Subject and Keywords:
Tests conducted in the GeoEngineering laboratory at Queen’s examined the ultimate strength of buried circular and elliptical metal culverts under shallow cover. A circular culvert of 0.9 m diameter at cover depth of 0.45 m responding to a single wheel pair load at the ground surface over the crown was found to have strength controlled by full plastic moments developing at the shoulders and crown. This failure mechanism is different to that addressed in the AASTHO standards (which examines springline thrusts), and it occurred at loads lower than the required load capacity. Testing of a horizontal ellipse of 1.6 m span and 1.35 m rise was also conducted at 0.45 m of cover, but under simulated tandem axle loading. This structure also had strength controlled by bending at the shoulders and crown. Comparisons of experimental thrusts were made to estimates based on AASTHO design equations. These demonstrated that the maximum live load thrusts observed in the culverts at 0.45 m of cover were 136% and 197% of the AASHTO design estimates (for the circular and elliptical structures, respectively), while design estimates of thrust for cover of 0.9 m were reasonable and conservative compared to the experimental observations at that greater depth. Further study is recommended with the aim of either defining minimum burial depths for which AASHTO design can be employed, or changing the design equations for estimating thrust demand and introducing consideration of flexural limit states for small span corrugated steel pipes at shallow cover.