Summary

The experience of the first twelve years of mining operations at Knob Lake, Quebec, has shown that severe ground-water problems exist in the mining area. These conditions are a result of a high water-table, active recharge rates and high permeability values of the geological formations, which in turn have enhanced the instability of artificial slopes. In order to account for these factors in obtaining optimum mine-design criteria, a detailed geotechnical programme combining hydrological, geohydrological, geochemical and soil mechanics investigations with the standard development programme of economic property evaluation is proving to be an efficient framework within which to conduct these investigations. More specifically, the hydrological programme is focused on water-balance studies for selected ground-water basins, while the geohydrology studies encompass water-table and pore-pressure measurements and the construction of flow nets for both ground-water basins and local areas (ore zones). The geochemical programme, now in its initial stages, is being invoked to define ground-water flow by utilizing certain minor and trace elements as natural ground-water tags. Chemical equilibrium of the major elements dissolved in the ground-water, with the minerals in the aquifers and aquicludes, may assist in defining ground-water flow domains or boundary conditions and residence times, in distinguishing between steady and non-steady states and, finally, in proportioning water-well discharges. The soil mechanics investigations are centred on obtaining shear-strength data, studying the distribution of discontinuities and defining slip geometries. An outline of some of these studies and case studies of some slope features are presented.

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