For some time, trenchless installation methods have permitted lining of gravity flow sewers and culverts, restoring both hydraulic and structural integrity. However, it was not until recently that Sanexen of Montreal developed the first cast in place liner to repair Cast Iron water pipes. This innovative system permits lining, then reopening of customer connections using a remote controlled robot. This system is growing in use across North America.
A review of the system for Hamilton City in 2004 revealed that wrinkles can form in these composite liners. Nancy Ampiah developed procedures to test the strength of wrinkled liner specimens cut from samples exhumed after the field trial in Hamilton. Resin fracture occurs first, and leads to reductions in hoop stiffness of the composite liner. These fractures invariably occur in the vicinity of the wrinkle. Loading rate had no effect on cracking load for the liner, but sustained load reduces the ultimate strength of the liner system. All liners tested had strength sufficient to resist the design loads.
Nancy developed finite element models of the composite liner, with explicit representation of the textiles at the inner and outer surface of the liner, and the resin within. These models were used to investigate locations of stress concentration, and explore the ability of the analysis to model how wrinkle shape and size influence behaviour. Fracture in the resin corresponded to stress concentrations in the finite element analysis.