Duricrust, engineering geology
Definition
Duricrust (q.v. in Vols. VI, XII) is a peculiarly Australian term used to describe the case-hardened superficial mantle of rocklike Material that outcrops over much of the arid and semi-arid parts of Australia (Finkl, 1979). Outliers of duricrust also occur in the better-watered parts of the continent. In some places the duricrust has been affected by tectonic movements and has been found covered by more recent sediments in boreholes (Wopfner and Twidale 1967; Finkl and Churchward, 1973).
The material of the duricrust has been formed by physicochemical processes involving reactions between the atmosphere, ground water, and soil and rock. It consists of soil or rock cemented or replaced either by oxides of silicon, iron, or aluminum or by such salts as calcium carbonate or sulfate. The solubilities in water of some of the substances involved in these reactions are shown in Figure 1. Calcium sulfate as gypsum has a constant solubility of 0.2 percent at all pH levels. Where...
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