Installed Geometry of Cast-in-Place Polymer Sewer Liners

Polymer liners cast within damaged sewer pipes are commonly used in rehabilitation without the disruption associated with conventional trench excavation and pipe replacement. Linear stability depends on both the thickness of the liner, and any out-of-roundness (ovality or other shape imperfections). Field trials of four cast-in-place liner systems permitted samples to be exhumed and inspected. Measurements of liner thickness and out-of-roundness are presented, for use by researchers and others seeking to establish the stability of these pipe repairs. Significant variations in thickness were observed. These took the form of wavelike increases in local thickness. For all four types of lining systems, the maximum thickness was more than double the average thickness, and up to three times thicker than the minimum thickness values. Higher frequency thickness variations were also superimposed on those wavelike changes in wall dimension. Liner ovality of up to 10% was also observed due to ovality in the clay sewer pipes being repaired, even though those pipes were not fractured longitudinally. Postconstruction inspection of liners ideally includes assessment of liner thickness. Wavelike increases in liner thickness might be estimated, where these lead to intrusions into the waterway. However, irregularities on the external surface of the liner or long wavelength thickness variations would be impossible to detect from video inspection alone, and new inspection techniques are likely need to be developed to ensure the installed liner performs successfully over its design life.