Sedimentation Behavior of Clays in Response to Pore-Fluid Chemistry: Effect of Ionic Concentration and pH on Its Trends

Abstract

This study investigates the effect of pore fluid chemistry on the sedimentation trends and liquid and plastic limits within the new fines classification framework for four clayey soils with different specific surface and mineralogy. The sedimentation tests and fall cone tests are performed with seven different ionic concentrations (c = 1 × 10−5 ∼ 1.8 M) and the four target pH values (pH = 3, 5, 7, and 9) for each of the ionic concentrations. Three different sedimentation trends such as flocculated, dispersed, and mixed (at c = 0.0015-to-0.003 M) modes are observed at different ion concentrations and pH conditions of the pore fluids. Three sedimentation parameters named A1, A2 and A3 are defined from the sedimentation curve. The relationship between them implies the salient features of the sedimentation trend for tested clayey soils. These parameters confirm the observed sedimentation modes and the critical ionic concentration; c* ∼ 3 × 10−3 M for AMK and EPK (high specific surface) and c* ∼ 1.5 × 10−3 M for LKW and MI (low specific surface) where notable fabric change occurs. The higher specific surface clays are classified as intermediate electrical sensitive clays whereas the lower specific surface clays are categorized into low electrical sensitivity fines in the new classification chart. A complementary data analysis for the sedimentation parameters and the new fines classification chart reveals that the robust link between distinct sedimentation trends and salient features of clay particles captured in the new fines classification chart can be useful to predict the sedimentation modes of clays with different pore fluid chemistry.