Open-cut trenches should be consigned to the scrapheap of outdated construction methods whenever possible, just as open-heart surgery is, Ontario Regional Common Ground Alliance (ORCGA) members were told during a recent online workshop.
University of Waterloo civil engineering professor Mark Knight, the executive director of the Centre for Advancement of Trenchless Technologies at the university, said open cut should be minimized or banished, given that trenchless technology translates into less damage to existing infrastructure, fewer greenhouse gas emissions and less inconvenience to the community.
“Instead of doing open-heart surgery, what we’re going to do is, we’re going to do microsurgery, so we’re going to make a few excavations on either end, or go through access points such as manholes and fire hydrants, and be able to fix or rebuild the pipelines,” he explained.
Knight gave his presentation to ORCGA members several times during the month of March as the alliance opted for six half-days of Dig Safe workshops instead of its annual convention due to the pandemic.
Trenchless technology has advanced significantly during the past decade, Knight said, with less invasive techniques now frequently in use for a wide variety of jobs including utility line installation, replacement, rehab, inspection, location and leak detection. Typical jobs include work on water and wastewater systems, gas, petroleum and chemical pipelines, electrical and communications networks and access ways and other small-diameter tunnels.
“What we’re going to talk about are typically nonperson entry pipelines, that’s going to be around 900 or 1,000 millimetres or 36 to 42 inches in diameter,” said Knight. “A person can get in a 36-inch pipeline, however there’s not much room to be able to actually work. So there’s always a move between what is person-entry and not, anywhere between 36 to 40 inches or more.”
Two popular trenchless methods used for new installations are microtunnelling and horizontal directional drilling (HDD).
Microtunnelling is generally used for shorter distances with its boring machines operated by remote control. It starts with digging sending and receiving pits to the required depth, inserting a microtunnel boring machine into the sending pit, cutting a hole through the ground and pushing the new pipe into place.
“Right now there’s more microtunnelling projects going on in the Toronto metropolitan area than anywhere else in the North America,” said Knight. “So, a very successful tool in the toolbox.”
HDD is also increasingly common for installing new pipelines and the method can be used for much longer installs, over one kilometre, Knight said, including river crossings. It’s useful for installing small- to medium-diameter pipes and ducts and it’s used extensively by the gas, water, telecom and electricity industries.
“We’re using this technique that’s been well developed, and we have a very good contractor base in Canada to be able to offer this service across the country,” said Knight.
Asset management and inspections are also increasingly easy to undertake using trenchless technologies, Knight noted.
“To look at the condition of existing pipelines, we have a variety of different tools in our toolbox,” he said. “We have some very sophisticated TV cameras that can go in and scan the pipes. We can measure their outer roundness, we can look for cracks and fractures, infiltration inside these pipelines and do reports.
“And there’s well-established procedures in order to be able to classify the defects.”
Other techniques pioneered in Europe, such as building new pipe inside old using cured-in-place pipe liners with wet-to-dry pipe materials, have been in use for decades.
Knight also made cases for using trenchless technologies for their environmental, social and project cost savings. One photo from the presentation, taken recently by Knight, showed a main street in Wiarton, Ont. torn up by invasive open-cut trenches with extensive losses accruing to businesses.
The Government of British Columbia has formally recognized the environmental benefits of trenchless technologies and incorporated trenchless strategies as part of its approved carbon credits regime.
“They show at least a 75-per-cent reduction in carbon emissions,” said Knight, noting there is a carbon calculator that’s part of the province’s climate action toolkit.
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