Subsurface Investigation of a Major dam Founded in Karstic Terrain Vargas Juan1, Chowdhury Khaled2, Millet Richard3, Malyala Nagesh4 1Vice President, AECOM, Dallas, Texas, USA 2Senior Geotechnical Engineer, USACE, Sacramento, California, USA 3Vice President, AECOM, Sacramento, California, USA 4Technical Leader, AECOM, Sacramento, California, USA Online published on 16 April, 2022. Abstract This paper describes the intrusive and non-intrusive exploration methods used during the subsurface investigation of a major dam in southern United States. The Dam is located on a karstic foundation. The dam leaks a significant volume of water. Numerous sinkholes have formed in the upstream side of the dam in the last several decades, which were repaired locally. The Dam has been assigned a Dam Safety Action Classification (DSAC)-II Potentially Unsafe rating. The investigation was performed in support of the Dam Safety Modification Study (DSMS) conducted for the Dam. The paper presents how multiple investigation techniques were used to identify anomalies, corroborate previous findings, validate and calibrate information and develop a 3D geological model of the site. The field investigation included surface geophysics, downhole geophysics, soil borings, test pits, piezometers, dye tracing study, and installation of an extensive automated monitoring system. The geophysical study for the project included techniques such as microgravity, electrical resistivity imaging survey, and MASW. The 3D geological model of the site incorporates historical and recent site information. The model is a practical tool to visualize data, identify potential flow paths and help develop remedial measures. Top |