The Highline Metrotown comprises a 53-storey tower and attached 3-level townhome units, founded over a shared, 8-level underground parkade. Highline Metrotown has a total of 327 residential units, a 13-floor hotel and about 4,700 square feet of ground-oriented retail space. Following project completion, Highline will be the tallest tower on Beresford Street, Burnaby, BC.

The excavation for the underground parkade measured up to 100 feet in depth and was advanced adjacent to hundreds of municipal utilities in addition to an 8-storey residential tower which was constructed concurrently.

At the design development phase of the project, Horizon directed a subsurface investigation comprising auger and odex drilling, dynamic cone penetration test (DCPT) soundings, and falling head permeability tests.

Based on the results of the subsurface investigation, a tied back shotcrete shoring system, measuring up to 100 feet in height, was designed to support the temporary excavation slope cuts. At the owner’s request, Horizon developed an optimized shoring design comprising of shortened tied back anchors. The optimized anchor length was derived from wedge analyses and estimation of weathered till thickness. The reduction in anchor lengths along the excavation shoring faces resulted in an estimated $500,000 in labour and material cost savings.

Since the west face of the excavation is located adjacent to an 8 storey building which was being constructed concurrently, Horizon provided an excavation shoring design which coupled as underpinning to support the future, abutting building surcharge loads.

Inclinometers were installed at the shoring walls to monitor for deformations during construction. The maximum shoring face deflection measured with the inclinometers was up to 48mm, prompting Horizon to provide supplemental shoring anchor tensioning recommendations, which were ultimately effective in stabilizing the shoring.

Following excavation shoring construction, large volumes of water were observed to flow from the east face of the excavation. Horizon reported this discharge to the City of Burnaby, which upon further investigation, was determined to have been caused by a municipal watermain pipe burst distant to the excavation (with water conveyed to the shoring via utility trenches). During and following the pipe burst, the excavation shoring drainage performed per design, and successfully mitigated build-up of hydraulic pressures behind the shoring face.

During construction, a large BC Hydro duct bank was encountered at a depth of about 7 feet along the south side of the excavation. In order to eliminate conflict between the duct bank and the proposed tie back shoring anchors, Horizon redesigned the south shoring face to comprise a cantilevered pipe pile wall.

Horizon Engineering is proud to be a part of the design build team that brought this geotechnically complex and world class development to fruition. Horizon’s collaboration with the project team resulted in innovative geotechnical design solutions which allowed the project to be completed on schedule and with significant costs savings resulting from optimization of the excavation shoring design.