Determination of Flow Parameters in Layered Rockfill Media Using Tracer Technique

Abstract

The present paper aims to develop improved models for predicting flow behavior, accounting for factors such as layer properties, grain size distributions, and transition zones between layers. Mathematical equations, including the Forchheimer equation and modified Darcy-Weisbach friction factor, are derived for characterizing non-Darcy flow in layered porous media. Empirical investigations employed using a laboratory flume with four layers of rockfill material arranged from coarse to fine, with particle diameters of 3.1, 1.8, 1.1, and 0.8 cm. Tracer injection techniques were used to study pore flow velocities, with electrical conductivity sensors capturing breakthrough curves. The effects of varying tracer mass and discharge rates on peak arrival times and flow profiles were analyzed. Key findings include the oscillatory behavior of flow depth, hydraulic gradient, head loss, and friction factor profiles at layer interfaces, particularly at higher discharge rates. These discontinuities highlight the influence of layer transitions and heterogeneities on flow dynamics. Additionally, higher discharge rates resulted in faster tracer transport, indicating less dispersion at higher velocities. The experimental data revealed linear relationships between hydraulic gradients and intrinsic velocities, with decreasing slopes for smaller particle sizes, reflecting reduced hydraulic conductivity. The study provides insights into modeling techniques that incorporate layer properties, grain size variations, and transition zones.

Keywords

• layered rockfill media
• flow parameters
• equivalent hydraulic conductivity
• tracer technique