The Effect of Wall and Backfill Soil Deterioration on Corrugated Metal Culvert Stability

Abstract

Ministries and departments of transportation are working to undertake assessments of deteriorated metal culverts. To assist with these assessments by developing rational methods of classifying culverts, to select those requiring replacement or repair, the current thesis studied the effects of metal corrosion and backfill erosion on culvert stability. Finite element calculations were used to explain how stability is jeopardized by two forms of deterioration, both material failure (yield in the steel) and geometrical nonlinearity (bucking failure). The stability assessments are presented for structures designed using limit states design procedures in the Canadian Highway Bridge Design Code and the LRFD Bridge Design Code of the American Association of State Highway and Transportation Officials.

It was found that yield in culverts in intact ground is proportional to plate thickness (thrust and moment are not affected). Buckling strength changes as corrosion occurs, but does not become critical in structures supported by good quality backfill (without erosion). Surprisingly, thrusts decrease when erosion develops adjacent to the culvert, and this implies that factor of safety against yield is increased. However, substantial decreases in buckling strength occur, and elastic instability can then become the critical performance limit after erosion.

Three dimensional finite element analysis indicates that local buckling can develop before global buckling, for new structures featuring thin plates, or for thicker structures after corrosion. This form of elastic instability may not be safely estimated using current culvert buckling equations which consider global buckling.

Local buckling results were not effectively estimated using the Bryn’s equation (the conventional method used for stiffened plate structures); therefore a preliminary design equation for assessment of local buckling is provided.

After verifying the results obtained from this thesis with physical experiments, these findings can provide practitioners with useful evaluation tools for a quantitative assessment to the stability of buried culverts subjected to these two different kinds of deterioration (corrosion and erosion) in order to augment engineering experience or judgment, which is the primary tool currently being used. Moreover, the current study helps future experimental and numerical studies by investigating various significant deterioration scenarios, and the impacts of these scenarios.