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Applications of Pipe Penetrating Radar for Advanced Pipe Condition Assessments: the Clark Regional Wastewater District (WA) Case Study

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Abstract
Pipe Penetrating Radar (PPR) is the underground in-pipe application of GPR, a non-destructive testing method that can detect defects and cavities within and outside mainline diameter non-metallic (reinforced concrete, vitrified clay, PVC, HDPE, etc.) underground pipes. The key advantage of PPR is the unique ability to map pipe wall thickness and deterioration including voids outside the pipe, enabling accurate predictability of needed rehabilitation or the timing of replacement. By having this information available, engineers and municipalities can better estimate the remaining life left in a pipeline, refine timing of repairs, and ultimately better allocate funding for asset management.

This paper presents recent advancement of PPR inspection technology together with the robotic, Vancouver, WA case study. Clark Regional Wastewater District, the owner of the Salmon Creek Interceptor and St Johns Trunk lines commissioned a condition assessment on the 21, 24 and 36 inch concrete lines. For the St. Johns Trunk, a 36-inch line, corrosion was suspected and evidence was observed visually by CCTV. Chemical dosing had been implemented to minimize continued corrosion due to vapor-phase H2S, but the District wanted to quantitatively determine the extent of corrosion and if/when future rehabilitation would be needed. PPR confirmed the upstream-most segment had corroding/missing reinforcement and reduced wall thickness.

For the Salmon Creek Interceptor, 21-inch and 24-inch lines, visual CCTV inspections revealed the inner cement layer had deteriorated. In these pipe sizes, the District was unsure if these pipes had reinforcement. PPR was used to determine changes in wall thickness and if reinforcement was present. The PPR results confirmed that the 21-inch concrete sewer was unreinforced and the observed corrosion had structural implications. The 24-inch segment was reinforced and had uniform pipe wall thickness with sufficient rebar cover. Subsequent coring improved the velocity calculations for the 21-inch and 24- inch pipe and confirmed and verified the PPR pipe wall thickness.

With limited available funding and budget constraints becoming more prevalent, timing of rehabilitation and overall intelligent asset management is more critical than ever. Advanced pipe condition assessment technologies, such as PPR show promise as a cost-effective, non-destructive method of condition assessment to help refine the estimated remaining life of a pipe, accurately determine pipe degradation, as well as provide a basis for improved cost allocation and timing of rehabilitation efforts.

Key words: pipe penetrating radar, PPR, condition assessment, non destructive testing, asset management, pipe inspection

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