Open File Report 1985-07

Tour of the Highvale Open Pit Coal Mine June 2, 1985 CIM-CSPG Conference

Authors: Fenton, M.M., Langenberg, C.W., Jones, J.F., Trudell, M.R., Pawlowicz, J.G., Tapics, J.A., Nikols, D.J.

Executive Summary

The Highvale Mine is situated about 80 km west of the City of Edmonton (figure 1) near the south shore of Lake Wabamun. Access is westward from Edmonton on Highway 16, and southward via a provincial road just east of Lake Wabamun. The route is paved except for a gravelled portion through the Paul Band Indian Reserve. Geologic investigations were conducted in three areas: Pits 02, 03 and 04 (figure 2).

The Highvale Open Pit Coal Mine, which is owned by TransAlta Utilities Limited and operated by Manalta Coal Limited, was initially opened to supply thermal coal to the Sundance Generating station. Current production is from three pits and supplies both sundance and the nearby Keephills generating stations.

The bedrock overburden in many places in the Plains of western Canada has been thrust by Pleistocene glaciers (Moran et al, 1980. Fenton 1983a, and Fenton and Andriashek 1978). Regional surficial mapping of the Wabamun map sheet (Andriashek et al, 1979) revealed much of the bedrock in the Lake Isle-Wabamun-Saskatchewan River area had been glacially disturbed and deformed. The deformed bedrock material is weaker than the unformed bedrock. As a result, highwalls cut into this sediment have greater tendency to fail than those cut into undisturbed bedrock. Foreknowledge of the location, structure, dimensions and hydrology of these glacially thrust masses is of value in mine planning management.

Preliminary investigations at the Highvale Mine in 1983 (Fenton, 1983b and Fenton et al, 1983) had indicated that glacially thrust bedrock material was widespread and that the presence of this material was contributing to the highwall failure near the east end of Pit 03.

Many of the highwall failures in Pits 02, 03 and 04 are likely related to the glacially thrust bedrock material. The implications of highwall failure are serious since temporary benches excavated in the highwall serve as transportation corridors and a working foundation for overburden stripping equipment. In addition to the risks posed to men and equipment such failures also result in potentially sizable additional costs resulting from the re-handling of overburden materials, disruption of mining schedules and outright loss of potentially mineable coal.