In active landslides, the prediction of acceleration of movement is a crucial issue for the design and performance of warning systems. The landslide of Vallcebre in the Eastern Pyreenes, Spain, has been monitored since 1996 and data on rainfall, groundwater levels and ground displacements are measured on a regular basis. Displacements observed in borehole wire extensometers have shown an immediate response of the landslide to rainfall episodes. This rapid response is likely due to the presence of preferential drainage ways. The occurrence of nearly constant rates of displacement in coincidence with steady groundwater levels suggests the presence of viscous forces developed during the movement. An attempt to predict both landslide displacements and velocities was performed at Vallcebre by solving the momentum equation in which a viscous term (Bingham and power law) was added. Results show that, using similar rheological parameters for the entire landslide, computed displacements reproduce quite accurately the displacements observed at three selected wire extensometers. These results indicate that prediction of displacements from groundwater level changes is feasible.
The paper presents an analysis of the desiccation process in mining materials, based on physical laws. Due to the process complexity, most of the previous approaches used have an empirical basis. In this case, however, a formulation using coupled hydromechanical equations has been considered. To show the capabilities of the theoretical framework, several laboratory tests were performed, and afterwards a numerical simulation of the measured variables was attempted. The material tested was a metallurgical waste in tailings form and it was exposed to atmospheric desiccation. Further cracking will eventually change its properties, and this may have an environmental impact. Some of the experiments were devoted to material characterization, including the water retention curve, the hydraulic conductivity, and the tensile strength. In addition, laboratory drying tests open to the atmosphere or in hermetically closed containers were also performed. The numerical analyses carried out attempted to simulate some of these tests. One of the main outcomes of the analyses was the prediction of the time and the location of crack initiation. Finally, it should be pointed out that good agreement between the experiments and numerical simulations indicates that the formulation is taking into account the fundamental mechanisms involved in the desiccation process
Negative pore pressures existing in semi-saturated conditions provide a substantial ‘cohesion’ of the soil. This cohesion is of importance in the dynamic response of embankments and dams. The paper extends the formulation presented in part I to problems of semi-saturated behaviour with the assumption of free air ingress. An approximate reconstruction of the failure of the lower San Fernando dam during the 1971 earthquake is presented.
Results of an experimental study on the formation of crack patterns during drying of a soil paste are presented. The objective is to ascertain whether fracture mechanics plays a significant role in explaining the process of formation and propagation of cracks during drying of soils due to changes in environmental conditions such as temperature and humidity. The experiments consist of five geometrically similar rectangular specimens in two series of different thicknesses, subjected to drying conditions in an environment-controlled laboratory. Cracking initiates shortly before the soil reaches a near-solid quasi-brittle consistency. Although crack initiation can be explained by classical soil mechanics effective stress theory, crack development and propagation appear to be energy-driven. The results prove that cracking stress does depend on the size of the specimen and suggest that fracture mechanics might be applicable to soil cracking, at least in the context of the present research. Fracture toughness of the soil used was determined using compact tension tests at different water contents. Its tensile strength was also determined by a direct method for two natural specific weights (bulk density) and two dry specific weights with different water contents.Résumé : Cet article présente les résultats d'une étude expérimentale sur la formation de fissures durant l'assèchement d'une pâte de sol. L'objectif est de vérifier si la mécanique des fractures joue un rôle significatif dans l'explication des processus de formation et de propagation de fissures lorsqu'un sol sèche en raison de changements dans les conditions environnementales, comme la température et l'humidité. L'expérimentation consistait à soumettre cinq échantillons de géométrie similaire et ayant deux séries d'épaisseurs différentes à des conditions d'assèchement dans un environnement contrôlé de laboratoire. Les fissures sont initiées tout juste avant que le sol atteigne une consistance presque solide et quasi-fragile. Cependant, même si l'initiation des fissures peut être expliquée par la théorie des contraintes effectives classiques de la mécanique des sols, le développement et la propagation des fissures semblent être contrôlés par l'énergie. Les résultats prouvent que la contrainte de fissure dépend de la taille de l'échantillon, et suggèrent que la mécanique des fractures peut être applicable aux fissures dans les sols, du moins dans le contexte de cette étude. La résistance aux fractures du sol utilisé a été déterminée à l'aide d'essais en tension compacts à différentes teneurs en eau. Sa résistance en tension a aussi été déter-minée par une méthode directe pour deux poids spécifiques naturels (densité globale) ainsi que pour deux poids spécifiques secs à différentes teneurs en eau.Mots-clés : fissure dans le sol, dessiccation, effet de taille, résistance en tension, résistance aux fractures, mécanique des fractures.[Traduit par la Rédaction]
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