The Shamrock Lake Concrete Culvert Rehabilitation project in northern Ontario faced a number of structural design challenges and required an alternative solution to bring the old structure back to life.
The cast-in-place concrete box culvert constructed in 1938 16 metres below Highway 11 and located 31.5 kilometres north of Nipigon, Ont. was failing and needed to be rehabilitated in order to maintain vehicular access on the stretch of highway above it.
The project was the subject of an Ontario Good Roads Association webinar held recently.
The owner for the project was Northwestern Region MTO, the engineer was Hatch and the contractor was Teranorth Construction.
Armtec’s Tunnel Liner Plate was selected for the rehabilitation. It is designed specifically for lining soft ground tunnels and relining existing conduits under highways and railroads.
“It is ideal for rehabilitating existing culverts because it can be constructed from the inside,” explained Heba Ahmed, director of business development with Armtec.
“It’s available in different thicknesses which is dictated depending on the load demands. The plate itself me can be easily carried.
“Each plate is corrugated, curved and punched and then bolted together to form the design geometry.”
Liner provided the best solution for the project
Other options were also considered but were found to be more costly, labour intensive or time consuming.
“We looked at the precast box which had constructability challenges as well as structural design challenges,” said Anjelica Kierans, a structural engineer with Hatch. “The replacement bridge, which also had the same constructability challenges and was more costly; tunnelling replacements, which are high risk and high complexity and not well suited to meet the hydraulic requirements; and liners, which is what we selected which minimized the overall construction complexity.”
Kierans said additional constraints included critical spawning habitat for Brook Trout within the culvert; unknown depth of concrete footings; it was located in the Nipigon Palisades Conservation Reserve; a narrow MTO right of way; and there’s a TC Energy Pipeline Prescribed Area located outside of the right of way.
After considering other solutions, the Tunnel Liner Plate was proposed, which allowed the contractor to install the bypass pipe and build the structure around it.
A polymer coating was selected to provide the 75-year service life as required by the Ministry of Transportation contract.
“Using this product introduced huge cost savings as there was no need for costly excavations of this deep embankment or demolishing of the existing structure,” Ahmed said.
“One of the most important aspects of this is that it is a true structural liner. It’s designed to handle all of the loads without relying on any strength contributions from the host structure.”
Many factors considered throughout rehabilitation
When a reline is considered for a culvert structure hydraulic capacity is often the top concern, Ahmed noted.
“We were really concerned with the flow rate discharged from the structure and aim to minimize any hydraulic losses due to the reduced size of the reline,” she said.
“For this reason, the horizontal elliptical shape was selected and that structure measures 3.7 metres in span by 2.3 metres in rise. It was designed to reline the existing concrete box culvert which maximized hydraulic capacity as it has a higher conveyance factor.”
The plates and required hardware arrived onsite in bundles.
“After the contractor sorted through the plates and stacked them into the order of installation, they proceeded to build an access road down the steep angle off the side of the structure and used Bobcats to drive these plates down to the culvert location,” said Ahmed. “At the site for installation the crew dug a pit and installed a pump on the up stream side to pump water, down a pipe coming on the side of the structure. Once the dewatering set up was complete the crew proceeded with plate assembly following our plate assembly guidelines.”
The project was completed in September 2019.
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