Effect of mineralogical composition and pore structure on the swelling of COx claystone
In this study, we use experimental methods to investigate the connections between the mineralogical composition and pore structure of re-sealed Callovo-Oxfordian (COx) claystone. The apparent swelling pressure (Papp) is measured in the absence of confining pressure, to mimic the industrial case (close to excavated and damaged tunnel walls). Quantitative XRD (QXRD) demonstrates that the amount of smectite, which is a swelling clay, present in COx claystone, is weakly correlated with Papp. Meanwhile, the R1-type interstratified illite/smectite (R1-I/S) is highly correlated to Papp. Nitrogen isotherms data imply that the Gurvich total pore volume (VGurvich) and the specific surface area (SSA) are linearly related to R1-I/S. Based on these results, we conclude that nitrogen adsorption tests provide an easier and more effective technique than QXRD for assessing COx swelling capacity, as both VGurvich and SSA have been proven as effective indicators.