Cut-Off Wall Integrity Evaluation Using Advanced Geophysical Imaging Technologies as Part of the Overall QA/QC Process: Herbert Hoover Dike Case Study

This rehabilitation project aimed to safeguard human life while mitigating the intolerable risk of detrimental social, economic, and environmental impacts in the area. The cutoff wall, a critical feature in the dike rehabilitation, is designed to mitigate any existing internal erosion, also referred to as "piping" and to prevent any further damage to the internal structure of a dike. To eliminate the hydraulic piping that is occurring through and under the embankment of the Herbert Hoover Dike (HHD or Dike) surrounding Lake Okeechobee in South Florida, the United States Army Corps Engineers (USACE) designed to install a partial cutoff wall using in situ soil mixed with cementitious materials. The typical process for evaluating the integrity of the cutoff wall was to obtain core samples of the cutoff wall for visual inspection, perform unconfined compressive strength tests, and to conduct in situ permeability testing. Recent advancements in geophysical technology specialty imaging have led USACE to adopt optical televiewer (OPTV) and closed-circuit television (CCTV) technology for inspecting the boreholes as an integral part of the QA/QC process. During inspection, the OPTV camera survey produced a high resolution 360° continuous detailed and oriented image of the borehole side walls. The CCTV camera survey provided a continuous downhole and side-view recording of the conditions of the borehole side walls. In this case study, the overall benefits and lessons learned through the use of geophysical imaging technology will be discussed in detail.