Calibration curves of two filter papers at high suction and temperature and their application

Buffer/backfill materials may experience temperature change in several circumstances, and thus it is necessary to study the hydro mechanical behaviour of soils at different temperatures. The filter paper method is an indirect way to conduct the suction measurement. The filter method can cover the full range of suction measurement, and it is inexpensive and relatively simple. The calibration curves for Whatman No. 42 and Double-circle No. 203 filter papers are investigated at room temperature by many researchers. However, the suction and temperature are both relatively low. This study presents the results of an experimental investigation of thermal effects on the calibration curves of the filter papers Whatman No. 42 and Double-circle No. 203 and the application of the curves to obtain the total suction of a compacted bentonite at different temperatures. The calibration curves between the suction and moisture content for the filter papers are determined at 20,40,60 and 80, respectively, by the vapor equilibrium technique using fifteen types of saturated salt solutions. The results show that the water-retention capacity of the filter paper decreases with the increasing temperature. The obtained calibration curves are used to determine the water-retention behaviour of GMZ Ca-bentonite, which is considered as a possible backfill material in the high level radioactive waste deep geological disposal project in China, at 20, 40, 60 and 80, respectively. It is found that the water-retention curves of the bentonite are both the same using the two kinds of filter papers, and they decrease clearly with temperature, especially when it is above 60. In addition, the water-retention capacity in the range of higher suction is slightly affected by temperatures.