Nanaki YAMAMOTO

Experimental evaluation of tortuosity of porous media flow based on microscopic information

Yutaka FUKUMOTO

The flow in porous media, can be found in various types of materials treated in a wide range of research fields. In the civil engineering, the soil, rock, concrete, and asphalt used to build structures are the porous materials. Since the aging of such construction materials is closely related to the seepage flow, it is important from an engineering perspective to understand the fluid behavior in porous media in detail.
As one of the indicators for the evaluation of the characteristics of the seepage flow, tortuosity is often used. Tortuosity is an important indicator directly related to the value of hydraulic conductivity. With the development of three-dimensional and high-resolution computational fluid dynamics (CFD) methods for obtaining the details of flow paths and X-ray micro-computed tomography (micro-CT) methods for acquiring microstructures, methods for evaluating tortuosity have been investigated numerically or theoretically by many researchers. but few experimental evaluations have been conducted.
Almost all empirical equations for tortuosity are just a function of porosity and surface area and do not reflect information about local geometric structure. Construction materials sometimes have a layered structure, such as the boundary between embankment and foundation or road pavement. Near the boundary between layers with different pore properties, the permeability characteristics can change rapidly, leading to phenomena such as internal erosion. A better understanding of local infiltration characteristics could contribute to solving various aging degradation problems that occur in construction materials.
In this study, we focused on the hydraulic tortuosity which represents the tortuosity of the porous media flow, and the geometric tortuosity which represents the tortuosity of the porous media structure and investigated the effects of particle distribution conditions and Re on the porous media flow through experiments. As a result, a different trend from previous studies mainly based on numerical analysis was obtained at the boundary of the two-layer structure, indicating that hydraulic tortuosity may be affected by parameters such as particle arrangement and Re in addition to the filling ratio.