Soil–water characteristic curves and hydraulic conductivity of Gaomiaozi bentonite pellet-contained materials

Abstract

The bentonite pellet-contained material (PCM) is a feasible material for the joint sealing of high-level radioactive waste repository. During the operation of the repository, the PCM will be unsaturated for a long time, and its water retention and permeability directly affect the buffer barrier seepage, nuclide migration, and joint healing. Moreover, the particle size of bentonite pellets and dry density are important factors affecting the performance of PCM. In this work, the pressure plate method and vapour equilibrium technique were utilized to test the soil-water characteristic curves (SWCCs) of the PCMs with different particle sizes and dry densities. The unsaturated hydraulic conductivity of the PCMs was predicted by combining the SWCC model and saturated hydraulic conductivity. The results showed that in the low suction range (20-1150 kPa), the dry density and particle size had a negative correlation with the water content at the same suction. In the high suction range (4200-309000 kPa), the dry density and particle size had little effect on the SWCC. The Gardner model was appropriate for describing the SWCC of PCM.In addition, the hydraulic conductivity of the PCM decreased with the increase in dry density, while increased with the increase in particle size. The in uence mechanism of the SWCC and hydraulic conductivity was further discussed based on the scanning electron microscopy images and pore size distribution curves.

Evaluation of Soil-Water Characteristic Curves for Different Textural Soils Using Fractal Analysis

“…When fine particle content increases, the pore size formed in the soil decreases, but the porosity may increase [26]. Zhu et al [27] researched the impacts of soil particle size on SWCCs for the Gaomiaozi (GZM) bentonite pellet-contained material, a Na-bentonite found from Inner Mongolia, China, under different suction ranges. Based on their results, the SWCC was less affected by soil particle distribution under high suction, but was more sensitive to particle size under low suction.…”

Modeling the Salinity Effect on the Water Retention Curve of Geosynthetic Clay Liner (GCL) on the Drying Path

“…The water retention curve (WRC) describes the relationship between water content and suction in unsaturated soils. The WRC can be used to estimate the properties of soil under unsaturated conditions including permeability, volume change, deformability, and shear strength [16][17][18][19]. The existing literature shows that the influence of density and salt solution concentration has been considered in the study of WRC, and the concentration of porous fluid has a significant influence on the shape of WRC, but most studies of the water retention performance of GCLs are limited to the wetting path [1,[20][21][22].…”

“…Alterations in pore water chemistry from ground water infiltration can impact the microstructure of the compacted bentonite owing to cation exchange and changes in diffuse double layer thickness [24,25]. The presence of these cations significantly influences the water retention behavior of GCLs, consequently affecting their overall performance and effectiveness as barrier systems [17,21,23]. The hydration electric double layer refers to the interface between the solid particles of the GCL and the surrounding fluid, which is influenced by the presence of charged ions.…”

“…When leachate interacts with the GCL, the exchangeable cations in the leachate migrate to the GCL's surface, leading to changes in the electric double layer. These changes, in turn, impact the function of the GCL to retain water and control its movement [4,7,15,17,21]. Understanding the water retention performance of GCLs under various salt concentrations is crucial to evaluating their longterm serviceability.…”