The Gateway Program was established by the Province of British Columbia, as a means of addressing growing traffic congestion throughout Metro Vancouver. The Port Mann/Highway 1 (PMH1) Improvement Project is a component of the Gateway Program, the largest infrastructure transportation project in the history of British Columbia. In February 2009 the Province announced it would enter into a contract with the preferred component to design and build the new, 10-lane Port Mann Bridge and Highway 1 improvements.
This massive $2.4 billion infrastructure project was a five year design build contract with its primary objective of reducing travel time by up to 30%. In addition to the new Port Mann Bridge, the project required the widening of 37 kilometres of freeway from Vancouver to Langley which also included widening of seven Highway 1 overpasses, replacing nine Highway 1 interchanges, built or rebuilt of 15 new overpasses and underpasses at the Cape Horn interchange.
Reinforced Earth Company (RECo) was awarded the contract to design and supply the Mechanically Stabilized Earth wall for the project. Overall, RECo provided approximately 70 MSE walls that total over 37,000m2 of wall face area. RECo’s walls types included Abutment Walls and 2-stage retaining walls in heights up to 12m. RECo was involved in all three segments of the PMH1 project.
The East Segment is located east of the Port Mann Bridge; two additional lanes in each direction were built to 200 Street. A total of 17 walls were designed and supplied in this segment by RECo that included seven (7) bridges with a total of fifteen (15) perched abutment walls:
• 176th Street underpass, with 4 abutment MSE walls
• 160th Street underpass, with 2 abutment MSE walls
• 152nd Street underpass, with 2 abutment MSE walls
• 160th Street west bound ramp underpass, with 2 abutment MSE walls
• 112th Ave. pedestrian Underpass, with one abutment MSE wall
• 160th Street flyover west bound ramp, with 2 abutment MSE walls
• Barnston Drive underpass, with 2 abutment MSE walls
In addition to the bridge abutment walls, RECo designed and supplied eleven (11) other retaining walls with TerraClass system including off-ramps at the 156th Street intersection.
The Central Segment included the Cape Horn interchange which required extensive upgrade where RECo designed and supplied sixteen (16) MSE structures. Due to poor ground condition, the majority of construction was carried out on an improved ground. To help accommodate settlements, RECo designed ten (10) 2-stage walls, with about 7,000m2 facing area; as well as four (4) walls undertaking EPS blocks surcharge. The 2-stage wall consists of TerraTrel facing in the first stage and TerraClass facade in the second stage. The TerraTrel wall is a wire-mesh facing wall that can flex and can tolerate larger settlements as compared to the TerraClass system. The first stage is the TerraTrel wall which is also considered as a preloading. After the preloading stage is complete, the facade panels are installed and connected to TerraTrel facing utilizing connector rods and coil loops. The void between the two facings is filled with self-compacting gravel.
The West Segment is located west of the Central Segment. One additional general purpose lane was added in each direction resulting in widening and replacing of overpasses and interchanges. Reinforced Earth walls were used in widening and replacing of the following structures in the West Segment:
• BNSF Railway overpass, with 2 bridge abutments
• Boundary Road overpass, with 2 false abutments
• Cariboo Road underpass, with 2 bridge abutments
• Sprott Street underpass, South abutment
• Kensington Avenue underpass, South Abutment
• Gaglardi Way Intersection (2-stage walls)
• Government Street abutments, with 2 abutment walls and a wing wall
• Grandview ramps, 3 structures
• Brunette overpass, northeast retaining wall
One of the challenges in the PMH1 project was the performance based seismic design that was mandated by the Ministry of Transportation of British Columbia. The required seismic performance criteria for MSE walls were dependent on the return period of the design earthquake. The three performance criterial were 1) immediate functionality, 2) repairable damage and 3) no collapse after project design earthquakes with return periods of 475, 975 and 2475 years, respectively. A specialized geotechnical consultant was retained to carry out rigorous analyses based on response spectra and multiple time-histories. Naesgaard Geotechnical Ltd. performed a series of two dimensional numerical dynamic analyses using the program FLAC to assess the internal stability of Reinforced Earth walls in 5 defined cases. The internal design of the wall sections for these cases were designed by RECo utilizing a pseudo-static method and then modeled in FLAC to be analyzed for deformations under different seismic events. Numerical analyses indicated that the relative displacements within the Reinforced Earth structure were well below the allowable rupture strain and met the Design Build Agreement requirements.