Solo siltoso da formação Guabirotuba reforçado com fibras de polipropileno

Abstract

Several studies have sought to improve the mechanical behavior of soils, with the use of synthetic or natural additives, for use in civil engineering works. In this context, research with the use of polypropylene fibers for soil reinforcement, shows an improvement in the behavior of the soil when subjected to tensile and compression .In this scope, considering the lack of research that study the effects of polypropylene fiber in soils that make up the Guabirotuba Formation, whose sediments lie mostly in the municipality of Curitiba (PR), the present research aims to evaluate the effects in the mechanical behavior of a silty soil belonging to this formation, when reinforced with the random addition of such fibers. Therefore, compaction tests were carried out on normal Proctor energy, unconfined compressive (qu) and to splitting tensile strength (qt), using fiber contents of 0%, 0.10%, 0.25%, 0.35% and 0.50% relative to the dry mass of the soil. The results showed that the aforementioned addition and respective increases in the polypropylene fiber content led to a decrease in the maximum dry density (ydmax), whereas there was little variation in the optimum soil moisture (wo). The behavior observed in the dry specific weight occurs because the fiber, a material with a specific density lower than that of the soil, starts to occupy spaces previously filled by the soil grains. Still, it was possible to verify that the optimum humidity varied slightly, since the fiber is hydrophobic and, therefore, does not absorb water. It was also observed that the values of (qu), (qt) and the secant stiffness module corresponding to stresses in 50% of qu and qt (E50) increased with the addition of fiber up to 0.25%, which was the one with the highest mechanical benefits, and therefore being defined as the optimum content. After this content, the values of these characteristics decreased to 0.35%, increasing again when the content was 0.50%. A possible explanation for this behavior is that as the amount of fiber increases in the mixture, the effect caused by the grains of the soil is lost because there is a decrease of grains in the specimen, which comes from the greater occupation by the fiber. Material that previously rubbed and bonded with the fiber is not enough to generate such interlocks and frictional force. After adding 0.35%, the polypropylene fibers assumed the role of the soil and stuck to each other, generating interlocks and friction between the fibers. The increase of qu for the optimum fiber content was 50% compared to the soil without fiber, while the tensile strength (qt) showed an increase of 138%. A direct average traction / compression ratio of 0.15 (i.e., qt = 0.15qu) was calculated, mainly influenced by the fiber-soil interaction as reported in the literature. Finally, from the results obtained through the tests carried out, possible applications of soil-fiber mixtures were recommended for use in engineering works.