Experimental Evaluation of Two Lining Methods Used for Pipe Rehabilitation

Abstract

The goal of this research is to investigate two trenchless rehabilitation techniques, with the objective of developing a better understanding of potential failure mechanisms. The first experimental study involved the testing of two spray-on polymer liner materials (epoxy and polyurethane) that are applied to a concrete substrate to prevent leakage. The concrete specimens had circular plastic sheets attached to simulate areas of de-bonding before being sprayed with the liner. External water pressure was applied to the underside of the polymer liners to investigate the effect that the areas of ‘de-bond’ had on the failure pressure needed to induce tensile fracture of the polymer or peeling failure between the liner and substrate. The epoxy liner failed in tensile fracture while the polyurethane liner underwent peeling failure. Regardless of the failure mode, increasing the de-bonded area resulted in a lower failure pressure. It was also found that the tensile fracture strength can be conservatively estimated using flat plate theory. Additionally, it is suggested that peeling force can be related to adhesion strength, but only for similar liner-substrate systems. The second experimental study investigated the response of a slip-liner to increasing fluid pressure, as would be experienced in a grouted slip-liner procedure. An experimental apparatus that enabled fluid pressure to be applied to the liner was developed and used to complete two tests on a PVC liner. The liner was tested in a vertical orientation to investigate the liner’s response to axi-symmetric fluid pressure while a horizontal test investigated the response to buoyancy loading coupled with fluid pressure. Each test was run until the critical buckling pressure was reached, marked by the formation of a buckling lobe. Bending moments were positive at the springlines and negative at the crown and invert as expected, and increases in thrusts at each 25 kPa load step showed good agreement with theory. Hydrostatic buckling pressures of the PVC liner were within -7% of the theoretical buckling models (using mean thickness), while peak critical liner buckling pressures were overestimated by +16% to +25%, implying that further work is required to extend the design theory to cover more geometries.