Paste backfill of shallow mine workings for land reclamation in Canmore, Alberta

The coal mining history in Canmore, Alberta was presented along with reclamation activities that mine regulators carried out following closure of the mines after nearly 100 years of underground mining. The 7 seams that were mined commercially extend over distances of a few hundred feet and have been displaced by faults. Voids and collapsed rubble in shallow underground workings pose a risk of potential ground subsidence that can affect the stability of surface structures and infrastructure, including the planned development of the proposed Three Sisters Mountain Village on land above the abandoned mines. The village includes plans for 10,000 residential homes, 2 golf courses, and a resource centre. A mine works mitigation program involved drilling primary injection boreholes on a 15 m grid pattern to map the constraint zones in order to gain a better perspective of the subsidence issues as well as the effects of subsidence on structural stress and public safety. When determining mitigation criteria, various land uses and ranges of subsidence hazards were considered to be compatible with each land use. A paste backfill composed of aggregate from a locally available till overburden site was mixed with cement and injected into the void spaces. This paper described the cemented paste backfill injection method; confirmatory methods; maximum volume and pressure criteria; survey for ground uplift; and borehole camera and manual checks for cemented paste backfill in adjacent boreholes. Quality control testing was carried out by means of slump tests. It was concluded that cemented paste backfill mix could be used successfully to stabilize abandoned mine workings for land recovery. 8 refs., 5 tabs., 7 figs