Foundation Design and Embankment Reinforcement for the McOrmond/College Drive Interchange

The Saskatoon Interchanges Project consisted of design-build construction of two grade-separated traffic intersections. As part of the design for each interchange, approach fills of approximately 8 to 9 m height were required at all four abutments for the two bridges; 5 m high mechanically stabilized earth (MSE) walls were incorporated into the design at each abutment. The soil conditions at each bridge location consisted of 10 to 14 m of firm to stiff clays (Saskatoon Group) or clay tills (Battleford Formation) overlying a very stiff to hard clay till (Floral Formation). The project agreement outlined constraints regarding long-term differential settlement of the approach fills relative to the bridge structure and MSE wall construction required limitations on the total magnitude of settlement. The relatively short construction period specified in the project schedule required that ground improvement measures be utilized to accelerate settlement rates for the approach fills. In order to meet the settlement criteria, and to address global stability requirements for the MSE walls, stone columns were incorporated into the foundation soils.

The initial design of the stone columns used a combination of design manuals and limit equilibrium analysis. A finite element deformation analysis was completed during detailed design to estimate deformations of the approach fill embankments and the MSE Walls. Construction of the stone columns was completed by drilling large diameter shafts which required the use of temporary sleeving to address seepage and sloughing conditions. After drilling, the shafts were then backfilled with a sand and gravel mixture and compaction targets were achieved through vibro-extraction of the sleeves. Settlement monitoring of the approach fills consisted of a combination of settlement plates, piezometers and survey monuments.

This presentation summarizes the design, construction, performance monitoring and lessons learned over the course of the project.