On Preferred Saturation Methods for Geotechnical Flow Tests

Abstract Laboratory flow tests performed on granular materials in rigid-wall permeameters are used to determine the hydraulic conductivity of saturated materials or to study particle migration. For such tests, specimen preparation is important, particularly the saturation process. The presence of gas bubbles in the tested specimen leads to smaller hydraulic conductivity values and may affect particle migration. Therefore, measures must be taken to obtain fully saturated specimens. In order to improve saturation, two elements have to be taken into consideration: first, the presence of gas in the permeant water; second, the presence of gas in the pores of the specimen. Several flow tests are described in ASTM standards. These standards involve different conditioning methods for permeant water (e.g., heating, seepage through a sand filter, cavitation under vacuum), and different specimen saturation methods (e.g., saturation with an upward flow under vacuum, following carbon dioxide flushing). In this article, water deaeration and specimen saturation methods were evaluated and compared using a mass-volume method. In the first phase, the importance of using deaerated permeant water was examined by comparing different conditioning methods for permeant water. Saturation using water in equilibrium with atmospheric pressure was compared with saturation with water heated at 40°C, water deaerated using a sand filter, and water deaerated by cavitation under vacuum. In the second phase, the influence of purging the gas contained in the soil specimen before saturation using carbon dioxide or a vacuum was compared. In both cases, the permeant water was deaerated by cavitation under vacuum. These tests showed that combining a purge of the specimen with carbon dioxide with saturation using an upward flow of water deaerated by cavitation under vacuum yielded the highest degree of saturation for granular specimens in a rigid-wall permeameter. Another advantage of this combination is that it accelerates specimen saturation.