EXPERIMENTAL INVESTIGATION OF THE STRUCTURAL MECHANICS AND PERFORMANCE OF CLOSE-FIT FLEXIBLE LINERS INSTALLED IN CORRUGATED STEEL STRUCTURES

Abstract

This thesis investigates the structural behaviour of corrugated steel culverts lined with cured-in-place-pipe liners under vehicle and hydrostatic loads through the conduct of full scale experiments. Further, with the tested structures, section and material properties of the liners are characterized and the relevant quality assurance practices are reviewed. The goal is to elucidate the mechanics governing the load resistance and capacity of these systems for the future development of design equations. Digital image correlation, electrical resistance strain gauges, string potentiometers, and fibre optic strain sensors were employed to study the behaviour of structures rehabilitated with two different liner materials: 1) a polyester filled felt and 2) a glass reinforced epoxy. Further, with optical fibre strain sensors, a new monitoring technique was prototyped and implemented to measure the response of the liner. Next, a study was undertaken to quantify the section and material properties of the two different CIPP liner materials. The results from the vehicle load studies demonstrate inadequacies in the present design guidelines for these structures, likely dependent on the closeness of fit between the liner and host pipe. Testing these structures up to their ultimate strength limits revealed that the liner-host-pipe-soil system may fail from either the host pipe forming a plastic hinge, or buckling of the liner. It was found that the cured-in-place-pipe liners reduced the peak curvature change and neutral axis strains that develop in the corrugated steel pipe due to vehicle loading by at least 39% and 43% respectively. The results from the hydrostatic load test, where external water pressure was applied to the felt liner, demonstrated that the application of the latest analytical models which account for ovaling and gap (Thépot 2021) may provide conservative approximations for the critical buckling pressure, deflection, moment, and thrust of the liner. The results from the section properties study demonstrated that both materials were close to if not more than the design thickness as well as quantified the thickness distribution and variability of the two liner materials. Further, sample size charts, have been developed and can be used to determine the number of measurements required to verify that the liner’s thickness is within some acceptable range of the design thickness for different standard deviation values. Finally, from the review of relevant material test standards, implementation gaps in the North American guidance are highlighted.