Geotechnical case study of fine-grained transition soils in landslides: anomalous behavior in San Cayetano Formation (Loja, Ecuador)

Numerous landslides, either natural or produced by excavations in road works, occur in the intramontane Neogene Loja basin (southern Ecuadorian Andes) and can be associated with the clayey silts, low plasticity soils (ML). Thirty-two undisturbed samples from eight sites were tested in laboratory to characterize the stress-strain geotechnical soil response, showing a higher internal friction angle and higher cohesion with respect to the standard ML soil values. A testing profile of a road constructed with these soils has been modelled using finite element methods to calculate both the safety factor and the mechanism of evolution. Anomalous behaviour is evidenced when a standard ML soil type is considered in the model, with a higher security factor than the less stable and more susceptible ML soils of Loja basin. Therefore, this contribution may serve as a warning to designers and engineers when constructing new structures on these soils. Additionally, it enables the identification of the most effective test for assessing high susceptibility in ML soils, contributing to the refinement and enhancement of methodological procedures during project execution.