In August 2005, Hurricane Katrina produced storm surge which breached the New Orleans Levee System and caused billions of dollars in damage to the greater New Orleans area. In the aftermath of the hurricane and the resulting destruction, federal legislation provided for funding needed to rebuild the New Orleans Levee System.
To meet the ultimate goal of protecting property in and around New Orleans, the US Army Corps of Engineers (USACE) designed a levee system which would provide 100-year level storm surge protection. A plethora of design and construction techniques were used in the levee improvement projects, some of which included geosynthetic reinforcement, and WBV-72 was one of several levees to incorporate a high strength polyester woven reinforcement geotextile in its design and construction.
WBV-72 is part of the Westbank and Vicinity (WBV) Hurricane Storm Damage and Risk Reduction System (HSDRRS). It is located in St. Charles Parish, La. and serves the HSDRRS as the Lake Cataouatche Western Tie-In Levee. To the west, WBV-72 connects to WBV-73; to the east, WBV-72 connects with WBV-17b.2, running parallel to US Highway 90. WBV-72 is a clay levee, measuring 2.8 miles long. This project included construction improvements to a 2.4-mile section of the levee raising the elevation by 13.5 feet and offsetting the alignment behind the existing levee, thereby moving it farther back.
The area on which the levee was to be constructed consisted of soils with varying degrees of weakness. Because the USACE was operating on such a tight deadline, a soil-consolidation approach which would have taken multiple years, was not possible. After considering various options, the USACE decided geosynthetic reinforcement was the most economical and least time-consuming technique to increase the unacceptable shear strength of the levee foundation soil.
In March 2010, construction of WBV-72 was awarded to WRS Compass Contracting out of Tampa, Fla. WRS accepted the award knowing that construction of the WBV-72 levee must be completed by June 2011. Since geosynthetic reinforcement was needed below the levee and during early phases of construction, finding a reinforcement supplier was a high priority.
During the bidding portion of the project, HUESKER proposed using custom length factory sewn panels, manufactured to closely meet planned geotextile limits, thereby reducing waste and construction time. To keep material cost down, HUESKER also proposed a custom-produced geotextile that closely met the specified 5% wide-width tensile strength properties of the project. After careful consideration, WRS Compass awarded the geotextile contract to HUESKER, due to the short lead time availability.
WRS Compass and HUESKER worked together to finalize the layout plan for the geotextile panels. In the end, six roll lengths were produced to optimize material efficiency. Due to varying levels of shear strength experienced in the levee foundation soil, the USACE designed five geotextiles based on strength at 5% strain per ASTM D-4595. HUESKER proposed three custom produced geotextiles that met all project 5% strength/strain specifications, more closely matching USACE’s five strengths than available off-the-shelf geosynthetic options. Because HUESKER was able to produce high strength at low strain polyester geotextiles, tensile strengths at 5% (see table below) were achieved while maintaining the economic goals of the project.
|Property||Test Method||Stab 490||Stab 650||Stab 830|
|Tensile Strength @ 5%||ASTM D4595||15,000 lb/ft||20,000 lb/ft||27,420 lb/ft|
The embankment foundation soils at the WBV-72 site were weak. The Stabilenka geotextiles installed at the subgrade served to reinforce the base of the levee while additionally separating the poor foundation soils from the overlying embankment. By reinforcing the weak subgrade below the base of the levee, the poor onsite foundation soils did not need to be removed and replaced with a structural fill, which would have been significantly more expensive. In addition to cost savings, reinforcing over the subgrade with HUESKER’s Stabilenka eliminated risks of differential settlement and slip plane failure. HUESKER’s Stabilenka products provided an economical and viable design and construction option for the WBV-72 levee improvements. The use of Stabilenka geotextiles resulted in significant cost and time savings.
As in the case of WBV-72, where embankments are built on soft or weak subgrades an overly rapid construction program may lead to bearing or slope failure if the shear strength of the subsoil is exceeded. The incorporation of Stabilenka between subgrade and embankment fill serves to increase bearing capacity. Structural stability is thus guaranteed, even during the consolidation period. Stabilenka allows embankments to be built on practically all soft soils.
Reliable reinforcement fabrics are always characterized by their favorable stress-strain behavior; they should exhibit a combination of high tensile stiffness and low-creep properties. Through HUESKER, you can reap the benefits of German engineering in American made products. HUESKER offers high-performance products based on decades-long manufacturing experience and in-depth expertise in high modulus fiber technology.
Unlike many alternative products on the market, Stabilenka is manufactured from special multifilament yarn that allows the achievement of moduli exceeding 3,000,000 lb/ft. Users thus benefit from a premium product which is unmatched worldwide. Stabilenka is capable of mobilizing high-tensile forces at low strains to offer maximum reliability, exhibiting an extremely low creep strain of less than 1% when subjected to a permanent load equal to 50% of the short-term strength after the construction phase.