Fruitgrowers Dam’s Left Abutment Landslide Evaluation

This is a case study of Fruitgrowers Dam, which is an earthfill embankment constructed in western Colorado in 1938-1939. The left abutment of the dam was constructed on an active block landslide founded in the Mancos Shale. Movement of the landslide has been documented since construction and represents a potential risk to the performance of the dam. An extensive instrumentation monitoring program was initiated in 1987 due to movements of the landslide. The risk presented to the dam by the landslide was evaluated in 2014. In order to define the risks, instrumentation data were used to define the landslide extent, movement directions, and movement rates, and laboratory testing and back analyses were used to evaluate the material shear strengths of the slide plane. The results of these analyses were used to develop and evaluate potential failure modes related to the landslide movement and to assess the risk to the dam.