EFFECT OF WALL CORROSION AND BACKFILL EROSION ON THE STRENGTH OF DETERIORATED METAL CULVERTS

While inspection technologies and assessment methods are being developed for corrugated metal culverts and sewers by researchers and specialized contractors, there is a dearth of information on how the level of corrosion influences culvert stability, and the possible consequences of backfill erosion. Therefore, work is needed to make the connection between an assessment of pipe condition and structural stability. This manuscript outlines recent findings from two and three dimensional computer studies of corroded metal culvert stability. First the article explains and quantifies how wall loss by corrosion across the invert of the pipe influences the thrusts and moments that occur in the structure, how this changes stability against yield, and how it changes resistance to global buckling. Next it examines the impact of backfill erosion resulting from groundwater inflow through wall perforations. This loss of soil support influences expected thrust and moment, and resistance to yield and global buckling. Lastly, the impact of wall thinning on resistance of the corrugated plates to local buckling is examined. The study indicates that wall loss has little influence on the hoop thrusts in culvert wall, so that reductions in stability against crushing are a linear function of the percentage of wall area that remains to support the thrust. Three dimensional analysis reveals that average rather than minimum wall thickness controls stability at any circumferential position, and buckling calculations indicate that wall thinning has little effect on global buckling strength until almost all the wall has been removed. Erosion can actually reduce thrust levels, but global buckling resistance is dramatically reduced. Furthermore, local buckling can occur for corrugated plates where thickness reduces below 3mm.