Highway 102/107 Overpass
Location: Halifax, NS
Client: Dexter Construction (Design-Build for NSDPW)
Time Frame: 2022-2024
Project Description
The Highway 107 / 102 Southbound overpass is a 3 span, 120.8 m long, curved trapezoidal steel box girder on a 145m radius, with semi-integral abutments and hammer-head piers supported on spread footings founded on competent bedrock located near Halifax, Nova Scotia. The project provides a new link between Highways 107 and 102 near Rocky Lake and the Bedford Commons. The bridge has a clear width of 10.0 m between TL-4 steel barrier rails mounted on top of 450 mm wide low profile concrete curbs, resulting in an out-to-out width of 10.9 m. The abutments and both in-median piers are skewed 25 degrees relative to the radial line. The abutments and piers were skewed relative to the radial line to reduce the spans and to mitigate disruptions on HWY 102 during pier construction. MSE walls are provided at the West Abutment to limit spans and overall project capital and life cycle costs, as well as allowing for the grade separation between the new western approach ramp and Highway 102 Southbound.
UPDATE: This project was awarded the 2025 the Steel Design Award for Excellence by the CISC in the category of Bridge Projects, 2025.
Harbourside’s Role
Working in a design-build setting for Dexter Construction, Harbourside Engineering provided the preliminary and detailed structural bridge and geotechnical design services for this project as well as the erection engineering. Harbourside also provided construction services during construction, including review of technical submittals, answering construction queries, and milestone site visits.
Highway 102 / 107 Preliminary Analysis
Harbourside completed a preliminary analysis that considered several design concepts for evaluation. Initially, project requirements dictated that fully integral abutments had to be used at each end of the tightly curved structure. Through experience and in-depth analysis, Harbourside clearly demonstrated to Dexter and NSPW that due to a combination of the tight horizontal radius of curvature, thermal movements, perched bedrock conditions and foundation skews that semi-integral abutments were technically preferred over fully integral abutments.
Girder Erection and Design
In addition to the structural design work, Harbourside was responsible for the erection design for the new curved steel trapezoidal box girders. Construction engineering services also fell under Harbourside’s purview, in the form of timber lagging walls to facilitate excavation for foundations. This excavation had to be completed without any impacts on the congested and busy road network within the influence zone of this project.
Girder erection was completed using a crane and stick build methodology, with girder segments being lifted in place during off-peak hours (nights and weekends), the aid of strategic lane drops, and an approved traffic phasing plan.
As a design-build project with an accelerated schedule, Harbourside was tasked with developing the preliminary bridge design during the in-market tender period. This was to enable Dexter Construction to complete their bid and construction plan. After award, Harbourside completed the detailed design in a packaged and accelerated manner to allow Dexter Construction to initiate construction activities on site as soon as practicable. Approved GA’s and foundation drawings were released six (6) weeks after award, followed by all of the girder details. This timeline allowed for the creation of shop drawings, ordering of materials and fabrication of the curved twin box girders in parallel with site construction. Finally, the remainder of the bridge design was completed well within the overall project schedule.
In addition, the project also included the short extension of an existing culvert at the adjacent Sucker Brook as well as an MSE headwall to mitigate environmental impacts associated with the widening of the culvert to accommodate upgrades to Highway 102 Northbound.
Near the end of the new bridge design, NSPW hired Dexter and Harbourside to complete 17 major highway overhead sign structures in the area of the new interchange. During this phase, Harbourside was responsible for the coordination with NSPW, Dexter and the overhead sign manufacturer. We completed the detailed layout and foundation design for each of the overhead signs, and conducted the geotechnical field investigation (test pits) and geotechnical design for these ancillary structures as well.
Unique Challenges
The use of fully integral abutments for this underpass structure set up abutment racking movements and embedded energies that led to large restraint forces in both the abutments and piers (transferred to the piers through the pot-type bearing assemblies). This embedded energy and restraint could theoretically be handled through design, but Harbourside identified that, when the pier bearings need to be replaced in the future, the embedded energy in the system at the time of replacement was a safety issue. Once the energy was released when the original bearings were removed, it would be practically impossible to force the structure back into the original restrained geometry. With semi-integral abutments and bearings properly orientated along the secant line to the point of fixity, the restraint forces were eliminated, thus reducing the design loads in the foundations and pier bearings and allowing for the future replacement of the pier bearings in a safe and practical manner.
Social Impact
Halifax, and the Halifax regional Municipality are home to some of the most congested roadways in the country. The additional connection points created by this overpass, and the improvements to Highway 102/107, will go a long way to improve transportation throughout HRM.
“The new extension of Highway 107 will create more efficient routes for people to travel and help reduce congestion and accidents that are currently seen on Magazine Hill….With our growing population, projects like this are also important to help support those who want to come and live in our great province.”
—Fred Tilley, Minister of Public Works.