Static soil liquefaction entails the sudden loss of strength of loosely packed saturated sand or silt, resulting in a sudden collapse of the sand body. Contrary to “ordinary” slope failure, in which the instable soil mass slides along a clear rupture surface while staying more or less intact, in a liquefaction flow slide the instable mass of sand (or silt) flows laminar like a viscous fluid.
Generally, for static liquefaction in an under-water slope the following conditions are required (1) the presence of a sufficiently large zone of loosely packed, non-lithified, and water-saturated sand or silt; (2) the stress state of the loosely packed sand elements should be close to the so-called metastability point (i.e. the intermediate maximum in the stress path). For this, both mean stress and shear stress should be sufficiently large, which is only the case in a sufficiently high and steep slope; and (3) the presence of a trigger, for example a (small) load change.
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