Fuzzy modelling of powder snow avalanches

This paper examines powder snow avalanches by introducing a predetermined degree of variation, or fuzziness, in model parameters. Given a value of vagueness in the parameters, fuzzy set theory makes it possible to evaluate the vagueness in the results. The use of a more complex stochastic analysis can be avoided. Six parameters of the model are taken to be affected by a certain amount of uncertainty; the response of the numerical model is calculated by solving the fuzzy equations. In this way, it is possible to evaluate how the results are affected by a given change in the model parameters. The paper first presents a well-known avalanche model and its solution considering the influence of friction. A brief introduction of the fuzzy set is given with regard to the avalanche model mentioned. Later, the fuzzy solution of the model in terms of velocity and average pressure is calculated for three different levels of imprecision in the data. At the end, the results are presented and commented

Lifetime evaluation of concrete structures under sustained post-peak loading

Experimental tests on crack propagation in concrete under constant post-peak loading are simulated using the finite element method and the cohesive crack model, in both Mode I and Mixed-mode conditions. The time-dependent behaviour of concrete in the process zone is due to the interaction and growth of microcracks, a phenomenon which, for high constant load levels, turns out to be predominant over linear viscoelastic creep in the bulk material. In mechanical systems based on this type of material behaviour (creep and strain-softening taking place simultaneously), the initial value problem is non-parabolic, i.e., the error at one time level is affected by the accumulation of errors introduced at earlier time levels. Despite these difficulties, the scatter in numerical failure lifetime vs. load level turns out to be negligible in Mode I conditions and practically acceptable in Mixed-mode conditions. Therefore the time-dependent behaviour of the process zone can be inferred solely from the results of direct tensile tests

The cohesive frictional crack model applied to the analysis of the dam-foundation joint

The mechanical behaviour of dam-foundation joints plays a key role in concrete dam engineering since it is the weakest part of the structure and therefore the evolutionary crack process occurring along this joint determines the global load-bearing capacity. The reference volume involved in the above mentioned process is so large that it cannot be tested in a laboratory: structural analysis has to be carried on by numerical modelling. The use of the asymptotic expansions proposed by Karihaloo and Xiao at the tip of a crack with normal cohesion and Coulomb friction can overcome the numerical difficulties that appear in large scale problems when the Newton-Raphson procedure is applied to a set of equilibrium equations based on ordinary shape functions (Standard Finite Element Method). In this way it is possible to analyze problems with friction and crack propagation under the constant load induced by hydro-mechanical coupling. For each position of the fictitious crack tip, the condition K1=K2=0 allows us to obtain the external load level and the tangential stress at the tip. If the joint tangential strength is larger than the value obtained, the solution is acceptable, because the tensile strength is assumed negligible and the condition K1=0 is sufficient to cause the crack growth. Otherwise, the load level obtained can be considered as an overestimation of the critical value and a special form of contact problem has to be solved along the fictitious process zone. For the boundary condition analyzed (ICOLD benchmark on gravity dam model), after an initial increasing phase, the water lag remains almost constant and the maximum value of load carrying capacity is achieved when the water lag reaches its constant valu

Numerical modelling of ground-tunnel support interaction using bedded-beam-spring model with fuzzy parameters

The study of the ground-tunnel interaction by introducing a predetermined degree of variation (fuzziness) in some parameters of the chosen model is presented and discussed. This research comes from the consideration that tunnel model parameters and geometry are usually affected by a degree of uncertainty, mainly due to construction imprecision and the great variability of rock mass properties. The research has been developed by using the fuzzy set theory assuming that three model parameters are affected by a certain amount of uncertainty (defined by the so-called membership functions). The response of the numerical model is calculated by solving the fuzzy equations for different shapes of the membership functions. In order to investigate the effects of some model parameters, and to provide a simple procedure and tool for the designers, a study on the effect of tunnel boundary conditions, based on a fuzzy model, has been carried out using a simple but well known and widely used design method such as the bedded-beam-spring mode

Fracture Mechanics Characterization of an AnisotropicGeomaterial

Argillites are considered worldwide as potential host rock for high level radioactive waste given the low permeability and strong adsorption potential. However, the excavation of the galleries of a repository would produce a disturbed zone around the boundaries rich of new fractures which may enhance the conductivity of the rock along the gallery axis. Several mine-by experiments have been performed in underground rock labs to investi- gate the features of the disturbed zone. In Mont Terri URL (Kanton Jura, Switzerland) the EZ-B experiment was specifically conceived for the measurement of excavation induced fractures around a small chamber. The host rock of the URL is a particularly compact and resistant argillite, known as the Opalinus Clay (OPA) excavated and OPA samples were subjected to fracture mechanics tests at the rock mechanics lab of IGAG-CNR in Torino, Italy. The tests aimed at the understanding aspects of the fracturing process occurring in OPA of Mont Terri, which may be considered a transversely isotropic geomaterial, whose planes of isotropy coincide with the beddin

