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Ultimate Strength Testing of Two Deteriorated Metal Culverts Repaired with Spray-On Cementitious Liners

Two deteriorated corrugated steel pipelines were buried in the west test pit at Queen's University and then repaired with spray-on cementitious liners with target liner thicknesses of 3 in. (76 mm) and 2 in. (51 mm), respectively. After service load testing described elsewhere, tandem axle loading was applied at the ground surface over each of the rehabilitated culverts; forces up to and beyond fully factored loads were used that brought the culverts to their ultimate limit states, evident by the development of both longitudinal cracks along the crown and invert of each structure, as well as circumferential (ring) fractures at various locations. The repaired pipes were then exhumed and measurements made to characterize the actual (as opposed to nominal) liner thicknesses achieved by the repairs. The level of composite interaction between the liners and steel pipes was also examined. Ultimate load testing at cover depth of 4 ft (1.2 m) induced the first signs of liner cracking at tandem loads of 180 kips (800 kN) and 145 kips (650 kN) for Pipelines 1 and 2, respectively. Circumferential cracks were observed under the wheel pairs and near the midpoint of the axle. Mean liner thicknesses were found to be 2.5 in. (64 mm) for Pipeline 1 (84% of the target thickness) and 1.7 in. (44 mm) for Pipeline 2 (87% of the target). Higher thicknesses were observed at the pipe crowns, and lower thicknesses were seen at the invert. Assessment of composite interaction during flexure of the lined steel pipes indicated that although full interaction was observed at some locations, only partial interaction occurred at other positions. Therefore, liner design should not rely on an assumption of a bond between the two components.