Slider-Block Friction Model for Landslides: Application to Vaiont and La Clapiere Landslides

Accelerating displacements preceding some catastrophic landslides have been found empirically to follow a time-to-failure power law, corresponding to a finite-time singularity of the velocity $v \sim 1/(t_c-t)$ [{\it Voight}, 1988]. Here, we provide a physical basis for this phenomenological law based on a slider-block model using a state and velocity dependent friction law established in the laboratory and used to model earthquake friction. This physical model accounts for and generalizes Voight's observation: depending on the ratio $B/A$ of two parameters of the rate and state friction law and on the initial frictional state of the sliding surfaces characterized by a reduced parameter $x_i$, four possible regimes are found. Two regimes can account for an acceleration of the displacement. We use the slider-block friction model to analyze quantitatively the displacement and velocity data preceding two landslides, Vaiont and La Clapi\`ere. The Vaiont landslide was the catastrophic culmination of an accelerated slope velocity. La Clapi\`ere landslide was characterized by a peak of slope acceleration that followed decades of ongoing accelerating displacements, succeeded by a restabilizing phase. Our inversion of the slider-block model on these data sets shows good fits and suggest to classify the Vaiont (respectively La Clapi\`ere) landslide as belonging to the velocity weakening unstable (respectively strengthening stable) sliding regime.Comment: shortened by focusing of the frictional model, Latex document with AGU style file of 14 pages + 11 figures (1 jpeg photo of figure 6 given separately) + 1 tabl

Quantifying the interplay between environmental and social effects on aggregated-fish dynamics

Demonstrating and quantifying the respective roles of social interactions and external stimuli governing fish dynamics is key to understanding fish spatial distribution. If seminal studies have contributed to our understanding of fish spatial organization in schools, little experimental information is available on fish in their natural environment, where aggregations often occur in the presence of spatial heterogeneities. Here, we applied novel modeling approaches coupled to accurate acoustic tracking for studying the dynamics of a group of gregarious fish in a heterogeneous environment. To this purpose, we acoustically tracked with submeter resolution the positions of twelve small pelagic fish (Selar crumenophthalmus) in the presence of an anchored floating object, constituting a point of attraction for several fish species. We constructed a field-based model for aggregated-fish dynamics, deriving effective interactions for both social and external stimuli from experiments. We tuned the model parameters that best fit the experimental data and quantified the importance of social interactions in the aggregation, providing an explanation for the spatial structure of fish aggregations found around floating objects. Our results can be generalized to other gregarious species and contexts as long as it is possible to observe the fine-scale movements of a subset of individuals.Comment: 10 pages, 5 figures and 4 supplementary figure

Numerical simulation of entangled materials mechanical properties

A general approach to simulate the mechanical behaviour of entangled materials submitted to large deformations is described in this paper. The main part of this approach is the automatic creation of contact elements, with appropriate constitutive laws, to take into account the interactions between fibres. The construction of these elements at each increment, is based on the determination of intermediate geometries in each region where two parts of beams are sufficiently close to be likely to enter into contact. Numerical tests simulating a 90% compression of nine randomly generated samples of entangled materials are given. They allow the identification of power laws to represent the evolutions of the compressive load and of the number of contact

Approach to Heterogeneous Strain Distribution in Cable-In-Conduit Conductors Through Finite Element Simulation

International audienceThe ITER Cable-In-Conduit Conductors are submitted to high thermal and electromagnetic cyclic loadings responsible for conductivity loss in the strain-sensitive Nb3Sn strands. The complex mechanical phenomena occurring at the local scale of the strands make the final performances of the CICC difficult to predict from single-strand properties. In order to assess the amplitudes of the local strains that drive the conductor electrical behavior, a nonlinear finite element simulation code is used. The successive stages of the conductors' service life, from the forming of the cable to its thermal cool down and Lorentz force loading, are simulated. Each strand is individually modeled along with the great number of contacts-friction interactions between the strands. This paper presents the simulation results obtained for 144 strand cables of two different designs. It is shown that the various loadings result in a heterogeneous distribution of strains along and across the strands with occurrence of extreme tensions and compressions. The use of simulation would eventually help to better characterize the influence of conductor design parameters

Numerical Simulation of the Mechanical Behavior of ITER Cable-In-Conduit Conductors

International audienceThe unexpected degradations of current carrying capacity of Cable-In-Conduit Conductors are attributed to be mechanical in origin Nb3Sn. As a result, the prediction of conductor's performances asks for the assessment of the local strain state of the Nb3Sn superconducting strands inside cables. For this purpose, a finite element modeling, specially developed for the simulation of cable mechanics, is presented in this paper. The presented mechanical model allows simulating the conductors' service life from manufacturing to operating conditions by describing the evolution of strains and stresses within each individual strand. The distributions of axial strains within strands, obtained from simulation results of both thermal and Lorentz loadings, could help characterize the influence of design parameters