Landslides — Cause and effect

SummaryLandslides can cause seismic disturbances; landslides can also result from seismic disturbances, and earthquake-induced slides have caused loss of life in many countries. Slides can cause disastrous flooding, particularly when landslide dams across streams are breached, and flooding may trigger slides. Slope movement in general is a major process of the geologic environment that places constraints on engineering development. In order to understand and foresee both the causes and effects of slope movement, studies must be made on a regional scale, at individual sites, and in the laboratory.Areal studies — some embracing entire countries — have shown that certain geologic conditions on slopes facilitate landsliding; these conditions include intensely sheared rocks; poorly consolidated, fine-grained clastic rocks; hard fractured rocks underlain by less resistant rocks; or loose accumulations of fine-grained surface debris.Field investigations as well as mathematical- and physical-model studies are increasing our understanding of the mechanism of slope movement in fractured rock, and assist in arriving at practical solutions to landslide problems related to all kinds of land development for human use. Progressive failure of slopes has been studied in both soil and rock mechanics. New procedures have been developed to evaluate earthquake response of embankments and slopes. The finite element method of analysis is being extensively used in the calculation of slope stability in rock broken by joints, faults, and other discontinuities.RésuméLes éboulements de terrain peuvent créer des perturbations séismiques; ils peuvent également résulter de perturbations séismiques, et des éboulements produits par tremblement de terre ont coûté des vies dans plusieurs pays. Les éboulements peuvent entraîner des inondations désastreuses, particulièrement quand les barrages de matériel éboulé en travers d’un fleuve se rompent, les inondations peuvent déclancher des éboulements. Le mouvement de masse sur les pentes est en général un processus majeur de l’environnement géologique qui place plusieures contraintes sur les développements de la science de l’ingénieur. Pour comprendre et prévoir à la fois les causes et les effets des mouvements de masse sur les pentes, il faut faire des études à l’échelle régionale, au niveau du site particulier et dans le laboratoire.Les études régionales, certaines couvrant des pays entiers, ont montré que certaines conditions géologiques sur les pentes facilitent les éboulements de terrain; ces conditions englobent les roches intensément cisaillées, les roches finement fragmentées et pauvrement consolidées, les roches dures fracturées reposant sur des roches moins résistantes, ou les accumulations meubles de fin matériel de surface.Les études de terrain, aussi bien que les études de models mathématiques et physiques, augmentent notre compréhension des mécanismes à la base des éboulements dans des roches fracturées; elles aident à trouver des solutions pratiques au problème des éboulements de terrain ayant trait à de nombreuses activités humaines. La rupture progressive des pentes a été étudiée à la fois en mécanique des sols et en mécanique des roches. De nouveaux procédés ont été développés pour évaluer la réaction des pentes et des talus aux tremblements de terre. La méthode de l’élément fini est utilisée très fréquemment pour le calcul de la stabilité des pentes dans les roches fracturées par des diaclases, par des failles, et par d’autres discontinuités.

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