Defects in Foundation Design Due to Miss-Interpretation of the Geological Data: A Case Study of Mosul Dam

Abstract

Existing engineering problems in Mosul Dam and their background are discussed in this paper. A thorough review of the available geological reports was made. These reports covered many decades of investigations from 1953 up to the investigations performed during the construction of the dam. A large volume of geological information was accumulated during these investigations, but it is unfortunate to see that some of the basic facts were not interpreted correctly. This applies to the incorrect correlation of the encountered beds in the exploration boreholes and miss-understanding of the actual stratigraphic succession at the dam site. This misinterpretation contributed to misleading results regarding the true karst zones and the type of rocks and their thicknesses in the foundation zone and surrounding area. As a result, the dam was placed on problematic foundations consisting of brecciated and highly kartsified gypsum/anhydrite rocks and/or conglomerates in which gypsum forms the main constituent as cementing materials. Karstified beds were not recognized in some depths and were described as normal marl and/or breccias. This also added to the use of improper method of foundation treatment by adopting a deep grout curtain as the main anti-seepage measure instead of using a more positive measure by constructing a diaphragm wall. The mentioned misinterpretations are discussed here in details together with their consequences, and a more accurate picture of the geology is presented.