Numerical Modeling of Cyclic Loading on Clay

Abstract

Soil`s behavior, when subjected to cyclic loading, may often be reduced stiffness giving large deformations. For undrained conditions a possible pore pressure build-up will reduce the capacity even further. This may affect the design of foundations and the stability of slopes.Undrained cyclic response of clay has been simulated by an Iwan model combining several elasto-plastic soil models coupled in parallel. Each of these models was assigned with a unique set of parameters. The soil behavior is described by the Cam Clay Model, with a degradation term implemented. The cyclic model is independent of the frequency of the applied load. Seven triaxial tests have been conducted, where five of these were cyclic tests with different cyclic amplitudes. High friction forces were found to disturb the quality of the cyclic tests. In addition one creep test, and one shear test was conducted. The results from the cyclic simulation is totally dependent on the number and values of the parameters used. The interaction between them will also influence the results. Manually determination of the parameters needed are a time-consuming process. A recommended solution to improve the model is to find an automatic method where the parameters could be determined from a representative cyclic triaxial test.Based on the most common results from the triaxial simulations, a realistic pore pressure build-up may be modeled. Hysteresis in the soil will also be accounted for. However, low accumulation of plastic strains and only a slight change in stiffness resulted in approximate identical hysteresis loops calculated for each cycle. The reason for this is most likely that the right value, number and interaction between the included parameters have to be found. There are some unsolved issues regarding modeling of the permanent strain that have to further be evaluated. By solving these problems, the presented method for modeling undrained cyclic loading on clay is likely to be representative for the general trend of the soil`s behavior.