Variations in Atterberg Limits for the Lawton Clay with Acidic Pore Fluids

Abstract

The physical mechanisms that cause slope failure involving the Lawton Clay in the Puget Lowland have been well studied; however, the physio-chemical mechanisms, specifically acidic pore fluid are poorly understood. This study attempts to quantify the effect of pore fluid acidity on the Lawton Clay’s plasticity through Atterberg Limit tests. I conducted multiple runs of the liquid limit and plastic limit tests on rehydrated, homogenized samples of Lawton Clay with acidic solutions mimicking the composition of acid rain in the Seattle area at a pH range of 3.5 to 7. My results show a trend of increasing and then decreasing liquid limit with increasing acidity. This trend is best explained by changes in the thickness of the double diffuse layer and clay minerals’ ability to attract water to its surface. The changes in Atterberg Limits can be used as a proxy for changes in strength. The liquid limit results suggest that variations in pore fluid pH could affect the strength of the Lawton Clay and hence be an important variable in slope stability.