Use of Free Ends in Triaxial Testing of Clays

by Laing Barden,
J. W. McDermott,

Serial Information: Journal of the Soil Mechanics and Foundations Division, 1965, Vol. 91, Issue 6, Pg. 1-24

Document Type: Journal Paper


The end restraint in the conventional triaxial test imposes nonuniformities of stress and deformation on the sample under test. In the undrained testing of clays, this results in the development of large pore pressure gradients—the pressure being measured at the base remote from the central failing zone—and this can cause serious errors, particularly in the deduced values of c' and ∖a/'. The object of the present work was to investigate the effectiveness of the simple lubricated end platens developed previously in drained triaxial tests on sand samples, thus providing uniform conditions in undrained tests on clay. Measurements of vertical and radial pore pressure gradients, internal moisture migration, and the deformed shapes of both fixed and free ended samples tested at various rates of strain proved conclusively that the simple free ends go a long way in providing uniform conditions in the triaxial test. Their use minimizes a number of important errors and permits shorter testing times in undrained tests with pore pressure measurement.

Subject Headings: Triaxial tests | Pore pressure | Soil pressure | Pressure measurement | Soil tests | Clays | Deformation (mechanics) | Errors (statistics)

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