Walking through the city, the average passerby will observe and admire the buildings around them, but more often than not, one of the most important yet under-appreciated components of these structures will be left unnoticed: their foundations. Buried underground and often forgotten, a building’s foundations anchor the structure into the ground and allow for it to rise securely above; without them our city would quite literally sink into the earth. And as anyone familiar with foundations can tell you, they are far from easy to design, and can often be very costly, given the unfavourable surprises one might find underground.
Foundations are also a part of the design process that UrbanToronto has never really gone in-depth on before, (sorry), but we are learning about them now from a GTA firm which has been working on tricky foundations for more than a decade. GeoSolv Design/Build Inc. specializes in ground improvement and foundation design in unstable soil conditions, and describe themselves as design-build geotechnical contractors that offer a range of services through all design and construction phases of a project. The company boasts twelve different technologies that can suit a wide variety of poor soil conditions, and provides solutions in soil stabilization, foundation design, and slope stabilization with applications in a variety of structures including building foundations, floor slabs, and retaining walls, among others.
Mark Tigchelaar, President of GeoSolv, explains that many of the projects in and around the GTA encounter unfavourable soil conditions that can threaten the budget and construction schedule of a project. Nearly 80% of work that GeoSolv takes on in the region involves what is known as undocumented fill, referring to land that was previously filled in with a random collection of soil, debris, and miscellaneous infill, often directly over topsoils. The majority of brownfield sites, industrial sites, and parking lots have these conditions, many of which are slated for redevelopment in today’s ongoing building spree. As Tigchelaar explains, there are ground improvement solutions available that can nearly triple the bearing capacity of the problematic soils, meaning smaller foundations are needed, thereby lowering overall costs on the project. By stabilizing the existing soils, one can avoid having to remove and replace the problem materials, allowing for ease of construction and time savings by preventing costly excavations.
Recently, GeoSolv completed work on the high-profile Mount Dennis Maintenance and Storage Facility (EMSF) at the western terminus of the Crosstown LRT, a project which involved the relocation of the historic Kodak building existing on the site. The bulk of the site soils consisted of silty sand, industrial fill, and native soils, while another portion of the site, where a smaller outbuilding was planned, consisted more of clay materials. These soils were unsuitable for typical spread footing and slab-on-grade foundations, and so remedial measures were required. Excavating and replacing the soils was considered, however, due to the industrial and deleterious nature of the fill, and the cost and logistics of trucking the soils off-site and replacing with engineered fill, the dig-replace option was too costly and impractical.
A system called Rapid Impact Compaction (RIC) was chosen for the majority of the building site where there were silty sand soils. The RIC system is a ground improvement technique that densifies shallow, loose, and granular soils up to six metres in depth while increasing the soil’s bearing capacity through the use of an excavator-mounted, hydraulic pile-driving hammer repeatedly striking a large circular shoe resting on the ground. The poor fill and loose soils were able to be improved in-place, rather than excavated and replaced. For the clay soils in the outbuilding, a Rammed Aggregate Pier system was chosen to provide the necessary bearing capacity to support spread footings and slab-on-grade foundations. Overall, the ground improvement approach on the EMSF saved considerable money and kept the project moving.
GeoSolv was recently employed on a project in Cambridge, Ontario, with their work on The Grand, Phase II condominium project. The 12-storey building had two levels of underground parking and was situated on the east bank of the Grand River atop loose sandy silt and silt soils. A deep foundation solution was considered, however, given installation difficulties, cost overruns, and schedule delays during installation of a similar system on Phase I of The Grand development, the owners were looking for a more cost-effective solution. The Geopier GeoConcrete Column (GCC) method was chosen, a technique which uses a controlled, ready-mix concrete to build fast expanded-base rigid inclusions with very high capacities. The GCC system provided a solid footing for the building, and allowed construction to proceed on schedule. The system also allowed for a high-capacity spread footing to be used, which offered cost and time savings over a deep foundation alternative.
Poor soil conditions can affect any construction project, from condo towers to low-rise residential, office, or retail buildings, infrastructure and transit lines, and more. Tigchelaar explained that GeoSolv has worked on a wide variety of building typologies and infrastructure projects, both as part of private-public partnerships or working directly with public or private stakeholders. Basically, issues with foundations and problem soils can strike any project, anywhere, but innovative, sustainable, and environmentally-friendly solutions are available to mitigate these issues. As Toronto and the GTA continue their rapid building boom, it is important to ensure that we are on solid ground for a stable and sustainable future ahead.
For more information on foundations in problematic soil conditions, or to find out more about GeoSolv and their work, you can check out their website, here.
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