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This paper introduces a three-dimensional model for simulating dense-snow avalanches, based on the numerical method of cellular automata. This method allows one to study the complex behavior of the avalanche by dividing it into small elements, whose interaction is described by simple laws, obtaining a reduction of the computational power needed to perform a three-dimensional simulation. Similar models by several authors have been used to model rock avalanches, mud and lava flows, and debris avalanches. A peculiar aspect of avalanche dynamics, i.e., the mechanisms of erosion of the snowpack and deposition of material from the avalanche is taken into account in the model The capability of the proposed approach has been illustrated by modeling three documented avalanches that occurred in Susa Valley (Western Italian Alps). Despite the qualitative observations used for calibration, the proposed method is able to reproduce the correct three-dimensional avalanche path, using a digital terrain model, and the order of magnitude of the avalanche deposit volume. DOI: 10.1061/(ASCE)0887-381X(2007)21:4(121) CE Database subject headings: Avalanches; Snow; Numerical models; Disasters.

The aim of this work is to investigate the behavior of a 96-m-high gravity dam (the prototype) with a preexisting crack. For this purpose, four different gravity dam models were simulated through the cohesive crack model in mixed-mode conditions. Three of the models (1:40, 1:100, and 1:150 scale) were tested under equivalent dead-weight and hydraulic loads. To obtain correct dead-weight scale ratios, the laboratory tests were performed in an artificial gravity field produced by a system of additional vertical forces and by using a centrifuge. The initial notch in the upstream face served as the starting point of a crack that propagated toward the foundation during the loading process. The structural response and the crack trajectories were reproduced satisfactorily by the cohesive crack model. The behavior of the prototype is discussed on the basis of the behavior of the models.

Looking at the long-time behaviour of a dam, it is necessary to assume that the water can penetrate a possible crack washing away some components of the concrete. This type of corrosion reduces the tensile strength and fracture energy of the concrete compared to the same parameters measured during a short-time laboratory test. This phenomenon causes the so called sub-critical crack propagation. That is the reason why the International Commission of Large Dams recommends to neglect the tensile strength of the joint between the dam and the foundation, which is the weakest point of a gravity dam. In these conditions a shear displacement discontinuity starts growing in a point, called Fictitious Crack Tip (shortened FCT), which is still subjected to a compression stress. In order to manage this problem, in this paper the cohesive crack model is re-formulated with the focus on the shear stress component. In this context, the classical Newton-Raphson method fails to converge to an equilibrium state. Therefore the approach used is based on two stages: (a) a global one in which the FCT is moved ahead of one increment; (b) a local one in which the non-linear conditions occurring in the Fracture Process Zone are taken into account. This two-stage approach, which is known in the literature as a Large Time Increment method, is able to model three different mechanical regimes occurring during the crack propagation between a dam and the foundation rock. [ABSTRACT FROM AUTHOR]

Natural sintering in ice is a fundamental process determining mechanical properties of various ice forms. According to the literature, limited data are available about the complex subjects of snow sintering and bond formation. Here, through cold laboratory mechanical tests with a new shear apparatus we demonstrate time-dependent effects of isothermal sintering on interface strengthening at various normal pressures. Measurements showed that interfacial strength evolved rapidly, conforming to a power law (mean exponent ≈ 0.21); higher pressure corresponded to higher initial strength and sintering rates. Our findings are consistent with observations on homogeneous snow, provide unique records essential for slope stability models and indicate the significant importance of normal load on data interpretation. [ABSTRACT FROM AUTHOR]

The safety of cracked concrete dams is fundamentally affected by the mechanical behaviour of the material under cyclic loading conditions. In this case the crack can grow at a lower load level compared to the monotonic case. This phenomenon is called subcritical crack propagation and depends on the mechanical behaviour of the fracture process zone. To assess this phenomenon, a number of experimental tests, where the loading process is based on a first monotonic step (stopped before reaching the peak load), followed by a series of cyclic loading phases until collapse, are examined. The results of numerical analyses appear to be in good agreement with the experimental data obtained in the case of wedge splitting tests. [ABSTRACT FROM AUTHOR]

The paper analyses the interaction between strain-softening and time-dependent behaviour in the case of quasi-static fracture of concrete. A viscous element based on a fractional order rate law is coupled with a micromechanical model for the fracture process zone. This approach makes it possible to include a whole range of dissipative mechanisms in a single rheological element. Creep fracture in mode I conditions is analysed through the finite element method, the cohesive (or fictitious) crack model and a new space and time integration scheme. The comparison with creep tests executed on three-point bending conditions shows a good agreement. [Copyright &y& Elsevier]

The article presents a prototype of a new device for measuring the shear strength of snow specimens in situ. The resistance to sliding of a snow slab on a mountain slope is a key parameter in snow mechanics. The proposed apparatus acts as a sampler, to obtain a nearly undisturbed specimen, and as a shear box, similar to those used in the laboratory, with complete control of the test procedure. The main components of the device are a pneumatic system, for the application of normal and shear forces to the specimen, a real‐time controller for commanding and recording of the data, and a computer. The apparatus can be carried to the place of the experiments and operated by a team of two researchers. Calibration and preliminary tests are also described in the article. [ABSTRACT FROM AUTHOR]