Inferring apparent Newtonian viscosities of liquefied soils from physical models – Analysis using computational fluid dynamics

The behavior of liquefied soil can be simply portrayed as a viscous fluid through a single parameter viscosity. Physical modeling has often been used to estimate apparent Newtonian viscosities of liquefied soils. In these experiments, objects (e.g., spheres, cylinders, plates) are dragged through liquefied soils and the measured drag forces are analyzed using analytical, closed form solutions to determine the apparent Newtonian viscosities of the liquefied soils considered to behave as Newtonian fluid. This paper presents computational fluid dynamics (CFD)-based 2D and 3D analyses of some typical 1g and centrifuge physical models found in the literature that included dragged 3D objects (cylinder, plate, and sphere) through liquefied soils. The simulations revealed that the apparent Newtonian viscosity predicted through 3D CFD analysis simulating a sphere dragged through liquefied soil matched well with that predicted using the Stokes analytical solution, as both the CFD and analytical solution captured the 3D nature of the fluid flow around the sphere. However, the apparent Newtonian viscosities based on 2D analytical solutions applied to physical modeling results of a cylinder and a plate were found to be three to five times greater than those when 3D effects were considered in the 3D CFD simulations. The analyses showed that applying 2D assumption to 3D flow of liquefied soils could lead to unconservative estimates of apparent Newtonian viscosities as the true 3D nature of the flow of liquefied soil is not adequately captured in 2D solutions.