Geotechnical and geophysical investigations for a dam safety project Amer Awad, Dhiraj Karki, Alastair McClymont, Allen Xu, Max Layton Advisian, Calgary, Alberta, Canada ABSTRACT Advisian was retained to undertake a dam safety review (DSR) for a client. The facility was constructed in the 1970’s and very limited technical and background information was available for the facility. As such, geophysical and geotechnical investigations were carried out for the facility, including the installation of 10 vibrating wire piezometers and one slope inclinometer. Data interpreted from the two investigations were utilized to complete the dam modelling and assessment. The DSR activities followed the 2013 CDA Guidelines. Two separate DSR reports where submitted to the client, namely a report related to the liquefaction and risk analyses and a report for all the other activities. This paper discusses the geotechnical and geophysical investigations findings and sheds light on the lessons learnt from the investigations and the finding of the DSR. RÉSUMÉ Advisian a été retenu pour entreprendre un examen de la sécurité des barrages (DSR) pour un client. L’installation a été construite dans les années 1970 et des renseignements techniques et de base très limitée étaient disponibles pour l’installation. À ce titre, des recherches géophysiques et géotechniques ont été effectuées pour l’installation, y compris l’installation de 10 piézomètres vibrants et d’un inclinomètre de pente. Les données interprétées à partir des deux enquêtes ont été utilisées pour compléter la modélisation et l’évaluation du barrage. Les activités du DSR ont suivi les Lignes directrices de l’ADC de 2013. Deux rapports DSR distincts que nous avons soumis au client, à savoir un rapport relatif aux analyses de liquéfaction et de risque et un rapport pour toutes les autres activités. Cet article traite des résultats des enquêtes géotechniques et géophysiques et met en lumière les leçons tirées des enquêtes et de la constatation du DSR. 1 INTRODUCTION Advisian was retained to undertake a dam safety review (DSR) for a client. The facility was constructed in the 1970’s and very limited technical and background information was available for the facility. Further, no previous DSR was completed for the facility since it was constructed in the early 1970’s and no geotechnical data required to complete the DSR were available. Consequently, Advisian recommended geotechnical and geophysical investigations to capture the necessary data to complete the DSR for the dam. The geotechnical investigation included advancement of seven (7) boreholes through the dam fill into the foundation material, with depths ranging from 11 to 20 meters (m) below ground surface. The geotechnical field program also included the installation of 10 vibrating wire piezometers in six (6) boreholes and one slope inclinometer casing in the seventh borehole. To obtain provide supplementary information on the internal dam structure and the underlying native material between boreholes, a geophysical investigation was completed using electrical resistivity tomography (ERT), multichannel analysis of surface waves (MASW) and seismic refraction methods, along 4 lines spanning 120 m to 240 m long (Figure 1). Data interpreted from the two investigations were utilized to complete the dam modelling and assessment. The DSR activities followed the 2013 CDA Guidelines. Two separate DSR reports we submitted to the client, namely a report related to the liquefaction and risk analyses and a report for all the other activities. This paper discusses the geotechnical and geophysical investigations findings and sheds light on the lessons learnt from the investigations and the finding of the DSR. 2 GEOPHYSICAL INVESTIGATION 2.1 Geophysical Methodology Electrical resistivity tomography (ERT) is a technique for mapping the distribution of subsurface electrical resistivity (or its inverse conductivity) in a cross-sectional format. Resistivity data are collected through a linear