National Plant Services
When it comes to pipe rehabilitation, several options are available to asset owners: CIPP, Slip-lining, SAPL, FRPs, and Spiral Wound. Each method has advantages and disadvantages depending on the pipe being rehabilitated. The decision regarding which method is best depends on several factors such as pipe size, length, access locations, hydraulics, environmental issues, distribution to surrounding area, overall cost, operation of the system, bypass consideration and so on.
Spray Applied Pipe Liners (SAPL) are increasingly used for the rehabilitation of sanitary and storm sewers with pipes larger than 36 inches in diameter. Manufacturers can demonstrate technical performance data, verification testing, and design methodology using direct field data to show asset owners and the engineering community that this method has been vetted. It is a conservative approach that meets performance predictability requirements and ensures the system will operate for another 50+ years.
The City of Chula Vista in Southern California has used a geopolymer SAPL system on several projects with favorable results. The most recent project was on a 720 linear foot section of 66-inch CMP storm drain that experienced a rapid deterioration of the structure including the corrosion of invert, ovality of the pipe and ground water infiltration.
National Plant Services from Long Beach, California, was the successful lower bidder on the project after it provided a design thickness calculation, material to be used, verification testing reports and a list of past projects using the material, as required in the bid submittal package. This evidence proved to the City of Chula Vista that the pipe, once rehabilitated, would meet the city’s quality standards.
National Plant Services’ Project Manager Daniel Solano led the team that carried out the rehabilitation. The following steps took place:
New Manhole Installation
The city required two new manholes to be installed to allow for easier maintenance and inspection access. The manholes were cast-in-place, and the site was excavated down to the crown of the pipe. Formwork was installed in stages before backfilling upon completion of each section.
Cleaning the Pipe
There was a significant layer of debris covering the invert of the pipe along the entire length. Approximately eight cubic yards of material was removed.
Invert Repair
Cleaning of the storm drain revealed that the invert was severely corroded, with approximately one to two feet of the CMP pipe missing throughout the entire 720-foot reach. A new concrete invert was poured to fill the voids and bridge the gaps in the CMP pipe. Locally sourced 3,250 PSI concrete was used and allowed to cure.
Injection Grouting to Stop Infiltration
As typically occurs when an invert repair is made, water that used to flow under the failed invert can no longer escape the backfill and builds up around the exterior of the pipe. The water can then find its way through any gaps in the CMP pipe. Acrylamide grout is effective in stopping infiltration into pipelines, as it binds with the surrounding backfill to provide a waterproof collar around the outside of the pipe, preventing further infiltration. Manual grouting was performed by drilling holes through the pipe wall where infiltration was present and inserting an injection port to introduce the two-component grout mix. This mix fills the area behind the pipe, binding with the soil to stop future infiltration.
Spincasting of Geopolymer Structural Mortar Lining
After grouting was complete and infiltration was stopped, the pipe was ready for spincasting. The pumper/mixer assembly was placed near the access manhole along with pallets of pre-mixed dry material supplied in 50-pound bags. Concrete hoses were run from the pump into the manhole and through the pipe to the spinner sled at the far end of the pipe segment to be lined. The geopolymer dry mix was combined with a measured amount of water as it left the pump and traveled through the hoses to the spinner sled. A winch was used to pull the spinner sled back at a controlled speed to ensure the correct amount of geopolymer was released. Multiple passes, or lifts of material, are usually required to reach the design thickness, with an initial thinner lift often necessary in CMP to allow for better bonding of future, thicker lifts.
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