An Investigation in the Influence of Contact Angle on Soil Water Characteristic Curve with a Modified Capillary Rise Method

摘要

Contact angle quantifies the physicochemical interactions at the liquid-solid interface andis therefore critical to many physical processes involving the interaction of soil and water.In geotechnical engineering, such interactions are the basis for the formulation of the SoilWater Characteristic Curve (SWCC). However, the role of contact angle in SWCCs hasnot been adequately recognized. This paper reports a comprehensive study on applyingCapillary Rise Method (CRM) to measure the contact angles of soils. Analytical solutionsto two forms of the Lucas-Washburn equation were presented to provide the theoreticalbasis for applying CRM to soils. The disadvantages of conventional CRM analyses weredemonstrated with experiments. A modified CRM was proposed based on an analyticalsolution to a more complicated form of the Lucas-Washburn equation. This modifiedCRM exhibited reliable performance on numerous specimens made of a subgrade soiland a silicon dioxide sand. Testing procedures were designed and strictly followed, andinnovative apparatuses for the preparation, transport, and accommodation of soilspecimens were fabricated to ensure repeatability. For the modified CRM, experimentresults for virgin specimens demonstrated good repeatability; while for sieved soils, cleartrends were observed in the variations of contact angle with respect to pore size. Contactangles much greater than zero were observed for all of the tested specimens whichcontradicts the assumption of perfect wettability in previous SWCC studies. In addition,it was demonstrated that neglecting the variations of contact angles with respect to poreradius could result in significant errors in the SWCC construction.