USACE has completed the last of all planned risk reduction measures at Herbert Hoover Dike (HHD) to address actionable potential failure modes (PFM) related to embankment and foundation seepage, deteriorating culverts, and potential overtopping. HHD is a 143-mile-long earthen embankment that surrounds Lake Okeechobee in south Florida. Originally constructed as a series of muck dikes by local agricultural interests (early 1900s), construction via hydraulic fill techniques began in the 1930s with expansion and raising in the 1960s. No systematic compaction efforts were evident in either era of construction. No measures were included to prevent failure by seepage and piping. In 2006 USACE classified select portions of HHD Dam Safety Action Class (DSAC) I due to the urgency of repairs needed and high likelihood of failure from seepage and piping. In addition, 32 federal culverts penetrate the HHD system. Construction of culverts occurred in the both the 1930s and 1960s eras. Deterioration and poor construction practices rendered the culverts an immediate and significant risk of failure due to the loss of embankment material into and along the culverts. In 2011 USACE was authorized to replace or remove 32 culverts that posed unacceptable risks due to the high probability of failure. HHD is also subject to tropical cyclone wind induced storm surge and waves. Overtopping was identified as a credible failure mode at isolated low spots. In 2016 USACE was authorized to armor the embankment. To address seepage concerns, more than 56 miles of soil-cement-bentonite (SCB) cutoff wall were installed. Multiple construction methods were used including cutter-soil-mixer (CSM), trench cutting and re-mixing deep (TRD), hydromill and clamshell, and single fluid jet grouting. To address the deteriorating culverts, 28 of the 32 culverts were replaced that incorporated seepage control features in accordance with best practices. Lastly, embankment low points subject to overtopping were armored with articulating concrete block mattress (ACBM) and riprap revetements. By 2023 the implemented risk reduction measures successfully reduced risks below tolerable levels and the select portions were re-classified with DSAC 4 ratings (Low Incremental Risk). This paper presents a brief overview of the geotechnical solutions used to achieve the risk reductions.
