Nova Scotia·CBC Investigates

Sinkhole investigation launched on Trans-Canada Highway near Oxford

Last month, a CBC News investigation showed indications that the Trans-Canada Highway near Oxford, N.S., was built over a sinkhole.

Last month, a CBC News investigation showed indications that the highway was built over a sinkhole

Crews drill the first of many boreholes that reach more than 30 metres underground near Oxford, N.S. The holes will allow for better analysis of the geology beneath the Trans-Canada Highway. (Brett Ruskin/CBC)

The Nova Scotia government has launched an investigation into possible sinkhole activity beneath the Trans-Canada Highway near the town of Oxford, a key transportation link between the province and the rest of Canada.

This comes two weeks after CBC News published its own investigation showing indications the highway was built over a sinkhole when it was constructed in the 1960s.

Crews arrived at the site Monday and began drilling boreholes next to the roadway using specialized equipment. They are retrieving sample cross-sections that will be analyzed to determine what layers are under the highway — dirt, gypsum, bedrock or water.

The holes will reach more than 30 metres beneath the surface, the depth of roughly two Peggys Cove lighthouses stacked one atop the other.

Nearly 10,000 vehicles use that section of highway near Oxford every day.

Samples are retrieved from deep underground alongside the highway. (Brett Ruskin/CBC)

Sinkhole concerns in the Oxford area emerged last year after one suddenly opened up in the Lions Club park in town. Recent geological testing has revealed extensive potential for further ground collapse around that hole.

Last month, CBC News revealed the results of a weeks-long investigation related to the nearby Trans-Canada Highway that used images spanning eight decades, obtained from the National Air Photo Library.

They were arranged to produce a multi-year timelapse showing what geologist believe is the sinkhole as it existed before the highway, and after the road's construction.

Detailed LIDAR images, which use lasers to map the surface of the landscape, also show a band of sinkholes over 100 metres wide stretching several kilometres from Oxford to the town of Springhill.

Aerial photographs of the Oxford area, with a focus (red circle) on what experts believe is a sinkhole that was eventually covered by the construction of the Trans-Canada Highway. (National Air Photo Library (images)/Brett Ruskin (animation))

Modern civil engineering techniques can build over sinkholes by creating small bridges. However, in the 1960s when the Trans-Canada Highway was routed past Oxford, the strategy was to simply fill the hole with rocks.

Hany El Naggar, a civil engineering expert and Dalhousie University professor, said the current situation could have "catastrophic" consequences, with failure happening in an instant and with no warning.

The drilling crew and geology expert hired by the province work on the first borehole of the roadside sinkhole investigation. (Brett Ruskin/CBC)

Department of Transportation spokesperson Marla MacInnis confirmed via email that a geotechnical investigation began this week "that will give us a clear understanding of the conditions at this site and how best to monitor and/or respond to the findings going forward."

It's expected that many boreholes will be drilled. One lane of the highway was closed early this week to accommodate the drilling crew.

While the investigation is seen as an important first step, experts like El Naggar say the highway needs to be fixed "yesterday" to prevent a possible collapse.

About the Author

Brett Ruskin

Reporter/Videojournalist

Brett Ruskin is a reporter and videojournalist covering everything from local breaking news to national issues. He's based in Halifax.

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