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In southwest Louisiana, some surface silts (up to 3 feet deep) collapse under load after moisture is added. These soils were indistinguishable from nearby normal silts through routine tests. The deposits occur as low, gently-sloping ridges. Very similar collapsible soils were found in the well-known pimple mounds of the area. In the stable silts, vermiculite is the dominant clay mineral; in the collapsible silts, montmorillonite, Kaoline and illite are also present. Moisture is held in the pores of collapsible silts by electro-chemical forces. When collapsible silts were remolded with water or ethylene glycol (both polar liquids), no water passed through under 2 meters of head. In settled mixtures of collapsible silts and a solution of Calgon, (commercial brand of Sodium Hexameta phosphate) the supernatant liquid was black. The color change is attributed to lignins. Four criteria were established for identifying collapsible silts: an in-place unit weight less than 80 lbs/cu ft; a maximum dry unit weight less than 104 lbs/cu ft; a black liquid after the soil solids have settled out in a 3% solution of Calgon; and a total strain of at least 15% in the collapse test (a modified consolidation test of an oven-dried, undisturbed sample that is then saturated under pressure to 16 tons/sq ft).
Loess is a soil that can exhibit large deformations upon wetting. Cases of wetting induced collapse in loess havebeen documented for natural deposits ...
Collapsible soils are susceptible to large volumetric strains when they become saturated. Numerous soil typesfall in the general category of collapsib...
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