Applied Research Turns Wire Breaks into Innovation Opportunity for GLWA

Following the 2017 catastrophic break on Great Lakes Water Authority’s (GLWA) 14 Mile Road transmission main, GLWA conducted a wet-live electromagnetic (EM) inspection of 9.3 mi of the prestressed concrete cylinder pipe, which was installed between 1967 and 1973. The EM inspection evaluated all 2,623 pipes along the alignment, which ranged from 60-, 54-, 48- to 42-in. diameter, and identified 100 distressed pipes (a distress rate of 3.8%) with broken wire wraps. One 650 linear foot segment of the 54-in. diameter portion of the alignment had a much higher distress rate of nearly 50%, including several severely distressed pipe segments. Plans for renewal of this distressed section of pipe were made using carbon fiber reinforced polymer (CFRP). The GLWA’s Energy, Research and Innovation group, along with Field Services and the Linear System Integrity Program, made plans to leverage this area of known damage for evaluation and piloting of four different emerging technologies for monitoring and assessing prestressed concrete cylinder pipe (PCCP). Each technology would assess or monitor the same section and the pluses and minuses of each technology would be evaluated in true field setting. First, discrete acoustic sensors were installed at three existing access point manholes along the distressed segment to provide an economic and non-intrusive approach to monitoring for broken wire wraps prior to installation of the CFRP renewal. Second, during the CFRP renewal project, high-fidelity optical sensing fibers in metal tubes (FIMT) were installed (embedded within the CFRP system) to evaluate the advantages and capabilities for each method of measuring pipe structural health. Post-installation of the CFRP, two “outside the pipe” technologies were evaluated, each using external excitations to the pipe wall, with the pipe in service used to assess the pipe condition. The first technology utilized acoustic velocities to calculate the effective pipe stiffness and the effective-to-nominal stiffness ratio for each inspected test segment. The second technology evaluated structural condition of individual pipe segments using the dynamic response of the pipes to excitations at different frequencies. Each piloted technology had advantages and disadvantages. This paper documents the overall implementation as well as applicability of each technology to assessing the condition or monitoring the structural health of PCCP.