Stabilized-coupled modelling of creep phenomena for saturated porous media

The proposal of two models for simulating the behaviour of soils subjected to secondary consolidation (creep) is here described. In normal circumstances, settlements due to secondary consolidation account for only a small fraction of the total settlements, having a magnitude of a small percentage of the primary consolidation settlements due to compression. However, in a situation where very soft organic clays are under compression, secondary consolidation may be a much more important factor. The models are implemented in a fully coupled finite element code where the governing equations are discretized in time in accordance to what proposed by the characteristic-based split method, well known in Fluid Mechanics, obtaining a stabilizing split-type method. In this way, pressure oscillations (wiggles) - usually present in consolidation problems - have been eliminated. The first model assumes that the soil skeleton consists of a linear spring in series with a Kelvin body: the spring is representative of an elastic model, whereas the Kelvin body keeps count of a time-progressing strain, once the primary consolidation has stopped. The second model considers some Maxwell chains in parallel. Their efficiency is proved studying the long-term behaviour of soft soils; the results, compared with in situ measurements, show a good accuracy in predicting creep phenomena for soils.