Hydrogeotechnical characterization of a metallurgical waste

Abstract

This paper presents the results of hydrogeotechnical characterization tests carried out on the metallurgical waste (MW) from a tailings impoundment located on the terraces of the Moa River, Cuba. Characterization of the MW includes chemical and mineralogical analysis, oedometer tests, triaxial tests, tensile strength tests, determination of the water retention curve, and shrinkage and permeability tests. The MW, which has a grain-size distribution similar to that of a silt, mainly contains iron and heavy metals minerals and has low plasticity. Consolidated undrained triaxial tests on remoulded samples indicate a dilative behaviour, with a decrease in pore-water pressure near failure. The material is susceptible to liquefaction when subjected to a cyclic load in the triaxial test. Hydraulic conductivity, soil stiffness, and compressive and tensile strength of the MW have an important dependence on the degree of saturation and vary significantly during the drying process. The results indicate that, during the drying process, cracks in the MW initiate in quasi-saturated conditions. The cracks increase the hydraulic conductivity by more than one order of magnitude compared with that of intact samples of MW. The main environmental risk with this MW is the possibility of liquefaction under a cyclic load due to an earthquake and the increase in saturated hydraulic conductivity due to desiccation cracks.Key words: desiccation cracks, hydrogeotechnical properties, liquefaction, metallurgical waste, characterization.