Hydraulic conductivity and swelling ability of a polymer modified bentonite subjected to wet–dry cycles in seawater

Abstract

The performance of clay liners may be impaired when in contact with aggressive solutions due to cation exchange. The efficiency of these liners can further deteriorate if cation exchange is combined with wet and dry cycles as a result of seasonal changes in temperature, rainfall and groundwater migration. The performance of untreated sodium bentonite is compared to the performance of a treated clay, HYPER clay, under wet and dry cycles, in seawater. HYPER clay is a polymer modified bentonite with enhanced performance in presence of electrolyte solutions. In this study, the bentonite is treated with 2% and 8% polymer by dry weight of clay. The swelling ability, self-healing capacity and permeability are investigated by means of swell index tests, one-dimensional swell tests in oedometer cells and hydraulic conductivity tests. The specimens were subjected to 6 wet–dry cycles in swell tests and to 4 cycles in hydraulic conductivity tests.The swell index tests showed that the swelling ability increased as the polymer content increased. Similar results were obtained from one-dimensional swell tests. The height of HYPER clay (8% polymer content) during the sixth wet–dry cycle was still considerably larger compared to the height of the untreated clay. The hydraulic conductivity of untreated sodium bentonite sharply increased within three cycles, while HYPER clay maintained its low permeability to seawater. During the fourth wet–dry cycle, the hydraulic conductivity of untreated bentonite was three orders of magnitude higher than HYPER clay 2%. Sodium bentonite was not able to heal cracks formed during drying, which constitute preferential flow paths for the solution.