S-155

Recently the Madrid Engineering Group/Spencer, White & Prentis Foundation Corporation team was selected to complete a design build emergency response to repair water control structure S-155. The solicitation for proposal was presented and subsequent contract administered by the Southwest Florida Water Management District.

The design construct team complimented each other by utilizing their individual skills. Spencer, White & Prentis brought to the table 80 plus years of specialty geotechnical construction and design experience, while MEG brought general construction and design experience. The overall project approach was expedited due to technical understanding of the project and spirit of cooperation.

The water control structure straddles the Hillsborough River and is the last flood control structure on the river before the water reaches Tampa. S-155 was constructed by contractors working for the U.S. Army Corps of Engineers in the late 1970's. The structure consists of a 30-foot tall earthen embankment, an adjustable broad crested weir, concrete abutments and bridge deck and A36 sheet pile wing walls. The sheet pile wing walls were originally driven with a vibratory hammer and restrained with an internal waler and tie back system. The tie back system extended 80 feet into the earthen embankment where it was secured to a dead man anchor.

The downstream wing walls had begun to deflect substantially over the past few years. The restraining bolts charged with the responsibility of holding the sheet pile to the waler were failing with fully half of them being on the river bottom. The situation had become dire and immediate design and remediation was required.

Madrid Engineering Group along with Spencer, White, & Prentis was charged with the responsibility of designing an engineered system that would prohibit further movement of the affected wing walls. Our solution to this complex problem was very straightforward and included the use of soil anchors and an external waler system to restrain the wing wall from moving further.

Our team completed six soil borings, laboratory testing, anchor design, structural analysis, barge mounted horizontal drilling, anchor installation, anchor grouting, load testing, and site work. Anchor depths ranged from approximately 70 feet to 90 feet in length.

Drilling was completed by utilizing a D-4 adapted to drill horizontally through the holes cut into the sheet pile retaining walls. All the drilling work was done from the waterward side utilizing modular barges as a staging and work platform. The drill was equipped with a grout pump making the entire operation self-contained.

Upon completion of the anchor system, the external walers were mounted to bearing saddles and welded into place. Prior to final tensioning of the anchors, each anchor was tested to 1.5 to 2 times the design load, thus assuring the integrity of each individual anchor.

To further increase the factor of safety for this project we utilized a lightweight fill product provided by Atlanta Construction Fabrics (ACF). Specifically, we utilized a product named Geo-Foam. Geo-Foam is a light weight foam product that weighs 1 pound per cubic foot and has been utilized as embankment fill over soils that have low shear strength. In this application, we utilized the product to reduce the vertical and related horizontal stress behind the wall. The Geo-Foam was ordered in 3 foot by 4 foot by 12-foot sizes. Installation required an underdrain and a geotextile fabric as a separator. After fill placement, we covered the material with 2 feet of fill and an additional foot of rubble riprap.

The project has been completed successfully with the walls not only being stabilized but even nominally restored vertically.

Placement of Geo Foam blocks adjacent to the wing wall at Structure S-155

Aerial of S-155