Gas breakthrough tests on saturated GMZ01 bentonite using RCP technique with consideration of dry density effect

抄録

In this study, gas breakthrough tests were conducted on GMZ01 bentonite specimens with dry densities 1.3, 1.5 and 1.7 Mg/m3 under rigid boundary conditions using the residual capillary pressure (RCP) technique. Prior to the gas breakthrough tests, water permeability tests were performed for determining intrinsic water permeability and establishing full water saturation for the follow-up gas breakthrough tests. The intrinsic water permeability measured ranges between 11 and 150 nDarcy (1.10×10-20 and 1.50×10-19 m2). As dry density increases, the residual capillary pressure differences of the initially water-saturated bentonite specimens recorded increase from 0.12 to 0.61 MPa. Meanwhile, the time to breakthrough was recorded to increase sharply as dry density increases. In addition, the maximum effective gas permeability decreases from 8.91×10-18 to 8.92×10-19 m2 as dry density increases from 1.3 to 1.7 Mg/m3. These results indicate that the capillary drainage in the bentonite specimen is highly related to the capillarity effects in the largest pores. The higher dry density, the smaller flow channels, resulting in more difficult for gas phase to dispel water from the interconnected flow pathways and a better sealing capacity with a higher residual capillary pressure.