Anhydritic Aquisalids (UAEKST, Fig. 5.18, p. 65)
Aquisalids are the salty soils in wet areas in the deserts where capillary rise and evaporation of water concentrate the salts near the surface. Some of these soils have redoximorphic depletions and concentrations. In other soils redoximorphic features may not be evident because of a high pH and the associated low redox potential, which inhibit iron and manganese reduction. These soils occur dominantly in depressional areas where ground water saturates the soils at least part of the year. The vegetation on these soils generally is sparse, consisting of salt-tolerant shrubs, grasses, and forbs. Although these soils may hold water at a tension less than 1500 kPa, the dissolved salt content makes the soils physiologically dry.
Anhydritic Aquisalids have an anhydric horizon within 100 cm of the soil surface. The anhydritic horizon is a horizon in which anhydrite has accumulated through neoformation or transformation to a significant exent. It typically occurs as a subsurface horizon. It commonly occurs in conjunction with a salic horizon.
Anhydrite is a mineral—anhydrous calcium sulfate, CaSO4. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The hardness is 3.5 and the specific gravity 2.9. The color is white, sometimes greyish, bluish, or purple. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to ~200°C under normal atmospheric conditions. Anhydrite is commonly associated with calcite and halite.
Identification of anhydrite is important when determining soil strength. Soils high in anhydrite exhibit fluidity and lack soil strength and load bearing capacity. Moisture content strongly influences soil’s consistence and a water table is commonly within the soil profile. The manner in which specimens of soil fail under increasing force ranges widely and usually is highly dependent on water state. To test for fluidity, a handful of soil material is squeezed in the hand. For moderately fluid materials after exerting full pressure, most flows through the fingers; a small residue remains in the palm of the hand.
For example, if some of the soil flows between the fingers with difficulty, the n value is between 0.7 and less than 1.0 (slightly fluid manner of failure class); if the soil flows easily between the fingers, the n value is 1 or more (moderately fluid or very fluid manner of failure class) depending on what remains in the palm of the hand.
Refer to:
Anhydritic Aquisalids (UAEKST, Fig. 5.18, p. 65)
Aquisalids are the salty soils in wet areas in the deserts where capillary rise and evaporation of water concentrate the salts near the surface. Some of these soils have redoximorphic depletions and concentrations. In other soils redoximorphic features may not be evident because of a high pH and the associated low redox potential, which inhibit iron and manganese reduction. These soils occur dominantly in depressional areas where ground water saturates the soils at least part of the year. The vegetation on these soils generally is sparse, consisting of salt-tolerant shrubs, grasses, and forbs. Although these soils may hold water at a tension less than 1500 kPa, the dissolved salt content makes the soils physiologically dry.
Anhydritic Aquisalids have an anhydric horizon within 100 cm of the soil surface. The anhydritic horizon is a horizon in which anhydrite has accumulated through neoformation or transformation to a significant exent. It typically occurs as a subsurface horizon. It commonly occurs in conjunction with a salic horizon.
Anhydrite is a mineral—anhydrous calcium sulfate, CaSO4. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The hardness is 3.5 and the specific gravity 2.9. The color is white, sometimes greyish, bluish, or purple. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to ~200°C under normal atmospheric conditions. Anhydrite is commonly associated with calcite and halite.
Identification of anhydrite is important when determining soil strength. Soils high in anhydrite exhibit fluidity and lack soil strength and load bearing capacity. Moisture content strongly influences soil’s consistence and a water table is commonly within the soil profile. The manner in which specimens of soil fail under increasing force ranges widely and usually is highly dependent on water state. To test for fluidity, a handful of soil material is squeezed in the hand. For moderately fluid materials after exerting full pressure, most flows through the fingers; a small residue remains in the palm of the hand.
For example, if some of the soil flows between the fingers with difficulty, the n value is between 0.7 and less than 1.0 (slightly fluid manner of failure class); if the soil flows easily between the fingers, the n value is 1 or more (moderately fluid or very fluid manner of failure class) depending on what remains in the palm of the hand.
Refer to: