YIELDING OF MEXICO-CITY CLAY AND OTHER NATURAL CLAYS

Yielding is an important feature of the stress-strain behavior of lightly overconsolidated clays. This paper describes tests on 36-mm triaxial samples of natural Mexico City clay. The specimens are carefully trimmed, consolidated in increments along various stress paths to determine the yield-point characteristic curve of Mexico City clay. Once yielding is clearly defined, the specimens are subjected to an undrained compression at a constant strain rate. The clay exhibits marked changes in stiffness when it yields, and, thus, a well-defined yield envelope in stress space is obtained. This yield curve, together with other curves from the literature, gave information for natural clays with friction angles in normally consolidated range between 17.5-degrees and 45-degrees, allowing a generalization of the concept. The coefficient of earth pressure at rest in the normally consolidated range is also discussed. Data obtained on Mexico City clay show that the relationship proposed elsewhere is also valid for clays having a high friction angle.