The Works Progress Administration under the terms of the New Deal built thousands of feet of stormwater box culverts in the late 1930s throughout Kennett, Missouri.

Fast-forward nearly a century and the deteriorating culverts were a problem city officials needed to address, particularly a portion running under residential properties posing a sinkhole risk to homes. But what was the best method for tackling that problem? The culverts were rectangular and, being hand-built, were roughly 18 by 30 inches though those specs weren’t exact.

Thermoform liner from Warrior Trenchless Solutions ended up being the ideal solution. The PVC alloy liner has the ability to expand into whatever the shape of the host pipe is, making it well suited for non-round or irregularly shaped structures like Kennett’s 1930s era box culverts. Over three weeks in late February and early March, Pipeline and Drainage Consultants out of Fort Mitchell, Kentucky, successfully used the Thermoform product to line almost 1,200 feet of Kennett’s aging box culverts. 

“With lining in general, until you get the camera in there and look at everything to make sure it’s OK, it’s always a little nerve-wracking,” says Doug Brossart, co-owner of Pipeline and Drainage Consultants. “You just hope everything works out and everything did work out pretty well actually.”

Stormwater solutions

Pipeline and Drainage Consultants was started in 2015 by Brossart and his brother Don. They’re also affiliated with Spartan Construction, a Kentucky utility and highway construction company in operation since 1982 and owned by their mother. Pipeline and Drainage Consultants focuses on stormwater inspection and rehab and does work throughout the Southeast U.S.

The company discovered Thermoform while looking for a product to compete in the cured-in-place pipe market.

“We had been doing a lot of sliplining and spin casting, but we really didn’t have a product to compete with CIPP lining,” Brossart says. “We went to WWETT a few years in a row trying to figure out what product we were going to get into and ended up teaming up with Warrior.”

The WWETT Show is also where Kennett officials talked to Warrior and learned about Thermoform liner, ultimately getting paired up with Pipeline and Drainage Consultants for installation.

Cleaning challenges

Pipeline and Drainage Consultants started the beginning of the work last year, initially visiting Kennett to do some preliminary condition assessment and cleaning of the box culverts.

“We went out there in October to do some light cleaning and get our cameras in there to see how bad it was,” Brossart says. “They were hand-built and just formed by what looked like 1x4’s and 1x6’s. I guess a lot were built before the city was even really established in the area, so some were running under houses and they were in really bad shape. There were 3- or 4-foot sections missing where it was just rebar. We had to be really careful cleaning it to not make it any worse. After we got one clean and ran a camera back in there, we’d see all this debris. We realized we were causing the debris. We were eating the sides of the structure out.”

Ahead of the scheduled February/March rehab work this year, Pipeline and Drainage Consultants was on the hunt for a better method for doing the pre-lining jetting of the culverts. In addition to the poor condition being a cleaning challenge, some of the culverts were not straight shots.

“That gave us another challenge because all the jetting equipment wants to rub one side when the culvert is on a curve,” Brossart says. “The angles of the heads were eating the sides of the box out because the concrete was so rotten. We were getting them clean but also making the boxes worse. We were worried we were going to undermine the stability around these culverts.”

Pipeline and Drainage Consultants took the problem to KEG Technologies, which provided a twin jetter setup using OMG nozzle heads.

“All of their velocity is straight back from the head, instead of right or left of it or up and down,” Brossart says. “With most of the pressure from those heads going straight back, we weren’t eating up the sides of the box, which was one of the main problems we were having when we initially started jetting. Those OMG heads, all of their velocity is straight back and it really made a big difference in the way we were cleaning.”

KEG Technologies representative Danny Manning even came out to the job site for a few days to assist the jetting crew.

“After some trial and error we got the culverts pretty clean the best we could,” Brossart says. “It was kind of get them clean with as much power as possible without tearing up what’s already there. So there was a fine line.” 

