A portion of the CANAMEX North-South Trade Corridor being constructed by the Province of Alberta includes a ring road around the city of Edmonton. The road, which is referred to as Anthony Henday Drive, includes crossing of the North Saskatchewan River in the southwest corner of the city. Tetra Tech’s geotechnical team provided expertise in slope stability and instrumentation for this project.

The short-term design for the 360-meter-long bridge crossing the North Saskatchewan River included two lanes in each direction; the ultimate design includes a total of eight lanes. Significant approach fills for the proposed bridge structures were required on both sides of the river. Based on the proposed vertical alignment, the maximum difference in height from the crest of fill to river level is approximately 35 meters on the west side and 28 meters on the east side. These fill heights are among the highest in the Edmonton area.

Tetra Tech was retained to assess the bridge headslope stability, which was a major issue because the clay shale formation at the base of the river valley contains bentonic layers and is subject to pre-shearing. The contractor constructed the test fill that Tetra Tech recommended to better assess the response of the underlying bedrock. The Tetra Tech team then monitored both the pore pressure and slope movement. Prior to fill placement, Tetra Tech installed pneumatic piezometers in the native floodplain deposit and in the underlying bedrock. Our team also installed vertical inclinometers near the toe of the vertical test fill to a depth of approximately 20 meters into bedrock.