A device to measure apparent swelling pressure of compacted bentonite using extremely thin specimen

Abstract

As a candidate material proposed for the geological disposal of the high level radioactive waste, bentonite has been studied extensively in terms of its engineering properties. One of the properties is the pressure generated during wetting compacted bentonite under rigorously confined condition. This pressure is designated apparent swelling pressure (ps) herein. On the other hand, due to the extremely low hydraulic conductivity (e.g. 10-9-10-14 m/s) of compacted bentonite, it is often very time consuming to measure ps. For instance, test duration is typically 1-2 month for a specimen with thickness (hsp) of 20 mm, and 1-2 weeks for hsp= 10 mm. Though testing duration can be reduced by using thinner specimens, it becomes difficult to control measurement accuracy. Recently, the author reported a series of datasets obtained with newly developed testing method using hsp= 2 mm specimens to measure ps, by which testing duration was reduced to 1-2 days and data repeatability was also extraordinarily good. In this paper, the author made further developments on such testing techniques and introduced a device to measure ps for hsp= 0.4 mm specimen, by which testing duration can be reduced to 1-2 hours. The ps measured by this device on a bentonite was compared with previous database, which implies that data repeatability is very good in generally, though the data scattering is observed for hsp=0.4 mm specimens.