Speaker
Description
For the final disposal of radioactive waste in salt formations, researchers are examining not only the stabilizing function of granular salt as a backfill material but also its ability to act as a barrier against incoming and outgoing fluids.
The time required to compact initially loose granular salt into an impermeable backfill is foremost determined by the on-site rate of cavity convergence. However, this rate depends – along with other environmental factors – on the dynamically increasing load resistance of the salt backfill, which, in turn, is controlled by a range of complex interacting factors, whose relative contributions have not yet been fully quantified.
In an empirical approach, we re-evaluate 17 oedometric compaction tests, in which the increase of backfill resistance was experimentally determined for varying boundary conditions.
First, we show to what extent the increase varies across all experiments. Subsequent, we highlight how this variation correlates with the deliberately varied test conditions, foremost compaction rate and initial humidity. To this end, polynomial models of varying degree were fitted to each experiment. Based on the adjusted coefficient of determination ($R^{2}_{adj}$), a fourth-degree polynomial was found to provide the best representation of the observed variability ($R^{2}_{adj} = 0.3$).
When fitting prediction models based on data grouped by compaction rate ($6.9*10^{-6}$ 1/s, $6.9*10^{-7}$ 1/s, $6.9*10^{-8}$ 1/s, $6.9*10^{-9}$ 1/s) the mean adjusted $R^{2}$ improves over all groups to $0.6$. While this illustrates that a generalized, empirical model may benefit from incorporating a compaction rate parameter, it remains uncertain whether the model can be enhanced by further parametrization of other influencing factors, too, like humidity or grain size. Here, we present our current work addressing this challenge, arising from the complex interplay of multiple deformation mechanisms that give rise to interdependent relationships among the governing factors.