Mapping an underground tunnel from 1891

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“Mom, what are those lines for on the ground? Those are social distancing lines son.”

In current times, when you see markings like the ones in the picture below on the sidewalk,  your first reaction is to stay 2 metres apart, but not this time.

Mapping an old disused underground tunnel:

GeoScan was tasked with mapping an underground tunnel that was constructed back in 1891 in downtown Victoria, BC.

This tunnel was protruding out from the building and underneath the sidewalk. As you could imagine over the past 100 years or so, the elements took its toll on the overall structural integrity.

GPR Tunnel

This resulted in the sidewalk above to start sinking.

Using Ground Penetrating Radar (GPR), GeoScan was able to map out the tunnel boundary (above ground) and the surrounding subusrface utilities in an effort to help the client with the renovation project and to prevent the sidewalk above from caving in.

The image below is raw GPR data from the site, displaying located subsurface utilities as well as the underground tunnel.