Wavy Imperfections and the Strength of Cast-in-Place Pressure Pipe Liners

The installation of resin-impregnated felt tubes within cast iron water pipes can lead to wavy imperfections (wrinkles) if the external circumference of the liner exceeds the internal circumference of the cast iron pipe. A split-disk test apparatus has been developed and a series of laboratory experiments have been conducted to measure the strength of liners with wavy imperfections. The design of the test apparatus is described, and results are reported for liners installed within cast iron pipes of six inch nominal internal diameter. Results for three different kinds of imperfections are provided, where measurements of maximum hoop force are related to the imperfection size (wavelength and amplitude). Most tests resulted in failures at or in the vicinity of the wrinkles. As the wrinkle size increased, the ultimate strength of the liner and its strength at first cracking were reduced. However, the effect was more detrimental on the latter than the former.