Traffic is routed around a portal work area in a major thoroughfare in downtown La Mesa, Calif.
When the San Diego County Water Authority installed major sections of 66- to 96-inch diameter pipelines in the 1960s, 70s and early 80s, the regional water wholesale agency used cost-saving pipeline material — a combination of steel wires, thin steel pipe, and concrete widely known as pre-stressed concrete cylinder pipe (PCCP). Decades later, agencies around the globe realized that some pre-stressed concrete cylinder pipe didn't last as long as advertised and could fail catastrophically.
The Water Authority deployed a multi-faceted response using high-tech asset management tools to identify pipeline sections with the greatest risk of failure and a targeted pipeline relining strategy that minimizes community impacts during construction. The agency's relining program started in the 1980s and ramped up in the early 2000s, so that today it is on track to complete more than 45 miles of relined pipeline in the next few months.
The current project is taking place deep below the urban streets of La Mesa, Calif., where the Water Authority and its contractor, L.H. Woods & Sons Inc., are on schedule to conclude by summer 2018. The delicate, 4.3-mile operation started in September 2017 after years of cross-departmental preparation to ensure the work on the $28.6 million contract could be completed in a cost-efficient fashion without impacting water deliveries.
Instead of trenching and removing the old pipe, crews are excavating 13 entry portals at strategic points, then inserting steel liners into the pipeline using a specially designed cart. When the pipe installation work is done, the portals are backfilled, the streets are repaved, and the pipeline is put back in service for at least another 75 years — at about half the cost of a conventional pipeline replacement project.
Looking for Weak Spots
To identify sections of its 310-mile, large-diameter pipeline system that require relining, the Water Authority relies on a suite of high-tech monitoring tools that are part of its pioneering asset management strategy.
Weak spots are often first detected with a "PING!" indicating a snapped steel wire in the PCCP. That sound is relayed through acoustic fiber optic cables — installed as an early warning system inside pipelines — so that Water Authority staff can be alerted by email and cell phone. Each ping is matched with results from Remote Field Eddy Current assessments and visual inspection data, then mapped using Google Earth.
With that information, pipeline segments are plotted on a risk matrix showing the condition and impact of failure. The sections with high risk and high consequence of failure are prioritized for upgrades. On occasion, emergency repairs are required where failure is imminent and the risks are significant. Other, less risky sections continue to be monitored and managed to maximize their service life. This risk-based approach has allowed the Water Authority to avoid more than $200 million in infrastructure spending.