Wedge Instability on the Abutment of a Gravity Dam in Italy

Abstract

This paper describes a wedge instability occurred during excavation of the right abutment slope in a granite rock mass at the Cumbidanovu dam site in Italy. The dam is a 72.7 m high concrete gravity dam, presently under construction. The slopes are characterized by the presence of a granite rock mass, rather complex geologic features (shear/fault zones), multiple rock joint sets, and significant differences in rock mass quality. The rock mass conditions are briefly illustrated based on systematic geological and discontinuity mapping during excavation of the abutment slopes, from the top down. Also briefly described are the rock mass characterization studies, including the results of laboratory and in situ testing. The results of three-dimensional stability studies with limit equilibrium and finite element analyses are illustrated. The main purpose has been to back-analyze the rock wedge instability based on the available data and the geological mapping performed, in view of the stabilization measures to be adopted, including a reshaping of the abutment slope.