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North American Trevi Group subsidiary Treviicos has rehabilitated more than 42km of the Herbert Hoover Dike after 14 years of work on the US Army Corps of Engineers’ (USACE's) rehabilitation programme.
Treviicos was awarded its first task order on the project in 2008 by the USACE, which had classified the historic dam in south central Florida as an unsafe water control system a year earlier.
The 230km long earthen Herbert Hoover Dike surrounds the second largest freshwater lake in the United States. Built in multiple phases starting in 1910, the dam had been showing performance issues during high water events. These included movement of dike material, such as sloughing, the development of ground collapses and other erosion.
The rehabilitation programme has sought to improve the dike’s stability by minimising the water seepage thorough the levee foundation and limestone layers below.
One of the main components of the rehabilitation has been the construction of a cut off wall that acts as an impermeable barrier along the levee’s crest alignment.
Operating as specialty general contractor, Treviicos has so far installed approximately 600,000m2 of cut off wall to a maximum depth exceeding 25.9m and as such has rehabilitated more than 42km of the dike.
To install the cut off wall Treviicos employed two types of technologies: jet grouting and self-hardening slurry.
It used the jet grouting method to close the areas adjacent to existing concrete structures. Treviicos also applied a combination of pre-drilling and jet grouting techniques.
Pre-drilling was employed to fragment the hard limestone layers along the alignment of the cut off wall. Meanwhile the jet grouting was performed to create the required cut off using a Soilmec SR30 rig set-up mainly with a mono-fluid jet grouting system.
It used the self-hardening slurry technology to ensure stability of the dike during the excavation for the cut off wall. This technology employed the hydromill method, in which the slurry, an engineered mix of Portland cement, slag cement, bentonite, additives and water, act both as support of excavation and permanent backfill.
Treviicos then performed the excavation using a combination of mechanical clamshell and a hydromill. The former excavated the softer soil layers. The latter excavated the more competent ones and limestone layers from its mount on a Soilmec SC120 heavy duty crane.
All phases of the rehabilitation programme included additional scopes. Treviicos also worked on a programme of verifying the compliance with strict technical requirements, continuous environmental monitoring, slope protection during production, full site restoration upon completion of site activities, electronic data management, and installation of an automatic data acquisition system for the future real-time monitoring of groundwater levels underneath the dike.
Treviivos has completed seven task orders ahead of schedule and expects to complete work for the programme by the end of this year. It landed its last task order on the dam in 2020.
Bauer’s US business Bauer Foundation Corp has also been involved in the dam rehabilitation programme. It secured a further contract to stabilise the dam in 2019 following successful completion of earlier work on the structure.
The rehabilitation works are part of USACE's US$870M (£753M) investment in projects and safety measures at Lake Okeechobee to reduce the risk of catastrophic failure and flooding for a large area of South Florida.
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