The paper addresses the foundation stability analysis of two Swiss dams, namely Spitallamm arch-gravity dam (in the scope of a rehabilitation and heightening project) and lesToules arch dam (rehabilitation). The first example is actually in the design phase, with construction scheduled during the next decade, whilst the former one is currently under rehabilitation (2008–2011). The projects are reviewed with respect to the foundation stability conditions. The approach is similar in both cases: first the existing dam is back-analyzed, with emphasis on the foundation conditions, allowing the cross-checking of the design results with the available monitoring data (benchmarking). Based on that, the heightening and/or rehabilitation project is prepared and the most optimized solution in terms not only of safety but also of construction schedule and technology had been recommended.
In view of the rehabilitation or heightening of some existing dams, the initial project has to be retrieved from the archive (if ever available) and re-evaluated. Due to some specificities of the existing structure, in particular its behavior as monitored during its lifespan, but also with due consideration to the objectives of the rehabilitation or heightening and the interaction with the existing dam, these studies provide interesting and sometimes surprising outcomes. This is especially true considering the progress made in the past decades in the field of rock mechanics and foundation stability analyses, namely: – A better understanding of the rock mass behavior and the corresponding dam foundation aspects, which over the past decades have been more and more considered amongst the most critical issues of any dam project. This has been especially revealed following some terrific dam failures such as Malpasset arch dam occurred in 1959, involving the foundation dam failure. – The development of more sophisticated rock mass failure criteria in the 80s and 90 s.