Update on dilatancy associated with onset of gas flow in Callovo-Oxfordian claystone. Progress report on test SPP_COx-2

This report describes in detail the stress-path permeameter (SPP) apparatus and the on-going second test conducted on Callovo-Oxfordian (COx) claystone from the Bure underground research laboratory (URL) in France. Funding for this study has been provided by the French radioactive waste management operator, Andra, the European Union (FORGE Project, Project number 230357) and the British Geological Survey through its well-founded laboratory programme and the Geosphere Containment project (part of the BGS core strategic programme). The results from test SPP_COx-2 clearly show that at the onset of gas propagation through the test sample dilatancy is observed in three radial and one axial direction. A component of this dilatancy is associated with changes in pore pressure. However, pore-pressure variation cannot account for the full amount of strain recorded and a proportion of the strain observed is the result of gas migration by dilatant pathway formation. The test is on-going and more insight will be achieved once the test is complete.