Void Backfill Design for a Steeply Dipping Coal-mine Void Below a Highway in Canmore, Alberta

Four coal seams were mined in the No. 1 coal mine on Canmore Creek, Canmore, Alberta using room-and-pillar-mining methods from the mid-1880s to the mid-1890s. Coal mining was conducted along seams inclined between 45° and 80° from horizontal. Highway 742 – Spray Lakes Road was constructed on top of the No. 1 mine. The depth from highway surface to the coal-mine void is less than 4 m below the highway surface.

Alberta Transportation (AT) is responsible for providing a safe, innovative, and sustainable provincial transportation system in Alberta. AT implemented the geohazard-risk-management program (GRMP) to identify, investigate, instrument, monitor, and, if required, repair geohazard sites. The portion of Highway 742 underlain by the No. 1 mine is referred to as the S012 site. The steeply inclined coal-mine voids in Canmore present a special case in that the potential for brittle collapse of the highway surface is exacerbated beyond what would be expected for flat-lying coal-mine voids.

AT commissioned a series of investigations of the coal-mine void beneath Hwy 742 caused by mining of the No. 2 and No. 3 seams at the No. 1 mine. The results of that work, and a conceptual design of mitigation measures for addressing the coal-mine voids at the S012 site are described in this paper.

Grapel, C., C. Mulhall, H. Hong, B. Rogers, N. Parry, and R. Skirrow. 2018. “Void Backfill Design for a Steeply Dipping Coal-mine Void Below a Highway in Canmore, Alberta,” in Geohazards 7: 7th Canadian Geohazards Conference, June 3-6, 2018, Canmore, AB. Paper #122. Canadian Geotechnical Society (CGS)

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