Modified Unconfined Compression Testing System to Characterize Stress-Strain Behavior of Unsaturated Soils at Low Confining Stresses


In geotechnical and pavement engineering, many projects involve shallow, unsaturated soil with low confining stress. Suction-controlled triaxial tests usually are used to investigate stress-strain behavior (i.e., deformation and strength) in such soils. However, because they require significant modifications to the conventional apparatus used to test saturated soils and are time-consuming to perform, the tests cannot be justified for time-sensitive engineering projects. A modified unconfined compression testing system is presented to investigate the stress-strain behavior of unsaturated soils at low confining stresses. Negative air pressure (i.e., vacuum) provides the low confining pressure required for the tests, and high-suction tensiometers are used to monitor variations in the soil matric suction during testing. A photogrammetric method is used to reconstruct the three-dimensional model of unsaturated soil specimens, from which total and localized volume changes are calculated. Methods are proposed for unsaturated shear strength analysis. A series of tests was carried out to demonstrate the use of the modified unconfined compression testing system to evaluate the stress-strain behavior of unsaturated soil under different confining stresses. Results indicated that the newly developed modified unconfined compression testing system was a cost-effective method for the rapid evaluation of stress-strain behavior of unsaturated soils under low confining stresses.


Civil, Architectural and Environmental Engineering

Keywords and Phrases

Atmospheric pressure; Compression testing; Cost effectiveness; Highway engineering; Soils; Three dimensional computer graphics; Cost-effective methods; Deformation and strength; Low confining pressure; Pavement engineering; Stress-strain behaviors; Three-dimensional model; Unconfined compression; Unsaturated shear strength; Soil testing

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Article - Journal

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© 2015 National Research Council (U.S.), All rights reserved.

Publication Date

01 Nov 2015