Volume 2, Issue 3 (May 1974)
An Unconfined Direct Tension Test for Compacted Clays
Although problems associated with total stress tension arise in soil structures such as earth embankments and multilayer pavements, no standard tension test for soils exists. An unconfined direct tension test, either strain controlled or load controlled, is described, which can be used to determine the tensile (total) stress-strain characteristics of compacted clays. The overall tensile strains in the specimen are determined by observing the displacement of two surface markers spiked into the specimen with a displacement measuring optical device (DMOD) capable of measuring to one-micrometer displacement. An alternative radiographic technique of monitoring strains has shown that the distribution of average tensile strains in the specimens is substantially uniform. Moreover, the failure of the tension specimen occurs in midsection, indicating a uniaxial transmission of tensile force to the specimen. Comparison of standard triaxial unconfined compression tests with unconfined tension tests shows that elastic moduli are not equal in compression and tension for compacted clays at a given moisture content.