A History of Foundation Engineering in Windsor, Ontario, and Developments in Prefabricated Vertical Drain Design

Subsurface conditions throughout Windsor, Ontario, Canada, are characterized by deep, compressible clay deposits within the physiographic setting known as the Essex Clay Plain. The consolidation characteristics of these deposits have been widely documented, and geotechnical engineers have been refining best practices over the years to estimate ground settlements at bridge sites. This paper provides a history of these best practices by summarizing the investigation, design, and monitoring methods employed at 15 bridge sites constructed on compressible clay in Windsor, Ontario. Of these 15 bridge sites, 14 of the bridges were constructed in the 1950s and 1960s and were part of a 2006 settlement study. Construction of the fifteenth bridge site was completed in 2023 as part of a Design-Build Contract. The construction methods used at the fifteenth bridge site illustrate the advancements in foundation engineering since the 1950s and 1960s through the installation of prefabricated vertical drains (PVDs or “wick drains”). PVDs have become a desirable option to accelerate consolidation, reduce the construction schedule, and save costs for bridge sites founded on compressible clay throughout Ontario, Canada. The paper concludes with the back-calculation of a key PVD design parameter known as the “smear ratio” using construction monitoring data collected during construction. The determination of the smear ratio and comparison with the values used for other PVD sites support the premise that the parameter is site-specific and that continued collaboration and assessment of best practices by geotechnical engineers is necessary to continue advancing the field of foundation engineering in the region.