Pore pressure response in the uppermost part of a clay soil slope - Two case studies in the Gothenburg region
In this research project the pore pressures in the uppermost 5 to 10 meters of clayey soils in southwestern Sweden are studied. The focus is on natural, short time variations, such as yearly variations due to precipitation, frost and evaporation. The long term benefit with the study is the ability to make better and more reliable predictions of pore pressure variations in clay slopes and thereby improving the reliability of the stability analyses. Field measurements have been performed at two sites in the greater Gothenburg area. In total 35 piezometers were installed in three slopes and they were monitored during 1.5 to 3 years. Installation depths varied between 0.5 to 49 meters, with a majority of the piezometers installed at depths less than 5 meters. The correlation between the measured pore pressures and precipitation was studied. Simulations with the computer software SEEP/W were performed in order to investigate how well the pore pressure regime in a slope can be predicted. Results from the simulations are compared with measured values, with special focus on the uppermost 5 to 10 meters. Three types of prediction levels are defined, depending on how detailed information is needed. Recommendations are given for a methodology that the practicing engineer can use when faced with the task to measure and predict the design pore pressure.