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Scenic places, tight spaces

Ontario-based AVERTEX proves how an innovative trenchless application helped reduce the construction footprint where limited space and neighbourhood preservation were the predominant challenges

Scenic places, tight spaces

Imagine owning a million-dollar home in an affluent neighbourhood, situated along the Canadian shore of scenic Lake Ontario, where the only thing standing between you and an unobstructed view of a spectacular evening sunset is – of all things – a sewer pump station.

Such was the case for several somewhat unfortunate homeowners whose properties, located at the far end of Timber Lane in the wealthy community of Oakville, Ontario (pop. 183,000), face directly toward this aging sewer eyesore. But as of mid-May 2012 – the date AVERTEX Utility Solutions Inc., based in Orangeville, Ontario, completed work on a new gravity sewer project – the scenery has since changed. The once-affected residents with homes that hug the narrow, gently winding Timber Lane, are elated.

Gravity system chosen

Addressing the pump station and sewer situation along Oakville’s Timber Lane had been on the city’s list of infrastructure projects for many years. Then, somewhat by coincidence, at an event sponsored by AVERTEX for demonstrating the intricacies of the AXIS laser guided boring system, developed by Vermeer, Oakville city officials became intrigued, and felt the innovative trenchless approach could be the long-awaited answer to their dilemma.

The city had been leaning toward eliminating versus upgrading the pump station for several reasons. First, there was access. The narrow two-lane street, void of curbs and shoulders, would present access challenges for the machinery necessary to replace the station without inflicting considerable cosmetic damage to the well established landscape. Second, replacing the pump station with a gravity sewer would save the city money, and eliminate the irritating, continuous droning noise coming from the station. And finally, there was aesthetics. Residents had long been annoyed by the pump station’s unsightly and view-blocking presence.

“Over the years, the ongoing saga of the pump station had progressed to the point where the city had decided the best solution would be to install a gravity sewer,” says Jason Kottelenberg, contract manager with AVERTEX. “Not only was the pump station an obstruction, it was expensive to operate. From a cost perspective, a gravity sewer is much cheaper, despite the increase in upfront costs to install.

“The city weighed the options carefully, but in the end, realized spending a few extra dollars up front to eliminate the pump station and convert to a gravity system would save them dollars in the long run. And it goes without saying that the residents living along Timber Lane were very supportive.”

The AXIS system has the capability to install a wide range of materials at very precise grades.

The AXIS equation

Founded by Jack Kottelenberg and Andy Blokker in 2003, AVERTEX Utility Solutions has since realized exponential growth. Both founders had been proponents of horizontal directional drilling (HDD) since its introduction to the utility construction industry in the early 1990s, so the company grew quickly. Today, AVERTEX is a recognized leader in underground and trenchless technology, specializing in utility construction and network installation services, with precedence for projects involving HDD.

In the fall of 2009, AVERTEX became the first trenchless installation contractor in North America to purchase the AXIS system. Since then it has used the innovative pit-launched trenchless installation method for several jobs – primarily sewer applications – where on-grade accuracy was critical. The AXIS system has the capability to install a wide range of materials at very precise grades, while eliminating some of the difficult steps associated with other installation underground techniques.

Having considerable experience completing a number of gravity sewer jobs where on-grade precision was paramount, Kottelenberg felt confident recommending the AXIS system for the Oakville project. But the on-grade requirement alone wasn't the only consideration. Preserving the integrity of this posh, tree-lined setting – situated just on the pristine Lake Ontario shores – was actually Kottelenberg’s primary motivation; a factor that underscored the decision to employ the AXIS system.

“Open-cut was not an option,” Kottelenberg says. “Given the narrow streets, established trees, and expensive homes, limited access and maintaining the integrity of the neighbourhood – as much as possible – trenchless was the only option. It’s a tightly tree-lined area with century old oaks and mature maples. The strict, on-grade tolerance required for this sewer also tipped the scale heavily in favour of the AXIS system.”

Charting the course

The plan called for installing a 10-inch (25.4 cm) diameter LPVC gravity sewer at 0.6 percent grade. In mapping the installation route for the AXIS laser guided boring system, Kottelenberg plotted a series of six consecutive launch pits – ranging from 13 to 30 feet (4 to 9.1 m) deep – and from 130 to 393 feet (40 to 120 m) apart. Size and dimensions of launch pits varied depending on the depth required at each point.

