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

Waseda University, Global Center for Science and Engineering, 3-4-1 Ohkubo, Shinjuku-ku, Japan

^* Corresponding author: whlxy2002@aoni.waseda.jp

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 (p_s) 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 p_s. For instance, test duration is typically 1-2 month for a specimen with thickness (h_sp) of 20 mm, and 1-2 weeks for h_sp= 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 h_sp= 2 mm specimens to measure p_s, 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 p_s for h_sp= 0.4 mm specimen, by which testing duration can be reduced to 1-2 hours. The p_s 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 h_sp=0.4 mm specimens.