Abstract Dam B1 was approximately 85 m high and 700 m long along the crown when it suddenly failed in 25th of January, after 41 years of operations and deposition of tailings at the Paraopeba mining complex (Côrrego de Feijão), in Minas Gerais, Brazil. More than 250 people died and vast economic, social and environmental damages resulted from the collapse. Given the need to geotechnically characterise the tailings within the dam for a credible computational model of the failure, an extensive sampling and laboratory testing campaign took place. The geotechnical laboratory of the Civil Engineering Department at the Faculty of Engineering of the University of Porto (Portugal) was invited by CIMNE, under a contract with VALE, with MPF agreement, to conduct this program. This paper will present a description of the sampling campaigns in the remaining post-mortem dam/reservoir tailings were the failure instability mechanics developed and the experimental program undertaken to test the tailings in advanced laboratory tests. The results that embrace evaluations of the physical, hydraulic and mechanical properties, deduced from integral samples selectively collected and prepared as described, which allowed to define the geotechnical parameters necessary for the referred analyses are here resumed.

Abstract According to previously available research and seismic microzonation studies a large area of the Guayaquil (Ecuador, South America) sits on estuarine deltaic deposits which consist of weak and highly compressible clays with diatoms. The nature of these fine-grained deposits may determine difficulties in a proper estimation of the soil properties. In this respect, the paper provides a detailed geotechnical and geophysical characterization of these soft clays, carried out in the estuarine complex of the Ecuadorean city. Borehole logs, standard penetration tests (SPT), piezocone tests (CPTu), a seismic dilatometer test (SDMT), a non-invasive geophysical survey, and laboratory tests were performed and then compared to analyze the static and dynamic geotechnical parameters of these deposits. The interpretation of the results highlighted the higher reliability of CPTu and SDMT rather than SPT and characterization lab testing to estimate soil shear strength, compressibility and stress history due to the soft nature of these clays, underlining also a certain sensitivity to the presence of the diatoms.