Performance Data Collected from Instrumentation on a Mn/DOT Bridge Abutment Foundation Subject to Downdrag

A recent Minnesota Department of Transportation bridge project was outfitted with two in-place inclinometers and a series of strain gages on two driven piles to measure the change in strain, and associated stress, as consolidation settlement occurred in cohesive soils below newly placed bridge approach embankment fill. The magnitude of the downdrag acting on the piles, corrected for thermal effects, was monitored with respect to construction loading stages and nearby soil deflection. Downdrag loads of as much as 445 kN (50 tons) per pile were anticipated in the original design. Use of frequent data collection at this site, combined with the benefits of the construction sequencing - bridge loads were applied well after the construction and short-term surcharging of the embankment fill occurred - has offered additional insights into pile behavior in a downdrag environment. The paper discusses some aspects of the data collection and observed time-domain behavior of a selected gage location over a year-long observation period. A more comprehensive case history of this project, including overall pile behavior, and an investigation of the effects of the use of `pile sleeves' and live load dynamic response is in development for future publication.