Abstract: Filter paper method is an indirect method to measure unsaturated soil suction, and it is necessary to get the calibration curve which can express the relationship between soil suction and filter paper’s moisture content before the suction of the soil is determined by filter paper method. This paper introduces researchers related researches in the calibration curve of Whatman No.42, Schleicher & Schuell No.589 and domestic Shuang-quan quantitative filter paper; it is found that the researches considering the temperature effect of filter paper’s calibration curve is still rare. The domestic Shuangquan 203 filter paper’s wetting calibration curve respectively at 20 ℃, 25 ℃, 30 ℃ and 40 ℃ is obtained by utilizing NaCl solution at different molar concentrations. The experimental results show that the water retention capability of filter paper is decreased with the increasing of temperature; and temperature has a greater impact on the water retention capability of filter paper when filter paper is in the period of low suction. The filter rate equation considering the effect of temperature is established by multiple linear regression analysis. The microscopic structure of filter paper is observed; and by means of surface chemistry theory, the mechanism of temperature effect on the filter paper rate curve is analyzed.

Key words: temperature effect, filter paper method, calibration curves, unsaturated soil