Experimental study of water retention characteristics and vapor migration of earth material under relative humidity variation

The variation of relative humidity induces the migration of vapor, which has an important effect on the strength and deformation of earth. The sorption-desorption and migration of vapor inside the earth are of great significance for revealing the disease breeding mechanism of earth structure. Aiming at two different earth materials named STR and CRA chosen from a few existing construction sites located in Lyon region in the southeast of France, the sorption-desorption tests were conducted through two different methods, saturated salt solution method and dynamic vapor sorption (DVS) separately, and the experimental results were compared accordingly. In addition, an innovative apparatus with high-precision strain measuring system was invented and used for monitoring the vapor migration, the variation of relative humidity and gas pressure with time at the top and the bottom of earth specimens was explored, and the deformation characteristics of earth specimens during vapor migration were also analyzed. The experimental results indicate that the sorption curve obtained through DVS is in accordance with that from saturated salt solution method. The sorption curve can be divided into three parts: monolayer adsorption, multilayer adsorption and capillary condensation. Meanwhile, the retention characteristics of earth increases with the rise of clay activity. The retention characteristics have important effect on the relative humidity at the outlet and relative gas pressure at the bottom of specimens. The dilatancy phenomenon occurs during the vapor migration process.