Experimental investigation of stress-strain characteristics of clays under repeated loading



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Dynamic triaxial tests are described in which repeated stress cycles were applied to fabricated specimens and to natural samples of clay. General considerations of dynamic triaxial testing of soils are reviewed and the results of a series of such tests are reported. Repeated loading tests indicated that the deformation of normally consolidated and overconsolidated clay specimens depended on the number of stress applications and was independent of the frequency of the stress applications. As the number of stress applications increased, the stress-strain loop and nonrecoverable deformations were larger. For natural clay samples, the greater the plasticity index or liquidity index, the larger were the deformations occurring at the same condition. Stress-strain-pore water pressure variations were dependent on the level of repeated stress. It was found that, for any particular consolidation history, a critical level of repeated stress existed, below which a state of nonfailure equilibrium was reached where the effective stress path curves formed closed hysteresis loops. An interesting feature of the test results was that a linear relationship between the magnitude of the repeated stress and the increase in pore water pressure existed for stress levels below the critical value. The values of pore water pressure coefficient A were calculated at a certain repeated stress level.