Estimating unsaturated hydraulic properties by transient evaporation method in soft rock in Rokkasho area, Japan.

Abstract

As sedimentary soft rock has a potential to store hazardous nuclear waste, several countries utilize it as a possible and safe way of hazardous nuclear waste disposal. Therefore, precise estimation of unsaturated hydraulic properties is needed on the unsaturated flow of this type of rocks to assure the safety of the disposak In this study, Tertiary sedimentary soft rock samples were collected from Rokkasho Low Level Waste Disposal site in Japan. Applicability of an empirical model; Campbell (CB) model, which use commonly for soil hydraulic property estimation was studied. This model was applied to one dimensional flow induced by evaporation in three Pumice Tuff specimens and three Sandstone specimens. The inverse estimation technique was used to select the best parameter in each model by adopting Genetic Algorithm (GA) as an optimization tool. From the results it was clearly found that the unsaturated hydraulic properties could be easily estimated by CB model and the measured evaporation change could be well analyzed. According to the results the CB model is robust for unsaturated flow analysis in soft rock.