Inflow scenarios for a deep geological repository imply that two distinct phases, a gaseous and a liquid phase, can be found in the pore space. The wetting dynamics depend strongly on two constitutive relations (CR): the capillary pressure-saturation relation (CPS) and the relative permeability-saturation relation. Knowledge of these CRs is thus a prerequisite for modelling flow into borehole or drift backfill during the post-operational phase.

In a repository in rock salt the lithostatic load leads to drift and borehole convergence. Backfill consisting of crushed salt is subject to compaction and concurrent decrease of the pore space which has in turn a strong impact on the CRs for two-phase flow. Presented here are first results of still ongoing tests on CRs for potential backfill material, envisaged for a German repository, at different compaction levels.

The CPS-curves derived so far show similar characteristics as the curves for common soils along with the expected increase at decreasing porosity. The relative gas permeability, however, cannot be fitted to classic approaches like the well-known equations of Brooks and Corey. The hydraulic behaviour of the material is thus not yet understood deeply enough to allow reliable model predictions and requires further investigations.