A new simple system for measuring volume changes in unsaturated soils

• Published in: Canadian geotechnical journal Vol. 39; no. 3; pp. 757 - 764
• Main Authors: Ng, C W.W, Zhan, L T, Cui, Y J
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.06.2002; National Research Council of Canada; Canadian Science Publishing NRC Research Press
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Engineering geology; Exact sciences and technology; Soils; Testing; experimental studies; triaxial tests; deformation; creep; accuracy; pressure; loading; soils; correlation coefficient; calibration; unsaturated zone
• ISSN: 0008-3674; 1208-6010
• DOI: 10.1139/t02-015

A new simple system for accurately measuring overall total volume changes in unsaturated soil specimens with a triaxial apparatus is introduced in this paper. The basic principle of the measuring system is to record changes in the differential pressure due to changes in the water level inside an open-ended, bottle-shaped inner cell caused by volume change in the specimen and inside a reference tube using an accurate differential pressure transducer. Several important steps were taken to improve the accuracy and sensitivity of the measuring system. Detailed calibrations were carried out to account for apparent volume changes as a result of changes in cell pressure, fluctuation in the ambient temperatures, creep in the inner cell wall, and relative movement between the loading ram and the inner cell. The calibration results demonstrate that the measuring system is reasonably linear, reversible, and repeatable. The estimated accuracy of the measuring system is in the order of 32 mm 3 (or 0.04% volumetric strain for a triaxial specimen 38 mm in diameter and 76 mm in height) once the system is properly calibrated.Key words: unsaturated soils, volume-change measurement, open-ended, bottle-shaped, inner cell, differential pressure, calibration.