In fall 2010, Indiana DOT crews lined 14 corrugated metal culverts — 2,257 linear feet total — with HDPE. At $1.2 million, they saved taxpayers about 50% on labor compared to contracting the work. Oval pipes ranged from 30x46-inch to 72x102-inch; round pipes from 48 to 84 inches in diameter. Photo: Indiana DOT
Once the HDPE liner's installed, it's important to build a bulkhead or plug to secure material in the annular space during grouting. Grouting was contacted separately; Temple & Temple Excavating and Paving's Patrick Howser puts the finishing touches on a culvert on I-65 in Indiana. Photo: Indiana DOT
Gaining installation expertise
Launched in 1962 to install underground golf course irrigation systems, ISCO Industries bought the Snap-Tite patent shortly before the turn of the century. In 2008, the American Association of State Highway and Transportation Officials approved the product (Standard M326) for rehabilitating culverts beneath roadways.
District managers followed typical procedure for competitive bidding, calculating material costs through a quantity purchase agreement and factoring in equipment rental, employee labor and benefits, and items like maintenance of traffic and purchasing materials through a standard maintenance contract. The request for proposal including specifications for liners, and IS-CO Industries responded with the lowest acceptable bid.
Thanks to the liner's smooth profile, the inside dimension can be smaller than the original pipe yet provide the same flow characteristics. This attribute came in extremely handy when, in one case, the pipe was deflected approximately 9 inches, potentially requiring a smaller size. After conducting a hydraulic study, district engineers concluded flows would remain adequate.
Typically, the district's maintenance crews consist of four to five employees. For the pilot program, three were experienced employees and one or two were college-aged summer interns. The distributor and manufacturer taught all of them how to handle and install the system's components: liner sections, skids to slide the liners on, and grout tubes. Required equipment included a backhoe, come-a-longs, steel cabin slings, ratchet chains, water pumps, foam generators, and concrete pumps. No fusion equipment was needed.
Employees were trained to prepare the existing pipe for sliplining, which includes:Installing any necessary blocking to ensure the liner wouldn't float during the grouting processInstalling any necessary runners on the bottom of the pipe if the liner is in danger of snaggingPlacing grout tubes to make sure all annual space gets filledProperly positioning the linerPreparing the liner sections to snap togetherPlacing the gasketApplying spray lubricantAfter installation, constructing a bulkhead or plug to secure material in the annular space during grouting.
To prepare for installation, district employees entered a pipe to look for debris, collapsed sections, and areas that had the potential to cave in. Once the asset was cleaned, measured, and inspected, liner was trucked from Bedford, Ind., to the project location and assembled onsite.
A 24-foot, 54-inch outside diameter round liner weighs 2,873 pounds. During installation, wood blocking and runners support the liner to keep it from floating up during grouting and ensure it matched the existing culvert flow line as closely as possible. Crews positioned liner sections using chains, binders, and come-a-longs. They installed a gasket on the male end of each section before inserting that end into the female end of the adjoining liner and snapping the two sections together. They then used a backhoe to push the assembled sections into the existing pipe.
Though the agency has installed liners up to 315 feet long, most of the culverts in this project were under interstates and had linear runs of 200 to 250 feet. Total liner length is dictated by the size of installation machinery; some Indiana contractors have pushed more than 600 linear feet. The greatest limiting factors are the liner's total weight and resistance to pushing.
Once the entire liner was installed, Temple & Temple Excavating and Paving Inc. of Salem, Ind., was contracted separately to grout the space between liner and pipe using a concrete pump. To ensure annular spaces and voids filled properly, the grout was delivered via a 2-inch hose with fill tubes installed in the pipe at 100-foot increments.
“Grouting's one of the most critical parts of the process; the pipe can collapse if it's not done correctly,” says Temple & Temple's Patrick Howser. “To make it lighter and flow more easily, we introduced air bubbles into cellular grout onsite with a Vermillion LLC and Associates foam generator.”Refining liner ordering
Crews soon were able to install a liner in two to three days. They shared their knowledge with coworkers in the La-Porte District, then with employees at the agency's five other districts. Since 2010, the agency has sliplined approximately 46 assets statewide, with each district performing at least one installation.
The LaPorte crews uncovered and resolved a couple of unexpected difficulties their successors learned from:Some culverts needed to be cleaned of debris or standing water, and a few required jetting out. On several occasions, dewatered pipes were refilled by rain, which slowed installation. Pumps were used to pump standing water out of flooded culverts.Settling and sinking beneath large expanses of roadbed altered the interior diameter of some sections up to 24 inches, compared to those outside the roadbed, so liners that should have fit didn't. The state began requiring crews to crawl through the pipes, measuring the interior diameter every 20 feet to ensure properly sized liners would be ordered.
In addition to HDPE, the agency allows PVC and cured-in-place liners and is evaluating spiral-wound and centrifugally cast liners. Opening the door to more rehabilitation using HDPE liners has reduced the cost of similar projects. Contractors are more actively vying for such work, so overall bid amounts have declined. This in turn has enabled the agency to redirect crews and funding toward other preservation activities.
“Overall, we saved an average of 20% to 50% by doing this work in-house,” says Pinkerton. “Contractor cost has come down to what it would with our own forces. We also may have shown that more contractors could get into this type of work and be profitable.”
*Not to be confused with autoclave experts Snaptite Inc. and Snaptite Hose Inc. of Erie, Pa.
— Hauersperger (firstname.lastname@example.org) is Assessment and Scoping Engineer for the Indiana DOT's LaPorte District.