Abstract:
The tensile strength of soil is often neglected. Because of the presence of matric suction,
unsaturated soils may have substantial tensile strengths with implications for a range of geotechnical
problems, such as slope stability, bearing capacity, and the integrity of clay liners.
Direct measurement of the tensile strength of soils is complex to carry out, while the simplicity
of the Brazilian tensile strength (BTS) test offers an attractive alternative. However, this
method was developed to measure the tensile strength of brittle materials. While suctionbound
unsaturated soils may behave in a brittle fashion at low moisture contents, such
materials become more ductile as the moisture content increases. This study investigated
the application of the BTS test to measure the tensile strength of unsaturated soil samples
over a range of moisture contents. Because of the low sample strength of these soils, the
use of curved loading platens is recommended. The required load angle depends on the ratio
between the compressive and tensile strength of the material tested. When brittle behavior is
obtained during testing, conventional interpretation may be used, i.e., the maximum mobilized
load during load application is used for tensile strength calculation. This is not appropriate
when testing ductile materials. During load application on ductile samples, the initial mobilized
load-deformation behavior is approximately linear and becomes nonlinear when tensile yielding
starts to occur, originating from the sample center where the full tensile strength is first
mobilized. It is recommended that, to obtain a conservative estimate of tensile strength, the
inflection point where behavior becomes nonlinear should be taken as representative of soil
tensile strength.
