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Finding the right intermediate foundation systems technique

By Barb Feldman

We provide innovative foundation solutions for the worst soil conditions,” said Mark Tigchelaar, president and founder of GeoSolv Design/Build Inc. “The bulk of what we do is ground improvement with intermediate foundation systems to increase the stability and bearing capacity of a variety of soil types, including clay, sand, peat and fill, to provide sound footing on an engineered crust of soil where one is not naturally present.”

More than 10 employees work full-time at GeoSolv’s office in Vaughan, Ont., just northwest of Toronto, and the company’s clients are primarily in Ontario, although it has worked as far west as Alberta. GeoSolv’s projects have included tanks, wind towers, retaining walls, slopes and liquefaction mitigation, as well as a variety of other structural applications. Tigchelaar is a licensed engineer in both Ontario and Alberta; he is the past chair of the Canadian Geotechnical Society-Southern Ontario section and is a member of the Canadian Society for Civil Engineering, the Deep Foundations Institute, the Canadian Design-Build Institute and the Railway Association of Canada, as well as a number of local Ontario construction associations.

Since GeoSolv’s inception in 2006, the company has been the local design-build installer for the Geopier Foundation Company’s range of specialized patented intermediate foundation systems, many of which improve the ground in place and support loads through friction. The alternatives are often to dig out and replace bad soil or to put deep foundations down into the bedrock below and utilize a full structural slab, he says.

“For a slab on grade building – a commercial structure or a big industrial warehouse – the challenge with piles is that you must span across these hard points coming up to the surface, and that can structurally be quite expensive. One of the biggest advantages in utilizing ground improvement over deep foundations is the use of conventional construction using standard spread footings and unreinforced slabs.

“Seventy to 80 per cent of the jobs we do involve some sort of undocumented fill,” said Tigchelaar. “And might contain things that would be expensive to deal with if you had to dig it up and replace it with engineered soil. In the Greater Toronto Area, most sites with good hard soils near the surface have already been developed. The leftover pieces of land tend to have increasingly more and more problems. Furthermore, the rules for handling excess soils have tightened exponentially over the last 10 to 20 years, so much so that excess soils are almost considered a waste now unless you go through rigorous testing for various ‘contaminants’ to make sure it’s usable and safe.”

Rammed aggregate piers

The company recently installed over 6,000 displacement rammed aggregate piers (RAPs) on reclaimed land near the shore of Lake Ontario for a Toronto Transit Commission streetcar facility. The site had infill containing organics over organic silt and clay and zones of trapped peat over a glacial till and bedrock 35 to 40 feet deep.

“[This is] a fairly typical profile for the area – a hundred years ago, it was essentially all lake,” said Tigchelaar.

With the RAP impact system, a hollow mandrel and a hopper with a stone valve are pushed or vibrated into the ground to the desired pier depth, and then raised a pre-set distance while discharging stone – the valve allows the stone to flow through the mandrel when it is raised and closes to form a front to compact the stone when it is pushed down. The last two steps are repeated until the pier is complete.

“In the Geopier process, when you push out a cavity in the ground and ram stone laterally, you laterally stress and increase the capacity of the soil around the cavity. The undulated shape of the well-compacted rammed aggregate pier supports the load by friction by coupling the pier with the locked-in lateral stress of the surrounding soil,” he said, and can also completely eliminate or minimize spoils. Groups of RAPs with diameters ranging from 18 to 36 inches can be driven to depths of 10 to 60 feet or more, depending on a project’s requirements and soil conditions.

“In some cases, as with the TTC project, we added grout to the piers to help increase their internal shear strength through some very poor soil zones,” he said; grouted impact elements can be three to 10 times stiffer than RAP systems alone. The massive project took three crews only about five months to complete, he said, “and the structure is perform-ing as designed, verified through many load tests on site, including full-scale footing tests, and settlement monitoring following building construction.”

Finding the right technique

In addition to ground improvement techniques, GeoSolv’s various piling systems can offer distinct advantages for certain types of projects. One system relies on sections of rigid ductile iron pipe pile (DIPs) that are similar in strength but are much more corrosion-resistant than steel, says Tigchelaar.

“You can design DIPs like friction micropiles or like end-bearing pipe piles,” he said, to accommodate a range of ground conditions, such as on contaminated sites, where soils consist of loose sands or soft silts, or where groundwater is high.

“You take these five-metre sections of pile and fit them together with essentially a bell-and-spigot connection, drive them in with a relatively small breaker hammer, cut off the last pile section and use that as the starter section at your next pile location. So there’s almost zero waste for the over-all process,” which is quicker than having to weld sections of conventional tubular steel or H-pile, he added, and “you don’t have any issues of weakening at the welds, and installation vibrations are much lower than with a driven H-pile.”

Potential clients are offered free-of-charge feasibility stud-ies as well as obligation-free preliminary proposals, says Tigchelaar.

“We now offer about a dozen different technologies sourced from technology partners all over the world and we apply them to Canadian soils through a unique, peer-reviewed design-build process,” he said. “[But] if deep driven piles or dig-replace are the right answer, we’ll make sure to tell our clients that. If we don’t have a technique that’s right for the job, we’ll be the first to tell them. We try to help the client find the right solution that fits the problem – even if it’s somebody else’s.” 

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Piling Canada is the premier national voice for the Canadian deep foundation construction industry. Each issue is dedicated to providing readers with current and informative editorial, including project updates, company profiles, technological advancements, safety news, environmental information, HR advice, pertinent legal issues and more.