Creekside Crossing – Costco, Mississauga, Ontario
Ground reinforcement using Geopier Ground Improvement® Systems is a sound approach for undocumented fill sites across North America. In fact, since introducing precision ground improvement methods such as Geopier to Ontario in 2006, 70% or more of GeoSolv’s completed projects contain fill soil.
Since 1985, Costco has been rapidly expanding its presence in Canada and those frequenting it will note its popularity at the checkout and free in-store sample lineups. A natural location of expansion for them was in eastern Mississauga, which is about halfway between two of its busiest locations (Etobicoke and Heartland).
The Creekside Crossing location was perfect for Costco’s expansion interests, but only if their aggressive store opening schedule could be met. Costco would be a perfect fit in the Walmart anchored AAA retail development if it were not for the serious soil issues to be later addressed.
Costco construction typically features large, heavily loaded slabs on grade and light to moderate footings for their warehouse-style retail outlets. These developments are often completed with very aggressive schedules, with an opening target date that must be achieved.
The soils on the selected site largely consisted of up to 4.5 metres (~15 ft.) of very loose to compact mixed undocumented fill underlain by till. The groundwater level at the project site was generally consistent with the level of the adjacent stream at a depth of about 4.5m below the existing grade. The floodplain of the river (controlled by TRCA) had to be respected through the right grading and buffer zones. This resulted in a general grade raise over much of the building’s footprint.
The team required a cost-effective foundation solution that could be installed with minimal delays to the project schedule. Based on the undocumented nature of the fill soils, the geotechnical engineer provided an option of total excavation and replacement – an excessively costly item. More importantly, removal posed a significant schedule risk to the project due to the aggressive schedule imposed by Costco’s target opening date.
Ultimately, through in-depth discussions with GeoSolv, Fieldgate Construction Management Ltd. selected the Geopier GP3 system for its cost-effectiveness, speed of installation and ability to provide high capacity standard footing construction. The improved bearing capacity provided for standard spread footings by the GP3 System was 290 kPa at Serviceability Limit States (SLS) 425 kPa at Ultimate Limit States (ULS), significantly higher than the proposed engineered fill approach. The GP3 system also provided for an unreinforced slab on grade, verified through Finite Element Analysis by GeoSolv, in coordination with the Project Structural Engineer.
Installation of the Geopier elements was done rapidly from existing grade and full-time quality control was provided by GeoSolv’s construction team. The GP3 element capacity was verified in the field by a full-scale load test which demonstrated less than 10 mm of deflection at the maximum design load. Golder Associates provided quality assurance inspection for Fieldgate and was involved in the design and foundation system selection process.
“The Rammed Aggregate Pier System by GeoSolv proved to be reliable and met a tight timeline which contributed to the overall success of the project and the happiness of the client.” – Jeff Tolton, Golder Associates
Construction of the Costco was completed in 2013 (meeting the target date) thanks in part to the rapid installation and schedule surety provided by GeoSolv’s innovative ground reinforcement solution at the early stages of the project.
Additional information on the Geopier GeoConcrete System can be found here