Caracterización de suelos residuales a partir de ensayos in situ en el sur de la provincia de Loja

Abstract

Residual soils exhibit distinctive mechanical properties derived from the weathering and alteration processes that originate them. This genesis produces a marked anisotropy in their geotechnical behavior, limiting the direct application of empirical correlations developed for transported soils. In the present study, in-situ tests are used to geotechnically characterize these soils and to estimate their ultimate bearing capacity. The analysis is based on the compilation and interpretation of SPT and CPTu test results, performed on a cohesive residual soil transitioning to saprolite and affected by hydrothermal alteration and weathering processes. Based on the obtained data, geotechnical units were defined and iso-surfaces were delineated to identify zones with similar geotechnical behavior. Likewise, correlations were established between in-situ test results, strength and deformability parameters determined in the laboratory, and the estimated ultimate bearing capacity. The study area is located in the central-western sector of the city of Cariamanga, Calvas canton (Loja Province), on residual soils developed from volcanic and volcanoclastic rocks belonging to the Ahuaca Unit (MAh). These rocks, affected by hydrothermal processes, constitute the bedrock of the residual soils analyzed, whose composition, degree of alteration and degree of weathering govern their geotechnical behavior. By developing a two-dimensional geotechnical model with a southeast–northwest orientation, the materials were zoned into five geotechnical units (A, A’, B, C, and D), which reflect representative ranges of the obtained geotechnical parameters. Units A and B account for approximately 72% of the spatial distribution, while units A’, C, and D comprise the remaining 28%. In general, the defined units correspond to fine-grained residual soils with moderate geotechnical conditions, with Unit C standing out for its higher bearing capacity and undrained shear strength. IV By adjusting the geotechnical behavior of each geotechnical unit with a typical rock-to-soil weathering profile according to Pope (2013), this study identified the association and presence of two weathering levels: Saprolite and Pedolith. The geotechnical units A and B are associated with the development of pedolithic soil, whereas units A’, C, and D are associated with the development of saprolitic soil, evidencing the variability in geotechnical properties as a function of the prevailing degree of weathering. Keywords: Residual soils, SPT test, CPTu test, geotechnical parameters, empirical correlations, 2D geotechnical model, weathering profiles, ultimate bearing capacity