ISSN: 1945-7545
Published Online: 6 January 2006
Page Count: 12

Constant Flow Method for Concurrently Measuring Soil-Water Characteristic Curve and Hydraulic Conductivity Function

Lu, N
Professor, Colorado School of Mines, Division of Engineering, Golden,CO

Wayllace, A
Graduate Research Assistant, Colorado School of Mines, Division of Engineering, Golden,CO

Carrera, J
Graduate Research Assistant, Colorado School of Mines, Division of Engineering, Golden,CO

Likos, WJ
Assistant Professor, University of Missouri-Columbia, Columbia,MO

(Received 1 April 2004; accepted 9 December 2005)

Abstract

A constant-flow laboratory testing method (CFM) is presented for concurrently measuring the soil-water characteristic curve (SWCC) and hydraulic conductivity function (HCF) of unsaturated coarse-grained soils. Two computer-automated syringe pumps are employed to control the volumetric water content of a specimen and to periodically impose constant volumetric flow rates through the specimen, respectively. Hydraulic conductivity (k) corresponding to each water content increment is determined from Darcy's law by measuring the steady-state gradient induced by the applied constant flow. Matric suction is maintained by axis translation using elevated pore air pressure and high-air-entry ceramic disks. Diffused air bubbles are removed using unique passive bubble traps. SWCCs and HCFs are obtained for three sandy soil specimens, requiring about 25–35 days to obtain both functions for each soil. The range of the system is demonstrated for k from about 10⁻⁴ cm/s to 10⁻⁹ cm/s at corresponding matric suction between about 0 kPa (saturated) and 40 kPa. Results are validated by comparison with independent SWCC measurements obtained using Tempe cells and HCFs estimated using a statistical model.

Keywords:
unsaturated soil, soil-water characteristic curve, hydraulic conductivity function, matric suction, sandy soil, constant flow method, permeameter

Paper ID: GTJ12637
DOI: 10.1520/GTJ12637
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