Like most structures, bridges are designed for an array of loading conditions. Some loads are known or can be reasonably estimated with confidence (i.e., known-knowns, such as structure dead and vehicular traffic loads). And based on site conditions such as regional seismicity, scour-prone foundation sediments, or downdrag loading from settling foundation soils (i.e., known-unknowns), load conditions can be estimated, albeit with less certainty. But on occasion, a bridge can be affected by a load condition that no designer could have anticipated (i.e., unknown-unknown). This story is about such an occasion.
Sy, A. 2019. “An Unknown-Unknown Does in an Overpass: A Soil Stockpile on Soft Clay Is Too Much for a Bridge in Canada.” GeoStrata. 2(23): 62-67.