Childcare Facility Built Above Stormwater System

Low Impact Development

Background Information and Challenge

During the construction of the Mount Dennis Child Care Facility, Toronto’s largest and first net-zero childcare facility, the contractor faced significant challenges due to available space for staging and construction sequencing. They needed to operate a crane with outriggers during the building construction. The only space available onsite was directly above the below-ground stormwater system, which needed to be installed in the early stages of construction. A solution was required to protect the stormwater tanks and reduce the ground pressure exerted by the outrigger over the tanks.


The below-ground stormwater infiltration system used was a Brentwood Stormtank® 25 series. Its heavy-duty infiltration gallery was installed within the parking lot to collect surface water runoff and infiltrate stormwater to match pre-development conditions. This was a low-profile 600mm tank rated for HS25 wheel loading. The point load of the outrigger was a cause for concern, and to mitigate the potential risk of damage to the system or the reduction of service life, the contractor reached out to Layfield for a solution to reduce vertical pressure above the Stormtank from the crane outriggers. Presto Geosystems provided a multilayer GEOWEB® system designed with Atra Keys & Clips to create a safe working pad beneath the outrigger. It is an advanced soil stabilization technology that confines infill material and controls the shearing and lateral and vertical movement of infill material. The Geoweb system’s effect is immediate and works on the principle of hoop strength. Its designed cross-section included a layer of Mirafi® RS280I high-efficiency woven geotextile layer below two layers of GW30V6 150mm cellular confinement GEOWEB®, infilled with 20mm crushed granular and topped off with a crane outrigger pad.


The Mirafi® RS280i provided reinforcement, delineation and separation between the pad layer, while the GEOWEB® provided confinement of the 20mm crushed aggregate compacted fill material. This concept reduced vertical pressure from the crane outrigger to within the HS25 loading limit of the storm tank system. Installation of the system was efficient and took approximately one day to complete. The contractor was delighted with the ease of use and installation to address this challenge and comfort, knowing the below-ground storage tank was protected.



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