrated and assigned to each group. Elements from the two groups are then mixed in different proportions in order to simulate the effect of ice content. A series of triaxial compression simulations are then performed and analysed
Micromechanical modelling of erosion due to evaporation in a partially wet granular slope
No full textSmall quantities of water in a granular slope increase the overall stability and justify the large slope angle which is sometime observable in nature. However, the evaporation usually changes the water content of soil, especially in very shallow layers, leading to a soil strength reduction and the trigger of erosion processes. This work presents some numerical tests simulating a small slope physical model constituted of monosized glass ballotini in a pendular state. After a brief review of the different theories describing the capillary bridge which forms between two spheres and its effects on inter-particle forces, this paper deals with the implementation of the minimum energy approach within a discrete element model (DEM). Some numerical triaxial tests with different water contents and confinement stresses were performed: the analyses permitted to emphasize the shear strength increase occurring at low water content. Moreover, moving from the observations performed in the physical model, a law relating the evaporation rate with depth and air–water interface was also included in the DEM. Finally, the improved DEM was successfully adopted in the simulation of the erosion process occurring in the physical model: it very well captures the formation of a talus slope profile, typical of the long-term evolution of granular slopes. The monitoring of soil displacements and suction distribution during the numerical test also allows for the evaluation of erosion mechanisms: for instance, both in experimental and numerical tests, it was observed a rigid displacement at the slope toe after the initial phase of shallow erosionSCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe
Analisi dell’installazione di pali a spostamento di terreno con il metodo agli elementi discreti
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Dry granular masses impacting on rigid obstacles: numerical analysis and theoretical modelling
No full textThe assessment of the time evolution of the impact force exerted by dry flowing masses on rigid obstacles is mandatory for the dynamic design of sheltering structures and the evaluation of the vulnerability of existing structures. In this paper, the results of an extensive numerical campaign performed by employing a discrete element method (DEM) code are presented and the role of different geometrical factors (flow length, height and front inclination) and state parameters (porosity and velocity) on the impact force–time evolution is investigated. The impact process is studied to correlate local information with the macroscopic response and a physically based force–time function, generalising the formula already introduced by the authors for the assessment of maximum impact force, in which each parameter is correlated with the previously mentioned factors, is proposed
Use of an up-scaled DEM model for analysing the behaviour of a shallow foundation on a model slope
No full textUse of an up-scaled DEM model for analysing the behaviour of a shallow foundation on a model slope.
No full textThis paper presents a methodological approach for the DEM modelling of geotechnical problems. The approach is based on quite general principles, which are illustrated with reference to a specific problem, i.e. the reproduction of a physical model of a foundation on a sandy slope. The approach mainly consists in the reproduction of the involved soil using a small, but statistically representative, assembly of spheres characterized by the same porosity and a slightly simplified grain-size curve. The DEM parameters are calibrated on the base of some standard compression tests on the same material utilised in the physical model. The thus calibrated DEM model is finally utilised to reproduce the tests on the model foundation, but, to limit the computational effort in this latter phase, an up-scaled grain-size curve is adopted and the corresponding DEM parameters are determined using the
scaling rules provided with the approach. The performance of the numerical model in predicting the experiments is assessed by comparing both global results (foundation load--settlement curves) and local measurements (strain field). Moreover, the DEM model is finally used to test the foundation behaviour in some different loading conditions that could not be investigated in the laboratory
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