The Site-Specific Intervention Plan – An Indispensable Risk Reduction Tool for Dam Foundation Investigations in Challenging Conditions

During normal dam safety inspection activities, signs of potential internal erosion in the foundation of two dikes were detected downstream of the structures. As part of the remediation strategy, four large-scale geotechnical investigation programs were launched. Prevailing site conditions included the presence of above ground pore-water pressures and semi-pervious erodible soils. In this context, Site-Specific Intervention Plans (SSIP) were developed to mitigate the risk associated with performing intrusive geotechnical investigations in this particularly challenging setting.
The SSIPs were specifically adapted to different types of sensitive investigations to be conducted in critical areas. The SSIPs included a structured plan to mitigate potential critical situations, several Risk Reduction Measures and Rapid Response Procedures (RRP) adapted for each applicable hazard. On three occasions, Hydro-Québec had to apply the RRP to rectify problematic situations, with success on all occasions. This demonstrated that the SSIP is an indispensable tool for any site investigation program that could potentially affect the performance of a dam, especially in difficult foundation conditions.