Landslides: Investigation and Mitigation. Chapter 24 - Soft Sensitive Clays

Soft sensitive clays, also termed quick clays, exhibit a sensitivity greater than 30 and have a remolded shear strength less than 0.5 kPa. Remolding following a landslide in soft sensitive clays results in drastic reduction in shear resistance, causing the remolded clay to behave like a thick liquid so that the slide mass moves away and leaves the new slope unsupported. A new instability may result and a series of retrogressive failures will be triggered that can extend far beyond the crest of the initial slope. In highly sensitive clays, therefore, it is not just the risk of a slope failure that is of concern, but also the area that can be affected by retrogressive sliding. At present, the risk and extent of retrogression are difficult to evaluate. This chapter on soft sensitive clays focuses on the following: their description; valley formation and groundwater regime; stability analysis; and establishing the risk of retrogression.