Characterisation of the hydraulic properties within the EDZ around drifts at level −490 m of the Meuse/Haute-Marne URL: A methodology for consistent interpretation of hydraulic tests

In order to investigate potential changes of the hydraulic properties of the EDZ over time in the Meuse/Haute-Marne underground research laboratory (URL), several hydraulic tests campaigns have been carried out between 2005 and 2008 in dedicated boreholes. After several test series, inconsistencies were noticed in the results, indicating, in particular cases, erratic, inexplicable property changes over time and spatial contrasts. It was therefore difficult to determine reliably potential trends of the EDZ hydraulic properties. It appeared necessary to re-evaluate both the interpretation concepts and assumptions applied to the numerical analyses of test data on the EDZ, trying to better constrain the flow model and the parameter variables. In order to improve the understanding of the geometrical, geomechanical and hydraulic properties of the EDZ, independent information from other investigation methods has been used to critically revise the conceptual model and formation parameters. In particular, results from a diffusion experiment and ultrasonic measurements allowed constraining the extent of the mechanical damaged zone around the borehole (BDZ). Storativity parameters were fitted due to their expected variability. Indeed, high storativity values can be presumed under the unsaturated conditions of the EDZ. The results of the reanalyses, performed with the numerical borehole simulator MULTISIM, demonstrated the good quality and consistency of the revised conceptual model with constrained BDZ and variable storativity. Overall the new simulation results obtained from selected test series are now very consistent. The revised conceptual model demonstrated its capacity to better represent the evolution and extension of the EDZ around a drift in Meuse/Haute-Marne URL. Further consistency checks are proposed to confirm the new model assumptions and the estimates of the single phase flow model in the EDZ.

► We investigate potential changes of the hydraulic properties of the EDZ.
► After several hydraulic test series, inconsistencies were noticed in the results.
► In particular cases, inexplicable property changes over time and space were noticed.
► Information from other investigation methods helped to critically revise the conceptual model.
► The revised conceptual model represents better the evolution and extension of the EDZ.