Hacking the Higher Education: Experiences from EduHack Course

At present e-learning courses have increased their importance but only a few universities use them, so it is crucial to explore the best ways of using this method for education. This paper is the result of a collaboration among some university teachers that recently have taken part to the EduHack course. The article aims to share their experience with a wider scientific community in order to promote a reflection on e-learning tools and methods specifically reserved for university teaching. This study highlights the structure and the organization of the EduHack course and presents Drag&Fly, the project idea developed by the authors during the collaborative part of the course, called EduHackathon. Some proposals to enhance the experience of participation are discussed by answering the following questions: What feelings did the EduHack course convey? What were its main strengths? What could be improved? Using concepts and categories of analysis widespread in the pragmatic theoretical tradition and adopting a qualitative analysis method based on the reconstruction of the experience through the participants’ observation, the Authors will analyze the learning generated by participating in the EduHack course. Its transformative potential will be investigated, as well as the possibility of changing the teachers’ approach to the design and implementation of a higher educational e-learning course

Hacking Higher Education: Rethinking the EduHack Course

The paper presents a report that discuss the experience of participation of the authors in the EduHack, an online course designed to train university teachers in the use of digital techniques and learning strategies. This study highlights two issues of great interest in pandemic times. The first one is the structure and the organization of the EduHack course with some suggestions related to its improvement; the second one is Drag&Fly, the project idea of an eLearning web platform developed by the authors during the collaborative part of the course. The experience of participation to EduHack course has been analyzed by authors using concepts and categories of analysis widespread in thecpragmatic theoretical tradition, enhancing the possibility of changing the teachers’ approach to thedesign and the implementation of a higher education e-learning course

Towards a general constitutive model for snow

Reproducing the mechanical behaviour of snow is a challenging task for many different application fields (e.g., Civil and Environmental Engineering, Physics, etc.) and can be useful to study many topics, such as: the stability of mountain snowpacks, the safety of structures and infrastructures in cold environments, the social and physical risk for people and goods in snow covered areas. The available constitutive models for snow generally use the elasto-plastic (EP) theory to reproduce different and complex items of this peculiar material with reference to both laboratory and on-site conditions. Nevertheless, these models are often related to some specific types of snow (i.e., rounded grains, faceted crystals, etc.) and cannot be used for general purposes. Moreover, many models do not consider viscosity, rate-sensitivity, bonding effects, etc. In this work, we introduce the theoretical bases of our proposal for a new and improved constitutive model for snow. The model is based on the theory of visco-plasticity for finite element applications with an implicit integration scheme, and can reproduce both qualitatively and quantitatively the findings of some literature experimental data. For instance, promising results are obtained for the following tests: triaxial compression and relaxation, volumetric compression, and creep. Finally, we suggest possible improvements of the model to include important snow features not considered so far, such as: the collapse in compression of the weak layer (anticrack), the change in shape of snow grains, the ductile-to-brittle transition of the material, etc

Chemical-Physical Characterization of Stava Tailings Subjected to an Innovative Aging Technique

Tailing dams are realized to store the waste products resulting from the mining extraction processes. These complex geotechnical structures should be designed taking into account long-term stability and long-term properties of the deposited materials. Depending on the interactions between source mineralogy and local conditions, tailing wastes can undergo aging processes with chemical and physical modifications. Recently, in many countries tailing wastes are re-used as feedstock for cement and concrete, backfill or landscaping material, so if any, the long-term chemical and physical modifications could affect the hydro-mechanic response of tailings, resulting in relevant environmental and economic consequences. An increased interlocking of particles and oxidation, sometimes making previously safely held contaminants available and mobile, are recognized as common aging processes. Among the long-term aging processes, the natural ionizing radiation due to ultraviolet rays or cosmic rays can be considered. Moving from these reasons, this paper presents an innovative accelerated aging technique to simulate the natural ionizing radiation from the sun. Tailing fluorite ore samples collected form the collapsed Stava dams (Italy) were characterized in dry and wet conditions, before and after the gamma rays treatment. Stava silty tailings showed some physical modifications in terms of specific surface, size particle distribution and inner porosity of the particles, while they revealed a certain chemical stability