Application of a Cyclic Degradation Model for Pore Pressure Accumulation in Loose Sands and Silts Subjected to Dynamic Loading

Abstract

Most cyclic soil models which are used to estimate strain and pore pressure accumulations, are soil specific and, often evaluate the accumulation model either as a function of the number of load cycles or they tend to utilize parameters which can only be obtained by using detailed laboratory tests. This paper attempts to enhance the capabilities of a simple plasticity model which can approximate the trend of pore pressure accumulation. This function uses a stress dependent degradation parameter which allows the yield loci to adjust and reduce its size at the end of each load cycle. The cyclic degradation model which was originally developed for clays, was adapted for sands and silts in this work with the use of two new parameters. The model was tested by using the cyclic triaxial data of three non-plastic soils. These samples were subjected to cyclic load amplitudes which are normally used in most seismic studies. The modified degradation model could predict fairly well the pore pressure accumulation in high-load amplitude tests but lead to over-prediction in low-load amplitude tests, unless the function was allowed to taper off at large cycles. Notwithstanding the above, the above cyclic model using the degraded yield surface, was incapable of correctly predicting the stress paths which were close to the sample’s ultimate state as it failed to permit phase transformation which is generally observed in sands and silts.