Investigation into use of Bentonite Enriched Tailings for Earthfill Dam Core

Abstract

A 46 m high tailings and water retention dam at Bloom Lake iron ore mine site in northern Quebec is to be raised in three stages. The existing 18 m high first stage structure comprises a central till core confined between coarse tailings shell zones and slope protection layers of riprap and fine rockfill. Lack of sufficient quantities of suitable and economically viable till material for the future raises prompted an investigation into alternative design options for the dam core. Following a comparative options study, a Bentonite Enriched Tailings (BET) mixture of the abundantly available non-acid generating coarse tailings from the milling process and Wyoming sodium bentonite was identified as one of the options. The BET mixture would be suitable if it met the technical requirements of homogeneity and long-term permeability comparable to that of the till core in the existing dam and if it could be produced economically. Laboratory testing has been carried out to investigate the permeability and other geotechnical properties of the BET mixtures prepared using four grades/sources of bentonite and three local sources of water. The test results suggest the BET material to be a suitable alternative to the till fill. The paper presents the results of the laboratory investigation and the dam design concept using BET core. Field studies will be carried out to optimize material mixing and placement techniques.