Unsaturated and Transient Seepage Analysis of San Luis Dam

This paper uses the San Luis Dam upstream slide to evaluate the pore-water pressures at failure and progression of the phreatic surface through the fine-grained core for drawdown stability analyses. The hydraulic conductivity and compressibility parameters of saturated and unsaturated soils are calibrated using the reservoir hydrograph and 13 piezometers in order to evaluate the pore-water pressures at failure. The analyses show unsaturated and transient seepage analyses can be used to estimate pore-water pressures during drawdown for various stability analyses and evaluate the progression of the phreatic surface through the fine-grained core. The transient results also indicate the van Genuchten parameter significantly influences unsaturated soil response during drawdown. Different meshing techniques can produce consistent moisture content profiles in two different seepage software packages, but in situ measurement of moisture content and suction pressure is recommended to develop an unsaturated and transient seepage model.