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Publication Date

September 2007


The geologic setting of Mosul Dam is critically important for its engineering implications and its usefulness and contribution to engineer- ing and operational decisions about the dam. The dam was constructed on alternating and highly variable units of gypsum, anhydrite, marl, and lime- stone, each of which is soluble in water under the environmental and hydrogeologic conditions of the dam. From a geologic standpoint, the foundation is very poor, and the site geology is the principal cause of con- tinuing intense concern about the safety of the structure. Mineralogic variability within rock units resulted from original depositional processes that created interfaces and zones of weakness within individual beds. These natural zones of weakness now function as ingress points for seep water and allow dissolution zones to move vertically and horizontally. Dissolution is occurring at a faster rate than natural geologic processes. Sinkholes that have reached the surface recently on the east abutment indicate large-scale dissolution in the subsurface. Rock quality, grout- curtain efficiency as related to piezometer data, sinkhole development, sinkhole retreatment, dissolution rates of rock material, and water chemis- try (total dissolved solids) collectively indicate that the dissolution front is moving to the east and downstream. The rate of subsurface dissolution has been increased by the presence of the reservoir. The pattern of regrouting in and between recently grouted sections of the dam shows that grouting at one location causes the flow path (seepage) of subsurface water to move to another location, but does not stop the seepage. At or above a pool depth of 318 m above sea level, the rate of subsurface dissolution increases markedly, leading to the recommendation that the pool not be raised above 318 m.


Geologic Conceptual Model, Mosul Dam, Engineering Implications, Geologic Settings

Document Type



Engineer Research and Development Center, Vol. TR-07-10 (2007-09).





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