Subsurface Condition Assessment, Syncrude Refinery Canada, AB

A mobile crane collapsed while lifting, which occurred due to an unknown and unseen underground void. No GPR scan was ordered by plant engineering and craning and rigging department. Outrigger positions were not scanned either to make sure that the ground beneath the concrete pad is solid and firm enough to withstand the dead weight of the crane. A load bearing capacity investigation would also be recommended on crane pad locations prior to crane placement.

Scan Area

Scan location was selected to check the perimeter of the collapsed void to find the actual lateral size of it. A GPR scan was carried out with a 350MHz Hyper Stacking System around the existing and collapsed void using safe work practices. Scan lines were collected every 16” to create a high-resolution radar image for the analysis and the report.

The image above is showing a typical sinkhole formation (see image above the radar cross section). The funnel shape (V-shape) of possible sinkhole formation is noticeable on the radar image.

Interpolated 3D GPR image rotated in plan view

After the last scan line was collected, a 3D radar image was created onsite to provide urgent information to the mitigation crew. Based on the radar imaging the outline of the unseen possible void was determined and marked on the surface.

Underground utilities were also located and marked on the radar image (see blue lines indicating underground pipelines).

The collapsed void was treated, and the danger was mitigated by a licensed geotechnical engineer.