Deep Burial Simulator nears completion

Posted on October 22, 2015

Researchers to explore how erosion affects subteranean pipe systems

Prof Ian Moore

THE NEXT STEP: “We haven’t previously been able to test how earth loads – deep burial – affects joints or the impact of soil erosion on buried pipes,” says Queen’s Civil Engineering Professor, Ian Moore. “We’ll be able to study both of these issues in the new simulator”

In the wee hours of May 12, 2006, 16-year-old Skye Whitman was driving toward her Sudbury home after a late shift at work. Things were clearing up after heavy rains earlier that night but as she steered her car along Bay Street to where it crosses Fairbanks Creek, the ground dropped away from beneath her tires. The car plunged headlong into a gaping trench that cut across the road. It spun after hitting the solid wall of earth opposite. The wreckage bounced violently, landing back on the roadway. It was a terrible crash and Whitman was killed.

The culprit, it turned out, was a corrugated, galvanized steel culvert buried under the road. It had over the years, rusted, leaked, and buckled. As the water level in the creek rose and fell, as many thousands of trucks and cars rumbled over it, its strength slowly ebbed away. The rains that day were finally too much and the culvert collapsed, dragging the soil column and road surface down with it, leaving the dark, watery gash that killed Whitman.

It’s easy to take buried pipes for granted – it’s hard not to – but when they fail, the results can be disastrous. More often they are just very costly. Sewer pipes that leak or collapse can cause environmental damage and unnecessarily high water-treatment costs to cities. Water distribution pipes that leak or break can compromise drinking water supplies. Culverts can age before their time or simply reach the end of their service lives, requiring costly replacement and causing traffic disruption. Sometimes buried pipe can be repaired in situ but that’s expensive, too and it raises questions about preferred repair methods.

So, how do you design and build buried pipe systems that are durable, long-lasting and cost effective? When pipes fail, how can they best be repaired and made safe without tearing up the ground or breaking the bank? One of the best ways these questions are asked and answered is by experimentation at the GeoEngineering Laboratory at Queen’s.

I’m interested in fundamental engineering behaviour as a scholar but almost all of my work is directed toward solving practical problems,” says Queen’s Civil Engineering Professor Ian Moore.

Moore, along with colleague Richard Brachman, oversee the lab on West Campus. Together they’ve raised most of the money that’s gone into building, maintaining and staffing the facility. In it there are pits where researchers can bury pipe samples under various fill materials. Hydraulic actuators are used to apply loads at ground level to simulate tucks or heavy equipment parked overhead. Steel pipe can be tested under conditions of accelerated electrolytic corrosion. Polyethylene pipe can be tested under various heating conditions to examine long term behaviour over short periods. Joints between pipe sections can be tested for strength and integrity.

“The idea is to undertake field-scale construction in a controlled laboratory environment where we can know reasonably precisely what the soil conditions are, which we don’t always know in the field,” says Moore. “We can take our time, so we’re not under the gun with contractors, and at the end of the exercise we can load the systems up to collapse…. The work that we’ve done on all these different culverts is what defines many of the current international practices for these structures.”

It’s work that sets various design codes: the contemporary professional standards for the design and installation of subterranean pipe systems that guide engineers and builders in their proper use. When a company develops new pipe system components or repair methods, Moore and his team can also be hired to test the true qualities of the new products.

Burial simulator at Coastal Lab Queen's

ESTABLISHING CODE: Many contributions to the culverts section of the American Association of Highway and Transportation Officials (AASHTO) Bridge Design standard is based on buried pipe research conducted in these burial simulators at Queen’s University.

Unlike culverts, which are typically buried under only a few meters of fill, many sewer and water lines – gravity-fed pipe systems – need to be buried tens of metres deep to work properly relative to the surrounding topography. In those cases, loads on the pipe are more a product of the weight of the soil column rather than trucks and equipment passing overhead. The different conditions call for a different test rig. There is already a deep burial simulator at the lab but it can only accommodate pipes up to 60 cm in diameter and under specific fill conditions. To take research to the next level, Moore and his team needed something much larger and more sophisticated.

Now, thanks to a grant earned from the Canada Foundation for Innovation (CFI), that something is under construction. A 4.5-metre deep pit has already been dug and the way cleared for an addition to the lab building for the new deep burial simulator. It will be much larger and deeper than anything available now. Huge hydraulic actuators will apply loads to large, stiff steel plates, pressing down from ground level to simulate forces applied by tens of meters of soil. Not only that, but water can be pumped in and out of the pipe samples and surrounding fill to determine the effects of erosion around deeply buried pipes and the joints between them.

“What’s the impact of an erosion void on a pipe after it’s repaired?” wonders Moore. “There are lots of fundamental questions nobody has the answer to. We’re already in a unique position internationally and we’re going to be extending our capabilities with this new investment from the province and from the federal government so we can remain ahead of the people who are trying to reproduce what we have.”

Research gathered in the new deep burial simulator will help engineers design water and sewer systems to last longer and leak less. It will inform new ways to maintain and repair pipes reliably and safely without having to dig through thousands of tonnes of earth to do so. It will save municipalities and provinces – and their international analogues – untold millions so those agencies can continue to provide people safe and reliable access to sanitary and drinking water systems for years to come.

Professor Ian Moore and his GeoEngineering Laboratory from Queen's Engineering.