Rock mass properties and their suitability as a foundation for a rolled compacted concrete gravity dam: case study of Beni Haroun dam (Mila, NE Algeria)

Abstract

Dams are generally designed and built to resist the most severe destabilizing conditions. Their failures have caused severe damages and loss of lives through history. The investigations carried out on failed dams have, in most cases, unveiled that foundation problems are usually the cause. These problems are very often related to the condition of discontinuities dissecting the rock foundations. Being weak, they are the preferred planes for deformation and rupture causing the collapse of the whole structure. This study deals with the rock mass properties and their suitability as rock foundation for Beni Haroun dam, the largest dam in Algeria. The dam is located in the north-eastern part of Algeria on Wadi El-Kebeir, approximately 40 km from its outfall in the Mediterranean Sea. The dam is a roller-compacted concrete type with a height of 120 m, a crest length of 710 m, and a water storage capacity of approximately 1 billion m3. The dam is founded on Ypresian limestone rock mass. The present study was carried out both in the field and in a laboratory. The field study included geological mapping of the engineering, an intensive discontinuity survey, and sampling. Laboratory tests were conducted to determine shear strength, uniaxial compressive strength, tensile strengths, and Young’s modulus of rock samples. The shear strength of discontinuity was evaluated according to the criterion developed by Barton and Choubey. The joint roughness coefficient was calculated through a statistical approach using the parameter Z2, and an empirical approach based on a visual comparison with standard profiles of the Barton–Choubey roughness. The quality of the rock mass was estimated using Rock Mass Rating (RMR) and Geological Strength Index (GSI) systems. The stability of the dam foundation was assessed using the DMR system and the Hoek and Brown failure criteria. The rock mass of the dam foundation is the Ypresian limestone formation and is of fair quality. This study has shown that this rock mass is adequate as foundation for Beni Haroun RCC dam.