Geotechnical Evaluation of a Ghanaian Black Cotton Soil for use as Clay Liner in Tailings Dam Construction

Abstract

The purpose of tailings impoundment is to contain tailings produced from mineral processing. Chemicals used in mineral ex-traction processes are usually hazardous to biota and fauna and their presence in tailings may pollute the environment. To pre-vent the flow of such contaminants from tailing dams into the environment, low permeability membranes or seals are used in the basin of the tailings dam as barrier layer. Geomembranes and natural clay liners are typical examples. The use of naturally occurring clay materials provides the most economical liner for tailings dam construction. Lateritic clay and weathered shale have been evaluated for use as liner. Black cotton soils occur in substantial quantities in parts of Ghana but their potential use as a clay liner has not been evaluated. This study presents laboratory evaluation of a typical black cotton soil from the Accra plains of Ghana as potential clay liner for tailings dam construction. Results of the study indicate that the hydraulic conductiv-ity or permeability, plasticity index, fines content and cation exchange capacity of the black cotton soils met the specification of typical clay liner systems. The soil however failed the specific gravity and liquid limit requirements marginally and hence, the soils may be used as clay lining system in tailings dams.