Mineralogical analysis of a residual soil from Medellín Dunite (Colombia) and its influence on physical properties and unsaturated undrained shear strength

Abstract

The residual soils have a physical-mechanical behavior that reflects their formation process. In the present work, a residual soil derived from Medellín Dunite was characterized mineralogically and its influence on the physical properties and unsaturated undrained shear strength was evaluated. The samples were taken in the area adjacent to “Canteras de Colombia”, in Bello municipality (Antioquia, Colombia), on the east side of the Medellín-Bogotá highway. To obtain a relationship between mineralogy and physical-mechanical properties, mineralogical characterization with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Mössbauer spectroscopy was done to determine the mineral phases present at three depths above 1.80 m in a soil profile derived from Medellín Dunite. The index properties and undrained shear strength of these soils were determined, the latter by the unconfined compressive strength (UCS) test and unconsolidated-undrained (UU) triaxial compression test. The residual soils of Medellín Dunite, have a particular mineralogical composition, which has a significant bearing on their physical-mechanical behavior. The more superficial soils (0.00 a 0.30 m) are richer in iron oxides and hydroxides (hematite, maghemite, and goethite) and aluminum hydroxides (gibbsite), forming bonds between the particles that produce soil aggregation. They are of lateritic behavior and fragile, and present, more significant cohesion and larger undrained shear strength than deeper soils (0.30 m to 1.80 m), these present lower content of oxides and oxi-hydroxides and higher content of silicates like clinochlore and tremolite.