Determination of Nonlinear Head Loss Equation of Flow through Rockfill by One-dimensional Column Tests

Abstract

Use of local materials is not economically justifiable but also has secondary benefits such as improved self help in developing countries. Typical application of the local material can be found in throughflow embankments constructed by using rockfill materials to reduce peak flow of flood water. In designing the throughflow dam, it is necessary to evaluate the ability of rockfill to transmit water in response to an applied flow gradient.
As the first phase of our study to develop a design procedure for the throughflow dam, onedimensional permeability tests of the rock column specimen were carried out to investigate a head loss behavior of flow through rockfill disposition. A power-type head loss equation was proposed based on a relationship between friction factor and Reynolds number, and coefficients describing the head loss equation were determined as a function of the hydraulic mean radius. One of practical features of the head loss equation proposed is that it includes a hydraulic mean radius which can characterize effects of particle size, shape and disposition of rockfill on the hydraulic behavior of flow through granular materials. Determining the hydraulic mean radius, one can predict easily flow rate through rockfill in response to the applied hydraulic gradient by using the proposed equation. A method to determine the hydraulic mean radius based on Zingg classification of rock particle shape and the published data was proposed. It was shown that the velocity in voids calculated by the head loss equation proposed agrees fairly well with the one calculated by the Wilkins' equation which has been considered as the one most commonly used in practice. Small remarks on subjects to be investigated in our study was commented lastly.