Relationship between continuous air content and air conductivity in a sandy soil based on acoustic measurements

Abstract

Soil air conductivity has a hysteretic relation-ship with the air content of the soil, likely caused by amount of entrapped air depending on the wetting or dry-ing history of the soil. Entrapped air content can be eval-uated as the difference between total air content according to the volumetric water content and continuous air content based on the acoustic measurements. Acoustic tests were conducted for a 50-cm3 cylindrical container filled with Tottori Dune sand at several stages in the drainage or imbi-bition process. We evaluated a relationship between con-tinuous air content and air conductivity, as well as the ef-fects of entrapped air on the hysteresis. Air was entrapped in the course of imbibition of water for the total air content from 15 % to 10 %. Within this total air content range, air conductivity was found to be uniquely determined with the continuous air content. Since almost no air was entrapped for the total air content exceeding 15 %, continuity of air in the soil depending on wetting or drying was assumed to be a main reason for the air conductivity – total air content hysteresis.