Go Big or Go Home

The City of Fort Worth, Texas, is all about water.

In 1914, the people of Fort Worth wanted a lake, so naturally they just built one. As you would expect big things from Texas, when Lake Worth opened, it was the largest municipal park in the world, as declared by the Fort Worth parks commissioner. One hundred years later, Fort Worth continues to thrive and keeping the water flowing is a key to its future growth.

As with all cities of its age, the infrastructure serving Fort Worth is showing signs of aging. The storm drain system in the downtown area has begun to deteriorate and in some locations has developed voids that are starting to affect its structural integrity. The City of Fort Worth is committed to maintaining and protecting the aging infrastructure, but must be mindful when renewing service of disturbing historic areas around the city that are important culturally, socially and economically. So when it came time for the city to rehabilitate the storm drain serving the historic parts of downtown Fort Worth, city officials faced many challenges and set high expectations for the firm that would win the project.

The project called for rehabilitation of 1,000 lf of deteriorated storm drain. The existing host pipe was a 48-in. x 42-in. stone arch pipe and is the original, which had served the city well for years, but over time, the grout had worn away allowing for the development of major voids and infiltration. Therefore, any solution decided upon needed to provide significant structural support. To further complicate the job, the sewer had four small diameter (24-in.) manholes, which limited access and options for repair.

The specifications of the project alone were enough to make any contractor think twice about attempting to take on the Fort Worth job. Not least of all, the 48-in. x 42-in. arch-shaped host pipe posed a challenge to most modern rehabilitation solutions. Ancillary project constraints, such as a small work window that further restricted hours to 9 a.m. to 4 p.m., created additional challenges for any contractor considering this job. Other constraints included a requirement that the construction zone had to be “reset” every night to its original condition before the start of morning traffic. Plus, any manhole work in certain busy intersections could only be performed at night due to traffic volume concerns. If that wasn’t enough, the work location was in a high visibility part of town, surrounded by three large banks and city government buildings, so any interference with traffic would not go unnoticed.

Solution

A consulting firm, Brown & Gay Engineering out of its Fort Worth office, was brought in to evaluate the situation.  The firm eliminated the option of simply replacing the grout because it would only act as a band-aid solution and not a long-term fix. After careful consideration and due diligence, Brown & Gay recommended the following options for rehabilitation: traditional cured-in-place-pipe (CIPP), geo-polymer spray-on concrete and Spiral-Wound PVC rehabilitation.  

CIPP was the traditional choice because of its quick installation and structural strength. However, the odd shape of pipe made CIPP expensive because of the thickness of the bag required to meet the fully-deteriorated load rating and the challenge of inverting the liner into the host pipe shape. In addition, the narrow manholes would require temporary removal and replacement for CIPP installation that would impede traffic flow and, therefore, not meet one of the major goals of the city. A geo-polymer spray-on concrete solution could also work to fill in the voids and grout, but due to the need for meeting the fully-deteriorated load rating, it would require an extremely thick application, which poses application issues and costs, as well as reducing the hydraulic capacity of the resulting pipe.

Enter SAK Construction to solve the rehabilitation challenge with a solution that met all the City of Fort Worth project goals and requirements. Using a new technology called Spiral Wound Rehabilitation (SPR), the company repaired the sewer line with little to no disruption while meeting all the accompanying restrictions imposed by the historic location of the job. Since SPR equipment is quick and easy to set up and disconnect, SAK could pull the equipment away, take down all traffic controls and replace the manhole cover to leave the work zone as if it had never been touched in preparation for the next morning’s commute. No trench, bypass or cure-time is needed so SAK could disappear every afternoon without a trace.

Planning, while important in any job, was a key factor for this project in avoiding traffic issues. The SAK team spent many hours coordinating the timing of the rehabilitation with the city traffic engineer and together they created a game plan that worked both for the traveling public and the contractor. The result was the decision to complete removal of all equipment every day, which was possible because of the flexibility of the SPR solution.

The project proceeded with SAK installing a circular-shaped SPR solution with steel reinforcement within the profile. Adding a cementitious cellular grout that filled both the annular space and any voids behind the stone host pipe resulted in a solid structural enhancement while shoring up the voids behind the host and maintaining the hydraulic requirements within the host pipe. In essence, what SAK provided Fort Worth was a concrete pipe with a PVC invert.  Reinstating the services was also a challenge because there were a large number of laterals (24 in. total that ranged from 8 to 24 in. in diameter). Further, due to their size and distance, the laterals had to be reinstated while manually traversing the rehabilitated host pipe to reach them.

Project Success

Overall, the 90-day installation goal was met and the project came in within a budget that was 20 percent lower compared to the other technologies bid. Because of the strong focus on upfront planning, SAK never caused any traffic disruption, which was especially appreciated by the fire station located around the corner.
The project was completed with zero complaints to Fort Worth, which was a comforting result for the city. Adilda Cazorla, construction inspector for the City of Fort Worth, stated, “We went through this difficult project with zero complaints. The location of the project, plus the working hour allowance made it even harder, and it was done in less time than was expected. This job, besides being trenchless, was also painless.”

Michael Owen, P.E., project manager for the city, stated, “SPR was clearly the right choice for this project, as it allowed for minimal surface disruption and provided a 50-year solution meeting the hydraulic requirements. SAK performance was excellent, as they were able to meet all of the city’s requirements and deliver the project on time and on budget. We look forward to opportunities to work with them and this project on future rehabilitation needs.”

Jim Kalishman is chief information officer at SAK Construction, based in O’Fallon, Mo.