Indirect Measurement of Suction

Abstract

This paper reports on indirect soil suction measurement methods. Indirect suction measurement techniques measure the moisture equilibrium condition of the soil instead of suction. The moisture equilibrium condition of the soil can be determined by primary means as in vapor pressure, secondary means as through another porous medium or tertiary means as in measuring other physical properties of the porous medium that indicates its moisture equilibrium condition. Indirect suction measurement techniques employing primary means include thermocouple psychrometers, transistor psychrometer and chilled-mirror psychrometer. Indirect suction measurement techniques employing secondary means includes the filter paper method and indirect suction measurement techniques employing tertiary means include thermal conductivity sensors and electrical conductivity sensors. These techniques have been widely used in engineering practice and in research laboratories. However, each of these techniques has its own limitations and capabilities, and active research into improving these techniques is ongoing in universities, research laboratories, and private sector. This paper outlines working principles, calibration, measurement, and application areas of these methods based on recent literature and practice.

A review of the methods available for estimating soil moisture and its implications for water resource management

“…The large sampling volume (up to 8 cm radius) is an advantage in field studies. The biggest limitation of this technique is the dissolution and degradation of the gypsum block (International Atomic Energy Agency, 2008) and need for recalibration with time (Bulut and Leong, 2008). The gypsum block is affected by salt and temperature, resulting in errors (> ±0.01 ft 3 ft À3 ) in moisture estimation (Erlingsson et al, 2009).…”

Soil–water retention curves and microstructures of undisturbed and compacted Guilin lateritic clay

“…Basically, the filter paper reaches equilibrium with the soil either through vapor (total suction) or liquid flow (matric suction). At equilibrium, the suction value of the filter paper and the soil is identical in a constant temperature environment, by giving a sufficient time (Bulut and Leong 2008).…”

Evaluating Performance of a Chilled Mirror Device for Soil Total Suction Measurements

“…The principle involved in measuring the total suction with WP4 is based on equilibrating the liquid phase of the water in soil with vapor phase in the air above the soil sample in a closed chamber (Bulut and Leong 2008). In the chilled mirror equipment, there is a Peltier cooling device to cool the mirror until dew forms and then to heat the mirror to remove the dew.…”

“…Some of them are indirect methods which use another medium to determine the suction and others are direct methods (Bulut and Leong 2008). Each method has its own assets and drawbacks in the reliability, cost and practicality.…”