Microtunneling the Harbour Island Force Main

Vadnais Completes Long Crossing for Force Main Installation in Florida

The Harbour Island Force Main is an essential pipeline in the City of Tampa’s wastewater system. Placed into service in 1951, it conveys more than 15 million gallons, or 30 percent of the City’s wastewater from the Hillsborough River corridor to the Howard F. Curren Advanced Wastewater Treatment Plant on Hookers Point.

Since 1976 the City of Tampa has replaced and relocated several segments of the force main and has upgraded the Krause Street Pumping Station. Due to the deteriorating condition of the approximately 9,000 lf of the original pipe and the critical service the force main provides to the City’s wastewater system, the City embarked on the Harbour Island Force Main Replacement Design-Build Project.

Microtunneling the Harbour Island Force Main

This project includes all engineering and construction services necessary to modernize the remaining original components of the force main. It included the evaluation of pipe and pipeline route alternatives, preliminary surveys and soil sampling, selection of alternatives, final design and construction. The design-build process assisted the City in delivering a cost-effective, reliable wastewater pipeline that will serve future generations.

Kimmins Contracting Corp., a well-respected local civil contractor, who is celebrating their 100th year in business in 2023, was selected by the City as the design-builder. Kimmins teamed with Wade Trim to provide the Engineering and Design Services. The key component of the project is the installation of approximately 9,000 lf of 48-in. and 54-in. force main pipeline from the Krause Pump Station to the Curren AWTP.

Crucial to the success of the project was a long, subaqueous crossing of the Ybor Turning Basin from the Gulf Marine shipyard to the Cotanchobee Park adjacent to Amalie Arena. A 3,156-lf, 78-in. diameter steel cased microtunnel was designed to be installed beneath the Ybor Turning Basin to reduce the length of the pipeline route and impacts to the local businesses and residents. A 54-in. carrier FRP force main will be installed in the casing, making connections on both the west and east end of the Ybor Turning Basin.
To design and construct microtunnel crossing, Kimmins partnered with Vadnais Trenchless Services Inc. (VTS), a Primoris Services Corporation company. VTS is a specialty general engineering contractor that has been in business for more than 60 years. VTS entered the microtunneling business in 1993 and have been successfully performing microtunnel installations ever since. Through the end of 2022, VTS had installed more than 265,000 lf of microtunneling throughout much of the United States.

VTS’ scope of work consisted of designing, furnishing and installing a single reach of 3,156 lf of 78-in. OD steel casing by microtunneling method with the installation of 54-in. pressure fiberglass reinforced polymer mortar (FRPM) carrier pipe for the new sewer force main. VTS was also tasked with the design and installation of two secant pile shafts approximately 80 ft deep on either side of the Ybor Turning Basin. The jacking shaft was 40 ft inside diameter and the reception shaft was 20 ft inside diameter. VTS subcontracted the shaft construction to Ebsary Foundation Co. of Miami, Florida. The microtunnel crossing was installed primarily in limestone, clay and dense sands beneath the Turning Basin. The entire tunnel alignment was approximately 60 ft below the water surface in Tampa Bay.

The launch and reception shafts were completed in late August 2022.

The MTBM (an MTS 1970) was launched in early September 2022. The MTBM was designed as a five-piece machine, (cutterhead with face access and articulating steering joint, a second steering joint to assist in steering if soft ground was encountered, a decompression chamber section for three men, decompression operation section and the MTBM powerpack section) with an overall length of 53 ft. The jacking system deployed on this project was an MTS 1250-ton indexing frame in the launch shaft assisted by six intermediate jacking stations (IJS), each with a capacity of 1,000 tons. The lubrication for the tunnel was accomplished with an MAT SCC-12-C colloidal mixing plant and 78 automated lubrication stations.

VTS deployed one of its large Derrick separation plants and a 7200 big bowl centrifuge working in tandem with a large Kubco centrifuge. The entire crossing was achieved using a strictly water-based slurry without bentonite. Trinity Products LLC (Tri-Loc) supplied the 78-in. OD x 1-in. thick weldless interlocking steel casing on the project. To mitigate risk during the crossing, VTS and Tri-Loc agreed to seal weld all the joints.

As the tunneling was beginning to hit its stride, Mother Nature intervened with Hurricane Ian headed directly for Tampa on Sept. 28, 2022. VTS crews did extraordinary work to prepare in 48 hours, dismantling most of the topside equipment and welding off the tunnel with a steel bulkhead anticipating the shaft would be flooded. Fortunately, the storm turned east about 100 miles south of Tampa. The devastation to the area where the storm made landfall was enormous. VTS was fortunate to escape relatively unscathed and was back in operation in about a week.

Tunneling production was variable across the drive as the MTBM encountered different materials from clay, limestone and gneiss near the end of the drive. The cutting tools were not changed during the 3,156-lf drive. The lubrication program was well planned and executed, resulting extremely low jacking loads of around 550 to 700 tons during jacking operations. Most impressively, the IJS’s were not activated until the machine recovery process.

The carrier pipe in the tunnel is 54-in. Hobas pressure pipe. Once installed annular grouting will occur and the tunnel will be complete. This microtunnel is the third-longest completed in North America and the longest steel cased microtunnel in the Western Hemisphere. Great planning, 30 years of experience and great teamwork between Vadnais and Kimmins made this achievement possible.

Dan Schitea is vice president of Vadnais Trenchless Services, Inc.

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