Experimental Study on the Intrusion/Erosion Behavior of GMZ Bentonite Considering Fracture Aperture Effects

Abstract

AbstractIntrusion/erosion will cause mass loss of bentonite, resulting in endangering the operation safety of the repository for disposal of high-level radioactive waste. In this work, intrusion/erosion tests were conducted on GMZ bentonite specimens with a fracture aperture of 0.1, 0.5, 0.75 and 1.0 mm, as well as a duration of 60 days. Images were regularly captured with a digital camera. The intrusion distance and width of accessory-mineral ring were obtained. The erosion rate was determined by a turbidimeter. Meanwhile, parallel tests with a fracture aperture of 0.5 and 1.0 mm were repeated with a duration of 5, 15 and 30 days. After tests stopped, dry weight of specimens was measured. Results show that the intrusion distance increased with increasing fracture apertures, resulting in the increase of accessory-mineral-ring width, which will in turn restrict intrusion and erosion. Actually, the erosion rate in the early period decreased obviously with increasing accessory-mineral-ring widths, due to its filtration effects. However, when erosion reached stabilization, the erosion rate increased with increasing fracture apertures and intrusion distances but not independent of the accessory-mineral ring. The majority part of specimen mass loss ratio in the early period was from intrusion. But when intrusion reached stabilization, the mass loss ratio of specimen will be mainly contributed by erosion and would keep on increasing. Moreover, the mass loss ratios of specimens after 60 days by intrusion and erosion both increased with increasing fracture apertures. Meanwhile, the difference between the mass loss ratio by intrusion and erosion increased with increasing fracture apertures.