Endochronic modeling of cyclic response of sand

The nonlinear response of sand under cyclic loading and generation of pore-water pressure under undrained condition imparts complexity in modeling the cyclic response of sand. The generation and dissipation of pore pressure necessitates modeling more realistically the response of sand as a two phase system. Coupled models that capture the nonlinear response and pore pressure generation are rather limited. The behavior of sand strongly depends on its initial state and structure. In the present study a new pseudo coupled constitutive model based on the endochronic theory is developed. In the endochronic theory, the stress is defi ned a function of strain history with respect to an intrinsic time scale that depends on the material property in hand. The nonlinear undrained response of sand under cyclic loading is simulated based on the endochronic theory derived using the new intrinsic time scale coupled to a pore pressure generation mechanism that depends on the drained volumetric response of sand. A strain-rate sensitive plasticity model is used to simulate the cyclic response of sand based on the static triaxial test data. A visual C ++ code was written incorporating the proposed constitutive relationship and is integrated into the 3D fi nite difference code FLAC3D using the CPPUDM module to simulate the cyclic triaxial response of sand. The simulated cyclic triaxial response is compared with the published experimental cyclic triaxial tests on Nevada Sand. It is found that the developed model is able to capture the onset of cyclic liquefaction and its failure well. The proposed endochronic model is computationally simple and utilizes simple parameters obtained from the static stress-strain response and can be easily incorporated into any Finite Element or Finite Difference codes to capture more accurately the complex phenomenon of liquefaction of sand under cyclic loading conditions.