Trenchless Structural Spray Helps PennDOT
Turn Nightmare Into Dream

By: Suzan Marie Chin and Mary Shafer
    

 Harrisburg nestles between the eastern slopes of Pennsylvania’s tightly packed Allegheny Mountains and Cumberland Narrows of the Susquehanna River. The city of nearly 50,000 people is surrounded by small towns that have been absorbed into the sprawling state capitol.

The Harvey Taylor Bridge connects Route 11/15 — called North Front Street in Wormleysburg — with the capitol’s busy downtown and government complex just on the other side of the Susquehanna. Beneath this bridge on the Wormleysburg side is a culvert that collects water from a small tributary, along with storm runoff from the bridge. The culvert sends this water directly into the river through a double-barrel set of 75-foot-long, 54-inch diameter corrugated metal pipes.
 

About a half-mile to the southeast sits the John Wormley House Historic Site, home of the city’s founder. Next to this site, another double-barrel set of similar stormwater pipes—these 88 feet long and 60 inches in diameter —drains out to the river.

This stretch of North Front Street, which runs along a preserved riverfront park area, has an Average Daily Traffic (ADT) factor of roughly 17,000 vehicles. So when a Pennsylvania Department of Transportation’s (PennDOT) inspection revealed the beginnings of serious structural deterioration and crushing (known as deflection) in both sets of pipes, it was a nightmare scenario.


Not Digging the Situation

“When we started this project in 2000, we tried to do it locally, in-house,” recalls Nexa Giboyeaux, PennDOT Highway Design Project Manager. “Due to traffic control issues, we never finished that project. We could never replace those pipes.” In 2007, she took control of the project, hiring engineering firm Larson Design Group (Montoursville, Penn.) as consultant, to conduct a problem study and solution analysis.

Larson determined the problem was the pipes depth. At 20 feet below ground, replacing them would mean significant surface disruption through excavation. It would mean digging a 10-foot-by-20-foot trench on each site to allow for required upsizing of the pipes to box culverts. This would have been necessary to bring the circa 1945 pipes up to modern code standards for water conveyance structures. Then the trenches would have to be backfilled and road approaches milled and re-paved.  And all of this would have to be done without compromising the environment or the historic site.

Even with detours, most of the work would have to be done at night to reduce traffic impact.  This would require roughly 10 weeks of site preparation, followed by dig-and-replace work, per pipe — a total of roughly nine months and $4.2 million to complete the project…and that was if the culvert beneath the bridge didn’t require upsizing.  

Giboyeaux knew this was not feasible. She tasked Larson with researching alternatives while she also spent time seeking information on the Internet.

SprayRoq Spraywall’s polyurethane coating was pushed to the forefront of available options, as much for its structural strengthening and protective characteristics as for environmental concerns.
Larson gave a presentation of Larson’s and Giboyeaux’ findings to a gathering of PennDOT supervisors arranged by Giboyeaux. She says, “That’s where we put it down to cost, time, the impact that we have to have, and we decided to give it a chance and try out (SprayWall).”

Abel Recon, infrastructure rehabilitation contractors based in Mountville, Penn., won the bid to apply the SprayWall.  

Surprisingly Fast Process

Logistically, the two sites were not challenging. “We did the whole project with a spray truck, a prep truck, and a pickup truck,” says Abel’s general manager Hap Witmer. “We just parked in the normal parking spot alongside the road and worked out of those.” Abel worked the sites with a crew of seven, taking hoses into the pipes from the tops of the culverts.

First, temporary walls and dikes were created using boards and sandbags to divert the water flow from the work pipe into its twin until rehabilitation was complete.

The existing structure was coated with a coal-tar epoxy.  Most of the epoxy was intact and offered good adhesion with the SprayWall coating, but Abel pressure washed any loose material from inside the pipe. The technicians installed tightly woven “silt sacks” at the end of the pipes, allowing water to flow through but catching any debris.

Next, grouting was needed to restore the corrugated profile of the pipes near the pitted exposed ends. “There were some pinholes and maybe some one-inch holes,” Witmer explains.  “But other than that, the rest of it was in fairly good shape.”

This surface preparation work was completed during a single 12-hour day shift for each pipe.  Then, the night crew came on and spray-applied the polyurethane.
The structural coating was applied at 500 mils thick, based on the ASTM 1216 material design equation for structural integrity. American Testing of Lancaster was hired as a third-party inspection consultant to ensure objective results.

Application was achieved at a rate of about 10 feet per hour.  Roughly 15,000 lbs. of material was used for all four pipes.  Given the quick cure time, water flow could be restored within minutes of finishing the coating application and thickness testing.

Enviable Results

While the original budget scope was $4.2 million, the pipe rehabilitation cost alone was $275,500, and the entire cost of the project was $1.4 million — a savings of $2.6 million. As opposed to 10 weeks per pipe replacement, the project took only about four days per dual pipe rehabilitation. “The savings were that big because we didn’t have to have traffic impact and we didn’t have to do all the restoration that we would have had to if we’d replaced the pipe,” asserts Giboyeaux. 

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