Eletroquímica coloidal e sua relação com a sensibilidade de um solo argiloso na foz do rio Amazonas

Abstract

Clays have always played an important role in the history of civilizations, mainly because they are a mineral resource with varied technological applications. Among the several existing types, sensitive clays (quick clays), for example, are very complex soft soils that are considered real challenges for engineers due to the difficulty in obtaining their geotechnical parameters. In this sense, the aim of the present study was to analyze the sensitivity of a clay soil found in a region of the city of Santana, in the state of Amapá, Brazil. To this end, physical and chemical tests were carried out, including the SPT (Standard Penetration Test), X-Ray Diffraction (XRD), Zeta Potential (ζ), pH, Cation Exchange Capacity (CEC), as well as resistance assays (Vane Test and Fall Cone Test – FCT). The analyzed area is located in the Macapá Fluvio-marine Plain, which is composed of sediments that were deposited both by rivers and by the sea as a result of the region’s proximity to the mouth of the Amazon River. The geological profile obtained through geotechnical investigation indicated that the soil is constituted of mottled sandy-clay sediments, sandy-silty sediments with plant remains, and sandy- silty sediments with pebbles. As for the mineralogy of the samples, they were essentially composed of quartz and three clay minerals: kaolinite, mica/illite, and chlorite. Regarding sensitivity, all samples were classified as quick clays, with medium or high amounts of organic matter (O.M.); greater organic matter content was associated with increased sensitivity. In addition, it was understood that the intensity of clay sensitivity was higher with the increase in monovalent cations and the decrease in divalent cations such as Ca2+ and Mg2+, which must have been removed by the O.M. The soil pH reading ranged from high to very high acidity, an expected classification due to the increase in H+ concentration due to the O.M. All samples showed similar ζ values, with the lowest being 31.3 mV and 33.2 mV, which are still considered high, indicating that the soil colloids repel each other, forming a dispersed structure. Our results were consistent with similar reports in the literature; however, regionalized studies are necessary for a better understanding of the local peculiarities capable of influencing the profile of this soil.