Pipeline and Drainage Consultants ran the twin jetters from its Vactor 2100, often at 80 gpm and 2,000 psi.

“We would sometimes take one of the heads off and run them single. We did a lot of experimenting with the amount of jets, playing around with it until we got the right recipe on everything,” Brossart says. “We would pull in and then follow with our camera. See if we were cleaning it or tearing it up. We had to keep an eye on it.”

Slow and steady

Brossart says his company had never lined anything square-shaped before, so he relied on Warrior for the Thermoform liner specs.

“We worked with their plant to come up with the right size liner and wall thickness and create something that would blow up in the culverts properly,” Brossart says. “In talking to Kennett, they said nobody had seriously considered lining. They’ve done some CIPP on several occasions but this was their first attempt at lining those square culverts.”

The work focused on 1,140 feet of the approximate 10,000 feet total that runs throughout the city.

“They’re hoping to maybe do some more as they get money in their budget,” Brossart says. “These first ones were all the ones underneath houses where there was concern about a sinkhole showing up under someone’s home.”

Once the lining crew got started, it took about a week to finish the job. Six runs in total were done.

“We were basically doing a run a day,” Brossart says. “We would set everything up. The liner takes a couple hours to get heated up. We’d pull it in, cool it down and then go in to cut the ends off. It took the better part of a day to get that done.

“We added some extra heat and extra processing time because the culverts were square and we wanted to make sure the liner was going to fill those corners up. That takes a little longer. We were just being extra careful, making sure the liner would expand in those corners best it could. We did everything slowly and carefully because it was a learning curve for all of us.”

Conform to any pipe shape

Thermoform is a PVC alloy or a copolymer product, which is what made it a good fit for lining the shape of Kennett’s box culverts.

“What sets it apart from the more traditional CIPP liners you see is that all those liners are, in simple terms, manufactured on site in the host pipe through the curing process whether that’s initiated through steam, hot water or a UV light,” says Robin Hershman, business development manager at Warrior Trenchless Solutions. “You’re initiating a chemical reaction inside your host pipe to cure that liner. The finished quality of that liner really depends upon the conditions on site and the quality of that chemical reaction. With our Thermoform product, all those factors that control the finished quality of the product are determined at the point of extrusion in the plant. Things that engineers look for like tensile strength and wall thickness — all of that is determined at the point of extrusion and it does not change throughout the course of the installation process. It has the unique ability to, even though it’s extruded round, expand into and conform into whatever shape the host pipe is once we get it warm and hit it with steam. That’s why we’re able to line things like the box culverts.”

Hershman also notes that Thermoform has benefits from an environmental standpoint. Given some of the recent media coverage and ongoing research concerning the lining process and potential VOC and styrene emissions, Thermoform is an attractive alternative to people with those concerns.

“The only byproduct of our installation process is pure water from the condensed stream,” Hershman says. “No styrenes or VOCs of any sort are released during the installation of the product. It’s really because we’re not initiating a chemical reaction. All we’re doing is heating and changing the shape of an already extruded pipe.”

Successful outcome

The week of lining work in Kennett went fairly smoothly in the end, Brossart says.

“We had talked about it so much in advance that the lining went about how we expected it to go,” he says. “We had a lot of discussions with the Warrior plant people on what size the liner was going to be and then Warrior had their field installing guys there to help if there was something a little unforeseen. The biggest issue for us was more on the cleaning side. Just getting the culverts clean enough without tearing them up worse was our biggest challenge. But the lining, we maybe even overthought it. We were so concerned about whether it was going to work or not.

“Once you pull the trigger on having the liner made, you have to put it in. It was a little nerve-wracking the first one, but once the first one blew up in there OK, it felt like the rest of it was going to go OK. Kennett was happy. I think they’re going to do a little more every year until all the box culverts are lined. We’d bid on the work again. It was a little bit of a learning curve, but I think we now have a good familiarity with making it work there.”