Cutoff Wall Construction by the Self-Hardening Slurry Method at the Herbert Hoover Dike, FL

The 140 mile long Herbert Hoover Dike (HHD) around Lake Okeechobee, FL, does not meet current dam safety criteria. The earthen embankment of the dike is subject to potential failure because of internal erosion, piping and slope instability at high water levels. Should the dike fail, there could be catastrophic effects on the entire southern Florida region. In 2007, the US Army Corp of Engineers placed the HHD on the Top 6 list of dams in the nation needing repair and has prioritized and budgeted more funding for HHD than any other dam safety construction project in the nation. In August 2007, TREVIICOS South (TIS) was one of three specialty contractors awarded an Indefinite Delivery Indefinite Quantity Contract for the construction of the cutoff wall through the dike and its foundation in the most vulnerable section specified as Reach 1, which extends from Belle Glade to Port Mayaca, FL, for a total of about 22 miles. In June 2008, the USACE awarded TIS a Multiple Task Order Contract, Task Order No. 3, which included the installation of a 500 ft long cutoff wall test section and options to construct an additional 16,200 ft long cutoff wall. TIS selected the self-hardening slurry method for the cutoff wall. The excavation is performed through the soil with mechanical and hydraulic clamshells, and in the limestone rock with a hydromill cutter, to a depth of up to 80 ft from the top of the dike. During excavation, the slurry maintains the trench stability. At the completion of the excavation, the slurry hardens and becomes the wall backfill material. Within 28 days from the installation, the cutoff wall is cored approximately every 200 ft and tested for acceptance. Testing includes the measurement of unconfined compressive strength, as well as triaxial and in-situ permeability. In April 2009, following the approval of the test section, TIS began the installation of the 16,200 ft long cutoff wall in Task Order No. 3. One of the significant achievements of this project includes the use of a hydromill cutter in the self-hardening slurry method of cutoff wall construction. 16 pp. 2 references.