Project Spotlight: Winskill Aquatic Centre, Delta

Overview
DIG completed a multi-phase investigation and design program for the new Winskill Aquatic Centre and related park works. The scope included drilling, CPT and SCPT data, MASW for seismic inputs, lab testing, liquefaction and settlement assessments, and foundation recommendations for a new pool complex with below-grade mechanical spaces.

Site and design drivers

The pool basins and mechanical areas are founded several metres below existing grade, so the foundation concept targeted very dense Vashon drift soils to control differential movement. The western at-grade portions required a different footing approach over near-surface Capilano sediments, and the building brace bays required tie-down anchors to resist uplift. A site-specific Vs30 from MASW established seismic design inputs for the structural team.

What we did

• Multi-phase subsurface program: Review of prior work at the site and nearby facilities, new auger holes and CPTs, SCPT shear-wave data, MASW testing, and targeted lab testing for consolidation and index properties. Findings confirmed a thin sequence of over-consolidated silt and clay over dense to very dense till-like sands and silts.
• Seismic characterization: MASW established an average shear-wave velocity, providing a site-specific Vs30 for code-based spectra and pool structure design.
• Pool and building foundations: Pool structures and below-grade areas are taken to the dense Vashon drift bearing level at the bottom of excavation, with gym and classroom areas detailed to suit the near-surface Capilano sediments. Tie-down anchors are included at brace bays to meet uplift.
• Excavation staging and protection: Temporary slopes and localized shotcrete facing were set to keep the excavation stable, with specific procedures for working near existing light poles, staged cutting, anchor installation at corners, and cover requirements to protect exposed faces until backfill.

Construction reviews

During excavation, we verified bearing at the design subgrade elevation, protected the prepared foundation subgrade from softening, and coordinated sequencing with the contractor and structural team so footings and pool slabs could be released promptly once conditions matched the report assumptions.  

Outcome

The site-specific seismic inputs, foundation approach on dense native soils, and clear excavation staging allowed the team to advance the pools and building foundations on schedule, while protecting adjacent infrastructure and maintaining safe, workable subgrades avoiding pile foundations to support near grade foundations.