Residual strength of clays in landslides, folded strata and the laboratory

作者：Alec Westley Skempton · 发表于：Géotechnique · 年份：1985 · DOI：10.1680/geot.1985.35.1.3 · 被引用次数：903 · 研究领域：Landslides and related hazards、Soil and Unsaturated Flow、Geotechnical Engineering and Soil Mechanics

The post-peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages. First, at relatively small displacements, the strength decreases to the ‘fully softened’ or ‘critical state’ value, owing to an increase in water content (dilatancy). Second, after much larger displacements, the strength falls to the residual value, owing to reorientation of platy clay minerals parallel to the direction of shearing. If the clay fraction is less than about 25% the second stage scarcely comes into operation; the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20°. Conversely, when the clay fraction is about 50%, residual strength is controlled almost entirely by sliding friction of the clay minerals, and further increase in clay fraction has little effect. The angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15° for kaolinite, 10° for illite or clay mica and 5° for montmorillonite. When the clay fraction lies between 25% and 50% there is a ‘transitional’ type of behaviour, residual strength being dependent on the percentage of clay particles as well as on their nature. The post-peak drop in strength of a normally-consolidated clay is due only to particle reorientation. Measurements of strength on natural shear surfaces agree, within practical limits of variation, with values derived from back analysis of reactivated landslides....