Stability of concrete macro-roughness linings for overflow protection of earth embankment dams

Abstract

A macro-roughness lining system for the protection of earth embankment dams during overflow is presented. It consists of precast concrete elements placed on a drainage-separation layer. The main difference between this system and other existing concrete element systems is the stability concept, based on the self-weight of the blocks. Several types of elements were developed and tested in a physical model for a typical dam slope of 1V:3H. Failure conditions were identified after submitting the elements to increasing flow discharges. Furthermore, different foundation drainage and shear conditions between the elements and their foundation and different joint alignments were studied. Flow characteristics were observed and measured for quasi-uniform flow conditions. Based on the experimental results, a stability model was developed to compute the design safety factor. The model is based on the governing overturning equation (predominant failure mechanism) and on assumptions concerning the acting hydrodynamic forces, the hydrostatic uplift, and the concentration of air in the flow. Synoptic design charts were derived for 1V:3H dam slopes, allowing the rapid estimate of the lining characteristics as dimensions and weight for a certain withstood design unit discharge, for various margins of safety. The developed macro-roughness lining system is envisaged for the spillway rehabilitation of existing dams, but also for the design and construction of spillways of low dams (up to 30 m in height) and for the protection of overflow cofferdams.Key words: overflow dams, erosion protection, linings, macro-roughness, stability, drainage and spillways.