Evaluating Turbulent Flow in Large Rockfill

This paper describes a laboratory testing program developed to assess the hydraulic properties of coarse rockfill by using a custom-built large-scale permeameter. Tests were performed by using samples 1.5 m in length and 0.7 m3 in volume. Knowing the hydraulic characteristics of coarse rockfill is important for assessing the safety of the structures under anticipated flow conditions in flow-through rockfill embankments. Flow in rockfill structures often departs from the laminar flow regime at typical operating flow conditions because of the characteristics of the rockfill materials. These characteristics include porosity, particle shape, particle size, roughness, and the tortuosity of the voids within the structure, which result in high velocities in large interconnected void spaces. For this reason, flow-through rockfill structures cannot be predicted by using Darcy’s law. The design and construction of a large-scale permeameter built at the University of Manitoba Hydraulic Research and Testing Facility is presented in detail. The experimental program, which used the large-scale permeameter, studied the nonlinear hydraulic characteristics of coarse rockfill materials for the coefficient in the power-law relationship between hydraulic gradient and bulk velocity. The results demonstrate that the large-scale permeameter successfully characterized the flow-through conditions of a variety of rockfill sizes and gradations under typical flow conditions. Results also allowed the determination of the coefficients to design flow-through rockfill dams for local rockfills.