Relative and interactive effects of fluid's physicochemical characteristics on the incipient motion of a granular particle under laminar flow condition

This paper presents an experimental research for studying the relative and interactive effects of three physicochemical fluid characteristics (viscosity, pH, and ionic strength) on the incipient motion of a granular particle under laminar flow condition. Critical flow velocity for particle's incipient motion, an important factor for evaluating flow-induced soil erosion, was used to quantify the relative erosive capacity of the test fluids. Response surface methodology (RSM), a statistical design of experiments, was used to design and implement 20 test fluids with various levels of the three fluid characteristics. Incipient motion of a highly spherical glass bead positioned atop a specially designed and manufactured support pocket within an enclosed flow cell was observed using a microscope video camera. The critical flow velocity was quantified for seven repeat trials for each of the 20 test fluids. Regression analyses were conducted on the results to generate a statistical model to describe the relative effects of the three factors and their interactions. The main findings include: (1) viscosity, pH, and their two-way interaction were determined to be the most influencing factors on critical velocity; (2) the effects of the three fluid characteristics on critical velocity follow the following decreasing order: viscosity, pH, and ionic strength; (3) viscosity and pH were both shown to have an inverse relationship with critical velocity; and (4) at higher pH (such as 10.5), the viscosity has greater influence on critical velocity than at a lower pH (such as 3.5).