When the city of Fort Worth experienced a soil degradation problem caused by a bad bottom in a 78-inch corrugated metal storm drain in the spring of 2008, it became bad enough to cause a sinkhole that allowed water to shoot through during a heavy rain and destroy both a residential yard and a driveway. The city of Ft. Worth replaced about 100 feet of the worst affected location of the 1,000-foot-long storm drain with reinforced concrete pipe. Because soil degradation and corrosion occurred along the length of the entire pipeline, the city contracted engineers to design a long-term repair for the entire length of the storm drain. Unfortunately, when the city put the project up for bids, there were no bidders, because the plans called for casting a new concrete bottom along the entire 1,000 feet of the pipeline.
The city then asked Uretek ICR Gulf Coast to recommend a solution. Uretek ICR specializes in concrete lifting, infrastructure repair, and soil stabilization. Uretek ICR determined that it was possible to repair, stabilize and seal the corrugated metal storm drain line utilizing their patented HDP (High Density Polymer) process.
To repair Ft. Worth's storm drain, Uretek ICR's approach was to determine the failure locations in the soil and fill those voids in the soil outside the perimeter of the pipe. Their patented polymer process integrates itself into the surrounding soils thereby filling, stabilizing and solidifying them. At the same time, the polymer seals any joints, holes, or other openings in the wall of the pipe, thus preventing any further inflow and infiltration. Since the entire bottom of the pipe was corroded and compromised, the bottom had to be reinforced in conjunction with the other steps. Uretek ICR chose to replace the bottom of the storm drain with overlapped galvanized steel plates, 8 feet long by 6 feet wide, beginning work at the outflow end of the pipe and working back toward the headwall. The galvanized plates are anchored with two rows of zinc-coated screws spaced 12 inches apart. The headwall plate acts as both an anchor and a transition piece to allow a smooth flow of water from the corrugated pipe onto the galvanized steel.
David Finley, who specializes in infrastructure repair for Uretek ICR, described the process. “Once we got our first anchor plate down, part of the crew used an all terrain vehicle and a trailer to haul the steel into the 78-inch diameter pipe and lay down each steel plate. Other crew members then set the pipe and screwed the plates down. Behind them a crewman was injecting our two-part polymer using our patented deep injection process through predrilled holes in the plates, injecting it deep into the soil underneath the storm drain, subsequently sealing each 20-foot joint under the steel plates to stabilize the soil and force out free water, completely filling all voids in the soil for a solid foundation.”
The procedure requires a proprietary product that is hydro-insensitive, meaning that it repels water and it does not require air or water to react or expand. Uretek ICR's high-density, high-strength polymer material can support massive loads and mixes well with underlying soils to insure soil stabilization while filling all voids and displacing free water.
“The product that we use is a URETEK 486 Star two-part expanding polymer which is injected through rods which are drilled down to the required depth and start our deep injection process,” Finley said. “It's chemically reactive; it does not require water or air, and it's 95 percent cured within 15 minutes.”
In addition to Uretek ICR's patented products, Uretek ICR used chemical grouting compounds to seal the corrugated openings in the pipe after the steel was laid down, and any area above the valleys in the corrugated pipe was sealed with chemical grout.
Finley said that, “When you walked through the pipeline before we fixed it, you'd fall through rotted galvanized pipe, sometimes as deep as 3 feet, but now the floor is solid and you can walk the full distance of the pipeline.”
The 100-foot section of storm drain that the city of Ft. Worth replaced with reinforced concrete pipe cost approximately $70,000. Total distance of the pipeline is 1,000 feet, so if the rest of the 78-inch-diameter storm drain had been repaired the same way, the whole job could have easily cost over $700,000. Uretek ICR repaired the remaining 900 feet of pipeline in the last week of August 2008 for only $148,500 – well below the city's budget.
Six Uretek employees and the owner of the company worked on the job, and David Finley said that “It was an extremely streamlined operation which went a lot faster than expected. I thought it would take two weeks and the city allotted us three weeks, but it only took us four days. The city of Ft. Worth's goal was to get 10 more years from the pipeline, but we think that they'll now be able to use the pipeline for a lot longer than that.”