Spray-applied lining proactively protects an aging set of drainage lines from catastrophic failure and potential roadway loss.
Fearing that disintegrating structural integrity could lead to the loss of a roadway, the asset owner called in Pleasants Construction of Clarksburg, Maryland, to inspect a set of twin 108-in. diameter storm drainage pipes showing early signs of deterioration. The asset owner had experienced prior failures in lines of similar condition. They asked Pleasants for recommendations on how best to immediately rehabilitate the structures, to prevent a potential catastrophic loss and even the complete washout of the road.
The 196-ft structures were situated on an embankment running behind and between residential properties, and beside a main throughway in a small rural development. One of the pipes served as an overflow, the other carrying a small stream through it.
The 108-in. diameter corrugated metal pipes had been originally installed sometime in the 1970s. As with most storm drainage pipes of this type, time had taken its toll: Rust had eaten away areas of the surface inverts; debris had built up; and expected deterioration of the structure due to age was present.
“Although they were not one of the worst that Pleasants Construction has rehabilitated, it was typical of something that, if let go a few more years, it could become a catastrophic failure,” shares Pleasants Construction project manager Ryan Smith.
Water was diverted from the one pipe to the other using steel plates. The area was sandbagged off so that minimal pumping was needed, leaving just a small amount of water inside. This allowed the crew to work in one pipe at a time.
Structural loss was complete in some areas of pipe. Pleasants brought in a subcontractor to install a concrete paving insert along the entire bottom of the pipeline, to reinstate full flow function. They designed the paving to divert the streamline from the influent side over to the effluent side, and created a channel that was somewhat squared up. It tapered to the edge above where the rust line occurred. In some areas, the concrete application was higher, to cover up any rough spots.
Once the concrete was set, the crew used sandblasters to remove any old metal deterioration and rust, to create a clean surface. In areas where infiltration was found, injection grouting was performed. Depending on the nature of the infiltration, groundwater and ambient temperature, as well as the severity of the infiltration — slow or fast leak — several different grouting products from Avanti and OBIC Products were used.
As a seasoned trenchless rehabilitation company, Pleasants is aware that the secret to successful rehabilitation involves three factors: prep, prep, and more careful, thorough prep.
Once the initial concrete profiling and surface cleaning were performed and injection grouting had set, the crew set up fans to make sure the pipe surface was completely dry, to properly receive the lining application.
This posed a challenge, as the rehabilitation was performed in the fall. In this part of the East Coast, condensation and moisture on autumn mornings can be problematic. When dealing with a structure of this size, heaters would not be enough to remove that moisture. Success would be more about airflow (the volume of air running through the structure) to achieve the needed desiccation.
Once the surface was dry, crews began the application of OBIC 1200, a spray-applied, plural-component polyurethane from OBIC, LLC. The coating is formulated for storm drainage and culvert applications. OBIC offers various choices of lining, including a structural formula; but since structural issues had already been addressed with the concrete installation and injection grout, the culvert product would be sufficient for a successful rehabilitation at less cost.
OBIC 1200 was applied as a single layer, to a thickness of 150 mils. Application of the lining on the first pipe was accomplished in approximately seven days. In total, the process of the first pipe’s rehabilitation was approximately 10 days.
“Because of all the condensation and prep work on the first line, it was decided that the rehabilitation using the same method for the other half of the twins would be completed in the spring, when weather conditions were more favorable and application could be performed in a shorter period of time,” explains Smith.
During the first pipe’s lining installation process, as the team was spraying, additional leaks began to appear in the pipe that had not been spotted earlier. Production was halted, in order for prep and injection grouting to be completed before spraying could recommence. Seeing that this could be a pattern on the next segment of pipe to be rehabilitated, the crews decided they would get out ahead of time — in March — in advance of mobilizing the spraying crew and sandblasting equipment in April 2021, as planned.
Once the spray application was completed, quality control testing was performed. The asset owner was impressed with the method, product, and how quickly the rehabilitation was able to be completed. The advantage of spray lining for such applications is its quick return to service.
In this case, within 3 to 5 seconds after spraying, the product was tack-free, and the lined area could be returned to service in approximately 60 minutes. As a result, Pleasants is looking forward to utilizing spray-applied rehabilitation methods on other large structures, such as a new project to rehabilitate an overflow pipe that is 38 ft wide by 22 ft high and several hundred feet long.
“We have the ability to utilize many different trenchless rehabilitation technologies such as UV GRP lining, but in these larger structures, spray-applied lining is proving itself to be a great choice because of its many advantages for protecting against potential failures and giving us the ability to quickly resolve issues and put assets back in service with minimal disruption for our clients,” says Smith.
Suzan Chin-Taylor is CEO of Creative Raven. Photos courtesy Michael Hoffmaster.