Does gravity affect the thermo-hydro-mechanical processes in a bentonite barrier?

Abstract

To simulate in the laboratory the conditions of the buffer material in an underground repository for radioactive waste, three tests were performed in instrumented stainless steel cylindrical cells using compacted Wyoming-type bentonite. One of the cells was laid in vertical position and the other two stayed horizontal during operation, with the aim of checking if the layout of the cell affected the results obtained. At one end of the cells, a heater set at 90°C simulated the waste container. After two months of heating, hydration of the bentonite with a saline groundwater started through the surface of the cell opposite to the heater. One of the horizontal cells was dismantled right after the heating phase. After one year of hydration the other two cells were dismantled and the final physical state of the bentonite was analysed in terms of water content and dry density. It was checked that the spatial layout and hence, the effect of gravity, would only be to some extent noticeable if water vapour is involved, i.e. in those phases or processes in which water vapour movement is relevant (namely heating). In the liquid phase the effect of gravity on the water intake and water content and dry density distribution was not noticeable any more.