Investigation of Dempster Highway Sinkholes: km 82 and Two Moose Lake

This report presents the results of a project that aims to understand and, if possible, recommend actions to remediate the issues caused by the formation of sinkholes at km 82 and km 102-103 of the Dempster Highway. At km 82, this has resulted in sudden collapse of the right-hand side driving surface of the highway. Major sinkholes have been repaired at this location on at least two occasions (June 2014 and Aug 2014) and the culvert at the site was replaced in October 2014. Undated photos suggest earlier sinkholes have formed at this location (SRK Consulting, 2014). Subsidence was also repaired in August 2015. At km 102-103, there has been general subsidence and sinkhole formation along the left-hand side of the road. Subsidence between km 102 and 103 has been regularly repaired as part of routine highway maintenance and is therefore not documented. At this site, Two-Moose Lake is now encroaching on the road embankment.