A Tensile Strength Apparatus with the Facility to Monitor Negative Pore-Water Pressure

Abstract

This article presents a new testing method for investigating the behavior of clayey geomaterials subjected to a tensile (negative) total stress. The method includes the use of high-capacity tensiometers to measure the pore–water pressure of the test specimen, an aspect which has not been demonstrated in any other direct tensile testing method. This addition allows interpretation of failure data in terms of effective stress rather than total stress, which is the approach that should be pursued in the saturated range. The test specimen shape and loading method have been modified from those commonly seen in existing literature to ensure that the direction of the major principal stress in the failure zone coincides with the direction of the externally applied tensile force, allowing for a more accurate analysis of tensile failure. Results are shown for saturated specimens and compared to results obtained for the same soil in uniaxial compression, using a modified version of the presented uniaxial tensile method, and a triaxial compression test. It is demonstrated that crack initiation occurs by shear failure if the data are interpreted in terms of effective stress rather than total stress and that the failure mechanisms under tension do not differ from compression.

Comparison of Test Methods for Determining the Tensile Strength of Soil and Weak Rocks

“…Flexure or bending tests are commonly used in many branches of civil engineering. In materials engineering, they are used for concrete and hard rock testing (Murray et al, 2019). The two most common flexure tests are the three-point and four-point bending tests.…”

“…A rectangular soil beam was placed on two support anvils and a concentrated downward force was applied to failure at midspan through the loading anvil. As the beam is bent, tensile and compressive stresses are respectively produced in the convex (outer) and concave (inner) sides of the specimen (Murray et al, 2019). Figure 4C shows the expected stress distribution over the cross section of a beam, where compressive stresses act above the neutral axis whilst tensile stresses act below it.…”