Análise da anisotropia de areias reforçadas com fibras naturais e sintéticas

Abstract

During the execution of earthworks, suitable soil deposits with the required strength and compressibility characteristics are not always available, making it necessary to search for soils in more distant locations or to adopt stabilization methods that adjust their properties to meet the needs of the project. The use of fiber-reinforced soils in Civil Engineering has shown promising results in the construction of embankments, dams, and earth structures. However, despite the research already carried out on this topic, there is a lack of focus on the anisotropy generated during the field compaction process, which produces a sub-horizontal alignment of the fibers. In light of this, this work presents and analyzes results from laboratory tests performed on composites made with two different sands (river sand and dune sand) and two types of fibers (coconut and polypropylene) in which the failure plane forms different orientations with the preferential orientation of the fibers, as in the case of triaxial compression and extension tests and direct shear tests. Results from previous studies carried out at GEOAMB supported this research and were used alongside data produced by the author. In the triaxial extension tests, the predominant effect of low confining stresses was observed, which, when associated with the use of the Mohr-Coulomb model (which assumes material isotropy), resulted in artificially high strength parameters, contrary to the expectations of reduced strength due to the unfavorable fiber orientation relative to the failure plane. Regarding volumetric deformation, polypropylene fibers proved more effective than coconut fibers in reducing dilatancy in the river and dune sand matrices in both triaxial compression and direct shear tests. In the triaxial extension tests, however, the use of both fibers led to a trend of increased volumetric expansion, although this trend was less pronounced for the polypropylene fibers. River sand, which has sub-angular particle shapes and a better grain size distribution than dune sand, showed more pronounced dilative behavior in the cases analyzed. Graphs relating cohesive gain to the angle between fiber orientation and the failure plane indicate that coconut fibers induce less anisotropy compared to polypropylene. Finally, computed tomography image tests and visual observations of fiber predisposition in failed samples confirm their tendency toward sub-horizontal alignment after sample compaction. Furthermore, it was noted that although both fibers tend to sub-horizontalize (supporting the hypothesis that the compaction process induces a preferential fiber orientation in the composite that directly affects its mechanical performance), coconut fibers tend to disperse and mix better in the sand matrix, while polypropylene fibers tend to agglomerate in some regions, which helps explain the less anisotropic behavior found in composites reinforced with coconut fiber.