Weathering effect on the small strains elastic properties of a residual soil

BOGADO, GUSTAVO O.; FRANCISCA, FRANCO M.; FRANCISCA, FRANCO M.; BOGADO, GUSTAVO O.

Geotechnical and Geological Engineering

Springer

Año: 2019 vol. 37 p. 4031 - 4041

0960-3182

Residual soils in the northeast Argentina,southeast Paraguay and central and southern Brazil are the result of the weathering of a near-surface basaltformation. To assess the effect of weathering on the small and large strain mechanical properties of residual soils and saprolite, disturbed and undisturbedspecimens from the city of Obera´ in Northern Argentina were collected and tested in the lab. Soil samples were tested from the surface down to 14 m indepth where a moderated weathered rock stratum was reached. Confined compression tests with complimentary shear wave velocity (S-wave) measurements wereperformed in all recovered samples. The degree of weathering of each specimen was evaluated by computing the weathering index (WI). The effect of degree of weathering, disturbance, effective stress,natural moisture content and saturation on soil stiffness was evaluated. The interpretation of theexperimental results indicates that the mechanical behavior of residual soils at high strain levels is mainly controlled by the degree of weathering, the initial void ratio and the effective stress. However, at low strain levels, these soils behave like cemented soils and the stiffness of the skeleton is mainly controlled by the presence of weak bonds between particles caused by the presence of oxides and sesquioxides, and matric suction. To characterize this behavior, a new relationship between WI, effective stress and S-wave velocityis proposed. This relationship can be used to estimate the degree of weathering of residual soils using S-wave velocity measurements.