At a glance
Mixed-use tower with three levels of parking immediately beside the East Hastings viaduct. Our scope covered shoring and permanent underpinning at the bridge abutment, contaminated-site ESC design/monitoring, hydrogeotechnical seepage analysis and dewatering planning, permitting, and a bridge protection program accepted by the City.
Abutment foundation loads sat directly beside and above the future parkade walls, creating a major surcharge that a conventional basement wall could not safely absorb—especially under the City’s very tight movement tolerances at the viaduct. Our solution: isolate those loads with a permanent, anchored underpinning wall installed top-down ahead of excavation, designed for at-rest conditions and the bridge surcharge.
Working with the environmental consultant, we developed an erosion and sediment control (ESC) plan tailored to the site’s contaminated context, including protected catch basins, lined stockpiles, on-site sedimentation/treatment, wheel-wash protocols, and frequency-based monitoring. Discharge was routed to the sanitary system under a City permit with flow limits for 2- and 5-year storms; the plan also sets holding capacities and compliance with City bylaw and bulletin requirements.
Along Glen Drive we faced difficult excavation conditions: dense utilities, strict street surcharge limits, and no allowance for long-term encroachments. We used a mix of cantilever pipe-piles, tieback anchors, and deadman blocks with walers to control deflection while staying clear of ducts and vaults. Where anchors risked utility conflicts, we required exposure and casing to prevent drift. Street-side staging was governed by explicit setback/surcharge rules, and the ESC system was moved to the east side of Glen Drive to avoid loading the shoring.
We installed piezometers during site investigation and measured permeability of the granular/till units to inform seepage modeling and temporary dewatering. The data show perched water above low-permeability tills/bedrock; this supported a sump-based approach sized to seasonal conditions and aligned with our ESC treatment/permit pathway. We also prepared and submitted the water-use permit application for construction dewatering on behalf of the client.
Ultra-tight movement thresholds. Our monitoring plan set the first/green threshold at 5 mm vertical and 5 mm horizontal on the abutment; amber at 5–8 mm; and a red “stop-work” threshold that, if reached, would trigger the pre-approved bridge-closure detour plan with traffic control on standby. Because the closure trigger sat so close to the green/amber bands, we tailored the underpinning design, staged excavation, and anchor testing (sacrificial performance tests and proof/performance testing of every permanent tieback) to keep movements essentially zero.
Our viaduct monitoring plan defined green/amber/red movement thresholds, stop-work/restart procedures, reporting cadence, and communications. Field instruments included survey prisms, crack gauges, tilt sensors, and scheduled walk-throughs. A traffic control bridge-closure detour was pre-planned and accepted by the City to protect the public if red criteria were ever reached. Post-construction provisions keep limited monitoring in place.
With thresholds this tight, recorded movement was only ~1 mm, well within the green band—considerably stricter than typical industry shoring tolerances—demonstrating that the permanent underpinning, sequencing, and testing strategy effectively protected the viaduct while advancing the excavation.
By combining permanent underpinning, street-side shoring tailored to utilities and surcharges, and permit-aligned ESC/dewatering, we advanced excavation and structure while keeping the viaduct and public realm within movement and environmental limits.
