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Title: An evaluation of the thermocouple psychrometric technique for the measurement of suction in clay soils
Authors: Johnson, Lawrence D.
Keywords: Negative pore water pressure
Clay soils
Soil properties
Soil mechanics
Soil suction
Thermocouple psychrometers
Publisher: Soils and Pavements Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: Suction or negative pore water pressure is important in controlling the physical properties of less than fully saturated soils. Methods for the accurate measurement of a wide range of suctions in such soils are not well known and are under development. This study to evaluate the thermocouple psychrometers as a technique for the measurement of suction was initiated because these devices are relatively inexpensive, simple to use, allow rapid measurements, and possess a large range. An apparatus was designed, constructed, and tested for the thermocouple psychrometric measurement of suction pressure in clay soils without the need for preci se t emperature control. This report reviews the background literature leading to the development of the apparatus, describes the equipment, outlines procedures for making psychrometric measurements. A study of various types of thermocouple psychrometer s showed that psychrometers with 1- or 2-mil-diam chromel-constantan thermocouples provide a range of total suction up to about 90 atm. The reproducibility is about ± 1 atm or less for suctions less than 50 atm and about ± 2 atm for suctions greater than 50 atm. Suction measurements of Yazoo clay from Jackson, Mississippi, and clay from the weathered Upper Midway formation, Lackland Air Force Base, Texas, support the definition that total suction is the sum of matrix and osmotic components.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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