Study of suction-water content calibrations for the Whatman No. 42 filter paper

Abstract

The filter paper method (FPM) is probably the simplest of the methods available for estimating the soil suction (s). The FPM can be used over a wide suction range (30 kPa < s < 30000 kPa). The FPM calculates soil suction indirectly by measuring the gravimetric water content (w) of the filter paper at equilibrium that is related to soil suction through a predetermined s-w calibration curve. A number of s-w calibration functions for the Whatman No. 42 filter paper have been published in the literature. This paper presents and discusses graphical and statistical comparisons of several calibrations (bilinear and single equations) proposed at the literature for the Whatman No. 42 filter paper for different levels of suction. The results show that the variations observed in the evaluated calibrations are smaller than the expected variability observed in the established techniques for measuring or controlling soil suction for 30 kPa < s < 10000 kPa.