Jason Luty, Nilex Inc.; John Kerr, Tensar International; W. Campbell, Graham Construction & Engineering;J. Halford, City of Calgary
Increased pressure on urban transportation infrastructure has led owners, engineers and contractors to utilize more innovative solutions in both design and construction.
An example of the need to meet economic and time restraints is the upgrading of Glenmore Trail west of MacLeod Trail in Calgary, Alberta – the largest project undertaken by the City of Calgary in it’s history. In order to relieve traffic congestion in this busy section of the City, the alignment of Glenmore Trail was lowered up to 9.0 meters below surrounding grade. The project extended from Macleod Trail west to 14 Street SW, a distance of approximately two kilometres. The lowered alignment enabled the east-west traffic on Glenmore Trail to pass under the north-south street system without interruption. Mechanically Stabilized Earth (MSE) retaining walls with a total face area of 16,000 m2 were provided along the north and south sides of Glenmore Trail to facilitate the grade differential. Three bridges and a pedestrian overpass were also constructed using MSE abutments.
Challenges facing the project included highly variable foundation soils as well as a water table above the elevation of the retaining wall foundations. The design and construction of a permanent drainage system was required to meet this challenge. The complex street alignment had to be built within a tight corridor between the properties on the north and south sides of the project. Allowances also had to made to permit east-west traffic as well as to provide unobstructed access to the large shopping center bordering the north side of the project. The geogrid anchors used to support the MSE wall face had to be designed to be as short as possible at the same time as maintaining acceptable design safety factors. The tight geogrid design was carried out using variable geogrid lengths designed using trapezoidal cross section design procedures. In some cases, foundation shear keys were also installed to allow for realistic geogrid anchor lengths.
The tight construction schedule required earthwork and construction of the retaining walls to carry on, uninterrupted, throughout the winter months. Wall construction began in the summer of 2005. The construction schedule was met and the project was substantially completed, within budget, in November of 2007.