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Uniaxial Tensile Test for Soil.
Final rept. Jan 81-Aug 84,
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS GEOTECHNICAL LAB
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There are a number of applications where even a small amount of tensile strength can have significant influence on computational results and actual structure performance -- e.g. the tensile strengths of clays are significant in problems involving low mean normal stresses. Motivation for studying tensile strength comes indirectly from the study of partially saturated soils, as the tensile strength is presumably derived from the suction potential of the soil. This report describes an apparatus for measuring strength of soil in direct tension. Data are presented for compacted Vicksburg silty clay for uniaxial tension and unconsolidated undrained Q compression tests with a view toward proposing criteria to relate tensile and compressive strengths for partially saturated materials. The primary advantage of the apparatus is its ability to apply a uniaxial load through precisely aligned end-grips, which are restricted from rotations about the long axis of the specimen. This design is in contrast to tensile tests for rock and concrete that avoid applying moments to specimen ends by attaching the end-grips to a flexible pulling mechanism. A flexible loading mechanism was viewed as unsuitable for brittle low-strength compacted soils because of difficulties in achieving precise loading alignment. Precise alignment for the tensile device is achieved by mounting one of the end-grips on a commercially available slide table that restricts movement to one direction. A major finding of the laboratory investigation was that of all methods used to determine tensile properties, the highest strength and stiffness was obtained from the direct tensile device.
APPROVED FOR PUBLIC RELEASE