Constant Water Content Compression Tests on Unsaturated Compacted Soil with Suction Measurement Using a HCT

Abstract

Soil compaction is a process used in different engineering works; from the most complex to the simplest, the quality of soil compaction indiscriminately affects the final condition of the compacted soil in terms of engineering projects. Moreover, aspects such as time of construction and cost are extremely important in works that require compacted soils, particularly because of the climate in tropical regions. In these regions, the abundance of residual soils makes this material a preferential candidate for use in engineering projects. Considering that most compacted soils will remain in an unsaturated condition, it is extremely important to study and to characterize these materials, not only in the saturated condition, but also in an unsaturated state. Within this context, this study analyzes the shear strength behavior of a compacted residual soil of gneiss, collected in two sampling campaigns from an area located at the experimental site of the University of São Paulo in São Paulo, Brazil. The focus lies in determining the surface failure envelope for this soil by conducting several triaxial compression tests under saturated and unsaturated conditions. The interpretation of the results is discussed based on the use of the data obtained with the specimen in a saturated state. Thirty-six triaxial tests were performed, 18 of them with direct suction measurement using a high-capacity tensiometer (HCT). Results demonstrated the advantages of the constant water content tests (CWs) with the use of a HCT, such as their simplicity and reduced testing time for obtaining the surface failure envelope.