Evaluation of Soil Suction from Filter Paper

Soil suction is a useful parameter for characterizing the effect of moisture on the volume change behavior of cohesive soil. Soil suction can be described as a measure of the pulling or tension force per unit area exerted on pore water. Two often-used energy methods for determining soil suction are the thermocouple psychrometer method and the filter paper method. In this study, laboratory suction tests were performed on 24 undisturbed soil samples to evaluate the filter paper method with respect to the thermocouple psychrometer method. The filter paper method is simple and requires little special equipment; however, the validity of filter paper as a useful tool for characterizing swelling behavior has not been well-established. The results of the study show that the filter paper method, as it was employed in this study, is as reproducible as the thermocouple psychrometer method. For the soils tested, comparisons of parameters generally found useful for characterizing swelling behavior showed that the filter paper method usually indicates less capability for swell than the thermocouple psychrometer method. This conclusion is especially significant since predictions of heave based on suction data from thermocouple psychrometers indicate higher levels of heave than those actually determined in the field. (Author)