Site water salinity effect on the hydro-mechanical behavior of compacted GMZ bentonite with technological void

Abstract

The hydromechanical behavior of compacted bentonite in near-field salinity groundwater environment is of great importance for achieving the low-permeability sealing capacity in deep geological repositories. Within this context, swelling pressure and hydraulic conductivity of compacted bentonites with technological voids were evaluated under simulated site water salinity conditions. Water content, dry density and pore size distribution were measured after hydration. Results showed that the swelling pressure shows a trend of rapid rise and reach the peak value, then drop sharply and stabilized. The rapid decrease in the hydraulic conductivity for all salinity is the salient features, and then, it reduces slowly. The above evolution behavior is dominated by the swelling mechanisms and the self-sealing of technological void under different salinity conditions. Adequate water and space provided by technological void lead to gradient evolution of geotechnical properties, such as water content, dry density and pore size distribution. The density increase mechanism derived from salinity fails to compete with the density decrease mechanism derived from sufficient space sourced from technological void. Therefore, the dry density at the external sampling site decreases with increasing salinity. At high salinity, the compressed diffuse double layer not only increases the inter-aggregate pores but also widens the water flow channels. As a result, hydraulic conductivity increases with increasing salinity. Considering the influence from groundwater salinity, it is necessary to improve basic properties and technological void dimensions of bentonite blocks for the safety of long-term operation of deep geological repository.