Comparative Analysis of Water Retention Curves of Residual Soils of Gneiss, Granite and Diabase, Compacted under Optimum Moisture Conditions

Three Brazilian tropical soils are studied: residual soil of diabase, granite, and gneiss. The water retention curves of these soils were determined using compacted specimens under the optimum moisture conditions of their respective compaction curves. For the residual soil of gneiss, water retention curve was obtained with the use of suction plate, pressure plate, and filter paper. Granite and diabase residual soils have the water retention curves determined using filter paper technique following the drying path after initial saturation of the specimen. Characterization tests, determination of the grain size distribution curve, and resistance parameters were made to complement the experimental studies. The higher compaction density of the granite residual soil, associated with its higher clay fraction, is reflected in a higher air entry value. For water moisture contents of less than 25%, a stabilization of volumetric variations of the tested specimens during the drying procedure is observed in order to determine the water retention curve.