A New Triaxial Testing System for Unsaturated Soil Characterization

Abstract

Suction-controlled triaxial tests have been widely used to characterize unsaturated soils. However, this type of test requires sophisticated and therefore expensive equipment, and is very time consuming because of the low permeability of unsaturated soils. Only a few research universities can afford the equipment, which limits the advancement and implementation of unsaturated soil mechanics. This paper proposes a new triaxial testing system for unsaturated soils based upon minor modifications on the conventional triaxial test apparatus for saturated soils. Instead of controlling suction, high-suction tensiometers are adopted to monitor matric suction variations during constant water content triaxial testing. Also, a photogrammetry-based method is used to measure volume changes of unsaturated soil specimens during triaxial testing. To evaluate the capabilities of the proposed testing system, a series of constant water content triaxial tests were performed on unsaturated soils with different moisture content. Matric suction and volume variations during testing were monitored by the high-suction tensiometers and the photogrammetry-based method, respectively. New methods were also proposed to analyze the test results. Analysis results showed that the proposed system is cost effective and efficient for unsaturated soil characterization.