This paper presents the soil’s internal erosion in earthen embankments due to seepage with various physicochemical fluid characteristics and flow conditions. The paper includes two components: (1) experimental study on the relative and interactive effects of fluid’s viscosity, pH, and ionic strength on the incipient motion of a single granular particle under laminar flow condition, and (2) bench-scale piping erosion progression of sand considering the same seepage’s physicochemical characteristics under turbulent flow. An innovative experimental setup was designed and constructed that can simultaneously adjust fluid’s viscosity, pH, and ionic strength and provide repeatable test results on particle’s incipient motion and soil erosion rate index. This research showed the relative and interactive effects of three physicochemical characteristics (viscosity, pH and ionic strength) of permeating fluid on particle mobilization and on piping erosion of a sandy soil. This paper suggests in the field evaluation of piping in earthen embankments, if the subsurface seepage is known to possess different physicochemical characteristics from those of tap water or distilled water, the fluid’s properties should be considered in the laboratory tests of piping.