Given the confined environment, AVERTEX was forced to utilize a compact pit design. Soil samples indicated a layer of shale beneath approximately 16 feet (4.9 m) of soil, so after reviewing the various options, Kottelenberg felt slide rail shoring would be the safest. Space limitations precluded use of an excavator with reach capable of extending to the depth required, forcing Kottelenberg’s crew to lower a mini excavator into the bottom of the pit, dig out the final 3 feet (1 m) or so, jackhammer through the shale, and load the spoil onto the bucket of the larger excavator for removal.

“The most difficult part of the project was excavating the pits,” Kottelenberg says. “Four of the six pits had to be dug down 26 to 30 feet (7.9 to 9.1 m). But the constraints of the project, the area was so tight we could only use about a 30-ton (27.2 tonne) excavator. It took a week just to dig a pit. But once those were completed, with the AXIS system lined up and ready for the shot, this was the simpler approach because shale is easy and consistent tolerance-wise. The nice part about the AXIS system is that once we were set up, we knew it would be accurate.”

Tree protection zone

In addition to the equipment size restrictions imposed on the AVERTEX crew as a result of the narrow work and access space limitations, the affluent Timber Lane neighbourhood is also a designated tree protection zone. Hence, any excavation or construction work occurring within the zone necessitates procurement of a tree protection zone encroachment permit. That mandate required AVERTEX to a hire qualified arborist for oversight, inspection and monitoring throughout the process. Roots exposed during excavation were first cleaned using a vacuum machine, then cut by the professional arborist. One passable lane of traffic was required at all times, to ensure residents had access to and egress from the community.

Once the first pit was completed and the various components of the AXIS system secured, it took about three days to complete a bore. Crews worked in advance of the boring activity of the AXIS system to ready the next bore, which in turn, served as the launch pit for the second bore, and so forth down the line.

“To go from one manhole to the next took about three to four days to complete,” Kottelenberg says. “That included drilling backreaming and installing the sewer pipe … keeping in mind that the AXIS system was boring through solid shale at a very precise grade. The system worked beautifully.”

The home stretch

Boring at approximately 16 feet (4.9 m) on the final bore – parallel to scenic Timber Lane – required implementing a mixed-faced bore as the ground conditions en route to the lakeshore began to transition from shale to clay. The change in soil conditions presented a bit of a challenge down the home stretch, but as Kottelenberg confirms, such bores are not out of the ordinary, and certainly nothing his crews haven’t encountered previously.

“Toward the end, we came out of the shale into the clay and the drill head started to dip down a little, because the clay was so soft,” he says. “We employed a couple of different techniques to fill in the hole and reshoot using another head. Ultimately, we got through and made the bore in fine shape – on line and on grade. Such situations occur from time to time, as no project is without a challenge or two. And the AXIS system performed beautifully. The one minor problem we did encounter was more the result of not having the right drill head for clay conditions; nothing related to the boring system.”

The 13.5-inch pilot bore, created using a tri-cone cutter designed specifically for drilling through shale up to approximately 22,000 psi (1516.8 bar), was upsized to 14 inches (35.6 cm) after completing just one backream to accommodate for the 13.75- inch (34.9 cm) OV gasket used to connect the individual 20-foot (6.1 m) segments of LPVC sewer pipe. In the end, the new gravity sewer line – spanning 1640 feet (500 m) in all – flowed like a charm. And residents of this posh lake-view community no longer have to contend with the noise and obstruction of the unsightly pump station.

“With respect to this project, if it wasn’t for the AXIS system, we wouldn’t have been able to complete the job,” Kottelenberg says. “Trenching was not an option. Just getting to the depth necessary along the confined route with million-dollar homes on each side never would have flown with the residents. It would also have been difficult using a traditional HDD approach, given the extremely precise grade of 0.6 percent. Ultimately, laser guided technology made the job feasible.”

The Vermeer AXIS guided boring system is a pit-launched trenchless installation method designed to achieve pinpoint, on-grade accuracy.

Company info

1210 Vermeer Road East
Pella, IA
US, 50219

Website:
vermeer.com

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