The influence of amorphous silica on the aging of a remoulded loessial soil

A large number of soil formations in nature exhibit increments in stiffness and strength properties after deposition or even with aging after remoulding and compaction. Post-depositional diagenetic processes in the former case and various thyxotropic mechanisms in the latter case are usually postulated to explain the observed behaviour. Some horizons of the Argentinean loess formation show high shear strength properties in natural conditions and even with aging after remoulding, while others with similar origin and mostly identical physical-geotechnical parameters develop a sudden collapse as the soil is saturated. Samples of both types of loess were studied in this work to evaluate the reason for such behaviour. A battery of mechanical tests shows that the increments in strength and stiffness are time-dependent and that the values measured after 28 days of aging reach almost 70% of those corresponding to undisturbed specimens. Effective stress tests and suction control during aging confirm that the regain in strength is mostly due to a real cementation process and not to an increase in suction as is usually assumed. Mineralogical and chemical tests confirm the presence of amorphous silica which, in an alkaline environment as presented here, generates cementation reactions that bond the particles together and cause the development of a much stiffer structure.