Finite element analysis of the non-uniform behavior of structured clay under shear

Conventional triaxial tests are widely used to interpret the stress-strain behavior of soils. The non-uniformity of their stress-strain relationship and the localization of deformation normally occur during shear test and affect the observed test results. This article investigates the non-uniform behavior of artificially structured (i.e., cemented) specimens experiencing shear due to an end restraint under various testing conditions. The conditions investigated include the stress state, the drainage conditions, and the strength improvement associated with the cementation effect. A finite element analysis has been performed using the Modified Structured Cam Clay (MSCC) model, which was developed as a generalized constitutive model for destructured, naturally structured, and artificially structured clays. The shear behavior of artificially structured cylindrical specimens was simulated under both drained and undrained shearing by a coupled hydro-mechanical finite element analysis. The stress-strain distributions and the local stress-strain relations of the artificially structured specimens are compared with those of the destructured specimens. It is evident that the end restraint significantly influences the shear response in drained conditions, particularly for the tests with a high yield stress ratio (YSRiso, which is the ratio of the yield stress to the current stress) and a highly cemented structure. The non-uniform stress-strain behavior is attributed to the non-uniform lateral deformation, which results in a variation in stress paths for different points within the specimen. The different effective stress paths for different points within the specimen affect the overall performance of the specimen, including the yield stresses, the yield strengths and the destructuring processes for a structured specimen. The specimens experiencing shear with high confinement in a Normally Consolidated (NC) state deform relatively uniformly, while those with low confinement in an Over-Consolidated (OC) state display a non-uniform lateral deformation. Hence, the destructured and structured NC specimens exhibit more uniform stress-strain behavior than the OC specimens. The highly structured specimens show more nonuniform stress-strain behavior than the destructured specimens. In conclusion, the end restraint plays significant role in the specimen deformation for both destructured and structured specimens. Special care should be taken for destructured specimens in an overconsolidated state, and for structured specimens in both normally and over-consolidated states.

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