The City of Toronto’s Gardiner Expressway serves as the main artery into the City, stretching 11 miles from the Don Valley Parkway to the Queen Elizabeth Way (QEW). In operation since 1955, the Expressway has long been the topic of much debate: structural concerns have resulted in recommendations that sections of the Highway be rehabilitated and in some cases, replaced.
To get an accurate picture of the Expressway’s condition, a solution was required that could map bridge deck deterioration over a vast area. The solution would need to be capable of collecting reams of surface and subsurface data which could subsequently be analyzed, mapped and used to make informed decisions around rehabilitation and replacement.
With traffic gridlock costing the City of Toronto an estimated $7-$11 billion annually, it was critical that the data collection process have a minimal impact on traffic flow.
Solution – mapping bridge deck deterioration
To inspect the vast and geometrically complex structure, Ground Penetrating Radar (GPR) was applied to analyze all continuous east and west bound lanes of a 6.1km raised section along with corresponding access ramps. High-resolution GPR observations were collected from curb to curb, less than a metre apart at a speed of 40km per hour. Six lines of data were captured for each vehicle lane and over 1.3 million targets within the project area were processed and georeferenced to assess deterioration. Data was then digitally recorded to produce colour-coded contour maps for each section which were included with a detailed evaluation report.
The data were also used to create a bridge deck deterioration index that indicated the percentages of each section appearing to be above the deterioration threshold. Methodology prescribed by standard ASTM D 6087–08 was leveraged and augmented by depth compensation to account for existing inconsistencies along the bridge deck. To ensure accuracy, data was also correlated with known structure information such as existing coring data and OSIM inspection records. With over 200,000 commuters relying on the Gardiner Expressway each day, GPR made it possible to acquire data with no measureable impact on traffic flow.