Underground Construction - October 2020 - 21

EDITION 61 | OCT 2020 | NASSCO.ORG
Keeping in mind that soil migration and loss of trench support of pipe are the main drivers
for external pipe failure and degradation of RUL, having a rehabilitation solution that
addresses these conditions as a part of its design is necessary to assure a long-lasting
solution. This can be seen across the spectrum of rehabilitation options, based on host
pipe condition versus the long-term need for both gravity (partially versus fully deteriorated
design conditions) and pressure pipe (Grade I, II, II or IV per the AWWA M28 standard). As
our understanding of deterioration mechanisms deepens, our design methodology will also
evolve as reflected in refinements to the design standards (see ASTM F2019-20 and the
recommendation for use of the Modified-Glock buckling analysis).
Our challenge with design standards, no matter how reliable and well understood, is
resolving the confusion between a robust design life versus actual RUL. The confusion
lies in the assumption that a 50-year design for wall thickness, liner thickness or coating
thickness based on an
assumed reduction in
materials strength of the
rehabilitation solution is an
implied guarantee about
the RUL of the product.
Unless stated specifically
by the installer or supplier, most warranties are for one year, and the design is based
on performance assumptions that may or may not reflect actual installation conditions.
Additionally, the first CIPP was installed in the early 1970s, so we are just now able to
validate a 50-year service life of installed trenchless rehabilitation solutions.

"The initial declaration of a design life
for gravity sewer CIPP came out of
marketing, not engineering."

So how does PACP™ address trenchless rehabilitation and where are we headed
with assessing RUL of rehabilitation solutions? PACP has Lining Feature (LF) group
observations that provide visual assessment of mostly CIPP solutions. As Grade 3 structural
observations, they imply conditions that could compromise the effectiveness of the new
pipe, but do not offer an assessment of reduced RUL. Though insightful, this visual
assessment should be coupled with testing of pipe coupons and inspection documentation
of the installation to assess its long-term effectiveness. Bottom line is that RUL for
rehabilitated assets is an assumption based on confidence in the design standard, qualified
manufacturers and installers, and a commitment to quality assurance and quality control
measures to assure that the installation meets the industry standard of care.
NASSCO will be presenting a webinar on RUL in the coming months. Please look for
forthcoming information and join us as we further explore this topic by visiting NASSCO.org.

TECH TIPS IS A BI-MONthly article on
trends, best practices and industry
advice from NASSCO's Trenchless
Technology membership PROFESSIONALS
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Underground Construction - October 2020

Table of Contents for the Digital Edition of Underground Construction - October 2020
