Effect of cyclic confining pressure on excess pore water pressure variation inside granule-clay mixtures

This study investigates the results of experimental and numerical studies on effect of Variable Confining Pressure (VCP) on Excess Pore Water Pressure (EPWP) increase in granule-clay mixtures. EPWP plays an important role in the seismic stability of the dams constructed with a core of granule-clay mixture. These dams would experience VCP during an earthquake. This is unlike the previous studies on the material behaviour which only included Constant Confining Pressure (CCP). VCP experiments showed that EPWP increases in the granule-clay mixture compared with the pure clay which agrees with the CCP-based literature in this regard. By comparison of experiments and numerical models, it was shown that the pore pressure build-up between the grains in a granule-clay mixture can be numerically modelled by just modelling two adjacent grains. Numerical models showed that EPWP decreases with an increase in granule size, and increases with an increase in granule content. However, the amount of EPWP increase in a mixture compared to the pure clay is higher in CCP loading, compared with the VCP loading. It means the rate of EPWP build-up in the mixed and pure clay get closer in a VCP loading, compared to the CCP loading.