Engineering geology of dam foundations in north - Western Greece

Abstract

The significance of the geological factors which controlled the formation of damsites, and the relationship between these factors and the soundness of foundation bedrock (mainly from the watertightness point of view) are studied in this work. The need to incorporate geotechnical design implications, in dam foundation studies, besides the geological descriptions which are involved in current classification schemes, is considered. The void volumes in the rock foundations of earth and rockfill dams, in three different geological environments in Greece, are assessed by the grout volumes spent in sealing off the dam rock foundations, and expressed as distinct grouting parameters. A prior assessment of the geological and the geotechnical records (up to the design stage) was made to isolate the geological factors governing the water tightness (permeability) characteristics of the three different foundation bedrocks. It was found that the dimensionless parameter "grout take per metre run per area of segment", as used in this study, has. particular attractions for assessing the pre-impounding water tightness of dam foundations. The relations of the bedrock discontinuity density distributions (as main grout absorbing elements) with the major geological factors involved in each site are discussed and their implications to the grouting results are pointed out. The geological environments of the Greek dams and the main geological factors pertaining to dam incidents have also been examined for comparison purposes, and for determining the degree of correlation for possible practical use in the design of future damsites.