Compressibility and small strain stiffness characteristics of silt-hematite mixtures

Abstract

Iron mining waste is disposed of near mines and forms iron ore (hematite) tailings dams. Furthermore, the distinctive characteristics of hematite particles can affect the geotechnical properties of soil. This study aimed to experimentally examine the compressibility and small-strain stiffness of silt-hematite mixtures. Silt-hematite mixtures were prepared in an oedometer cell at a fixed relative density with different hematite contents (0% to 100% in weight). Vertical displacements and loads were measured with the oedometer, and shear and compression waves were measured using bender and piezo-disk elements, respectively. The results showed that the void ratio and compressibility increased, while the constrained modulus decreased with increasing hematite content as hematite formed porous aggregate owing to high van der Waals forces. The elastic wave velocities (Vs and Vp) and small-strain moduli (Gmax and Mmax) increased with increasing hematite content owing to hematite's high stiffness and coordination number. Furthermore, the elastic wave velocities of high hematite-content specimens were practically constant at low-stress levels (<20 kPa), because of the van der Waals forces being greater than the skeletal forces. This study suggests that the geotechnical properties of hematite-containing soils, hematite-coated soils, and iron ore tailings soils can be evaluated by the hematite ratio.