An Unknown-Unknown Does In An Overpass: A Soil Stockpile on Soft Clay Is Too Much for a Bridge in Canada

by Alex Sy, P.Eng., Ph.D., (M.ASCE), Vice president, technical at Klohn Crippen Berger in Vancouver, BC, Canada.,,

Serial Information: Geo-Strata —Geo Institute of ASCE, 2019, Vol. 23, Issue 2, Pg. 62-67

Document Type: Feature article

Abstract: 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.

Subject Headings: Soft soils | Bridge design | Seismic loads | Overpasses and underpasses | Clays | Bridges | Load factors | Dead loads | Canada


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