Establishing a Quality-Control Program for Lateral CIPP Repair

Surrogate samples for lateral CIPP projects help Ontario city maintain standards.

Establishing a Quality-Control Program for Lateral CIPP Repair

Workers create a lateral sample on the job site using a thermocouple to monitor the temperature and ensure a comparable proxy.

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As the popularity of trenchless lateral rehabilitation continues to grow, so does the need for cost-effective quality-control measures for CIPP repairs on the private side.

Like many other cities throughout North America, the city of Hamilton, Ontario, has found a proactive rehab program for sewer laterals is preferable to costly and reactive opencut repairs. The city first developed its lateral rehabilitation program in 2008, has renewed its contract multiple times and, as of 2017, has repaired more than 4,600 laterals. The CIPP liners used for these projects are required by the city to be one-piece lateral liners including sewer connections.

While the program has advanced and adapted since its inception, quality control remained a challenging facet of the strategy due to the difficulties and costs associated with collecting samples.

That’s why Robinson Consultants — working with the city and its contractor — came up with quality-control procedures including a “proxy” sampling method and presented its methodology as a white paper titled “Quality Control for Sewer Lateral Rehabilitation” at the North American Society for Trenchless Technology’s No-Dig Show.

According to Robinson Consultants, collection of CIPP samples from an actual installed liner is challenging, unless you’re planning on excavating a portion of the lateral. Meanwhile, the practice of quality-control sampling remains as important for laterals as it is for sewer mains.

The proxy method

The city of Hamilton, like other municipalities, uses CCTV video inspections after cleaning and preparing a lateral, and again after liner installation. But for long-term quality-control data, it’s now using a proxy method by which it creates aboveground samples using 2-meter lengths of PVC at an actual installation site using the same resin, tube, curing method and installation procedures as the true installation. Especially in colder outdoor air temperatures, the city recommends using an insulation blanket to help simulate an underground environment when creating the proxy sample.

After a sample is completed, it’s cut in half and both the utility and contractor keep a sample for records, which offers the ability to perform primary testing and, when necessary, secondary testing. The samples are identified with the installation date, street name, contract number, contractor name, contractor crew, inspector’s signature and any special design requirements.

“In the case where sample test results indicate that the initial design requirements have not been met, further investigation is undertaken to determine if the liner will still perform adequately within the specification requirements for the particular installation,” according to the white paper.

In addition, the city of Hamilton requires contractors to keep installation records for each project including street name; liner size; mix ratio; resin lot numbers; resin volume used; roller separation; inversion pressure; cure pressure; resin mix time; resin gel time; and cure temperature, including exothermic temperature, truck temperature, ambient temperature at the invert of the mainline sewer manhole, steam temperature, water temperature and outside weather temperature.

While the contractor notes all the above information, a city inspector also conducts his or her own site inspection to provide an audit record of compliance.

“The information collected in these installation records holds significant value when analyzing the overall quality of lateral liner installations and in determining the cause (or most likely cause) of sample test failures,” reads the white paper. “Without installation records, the ability to monitor installation quality and take corrective action in a timely manner is significantly reduced.”

Testing samples

When it comes to testing its samples, the city of Hamilton provides a testing agency with design parameters for flexural strength, flexural modulus and original design thickness. The city tests about four or five CIPP samples on a monthly basis and reviews them against the liner design, project specifications and overall trends in three test criteria — flexural strength, flexural modulus and design thickness.

“It is important to recognize that trend analysis is far more important than just the individual test results because samples are not taken from the actual installed liner, but rather independently created,” according to Robinson Consultants.

If an initial review of a test report finds any problems associated with the three testing criteria, that triggers a secondary review that establishes whether the liner can still meet its performance standards for its specific project.

The city tracks those results in spreadsheets over time to give a sense of trends, and it uses that data to create easy-to-read lateral sample trend analysis charts that include ambient air temperature in addition to flexural modulus and thickness.

Being able to see these trends over time has helped inform the city of Hamilton’s ongoing lateral relining projects and give it confidence in liner performance.

“While the quality control of lateral CIPP installations is more challenging than mainline sewer CIPP, it is equally important in establishing that the installations are achieving the required performance,” reads the white paper. “As with all trenchless technologies, continual improvement in the processes and methods in the use of CIPP continues to evolve. It is vital that the same level of effort is put toward the processes and methods for their quality control.” 


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