Efeito do espaçamento entre reforços no comportamento de protótipos de muros de solos finos reforçados com geossintéticos

Abstract

Among the different types of retaining walls used to gain area through structured embankments, Geosynthetic-Reinforced Soil Structures stand out, due to their high productivity, flexibility, resilience, attractive costs and architectural possibilities. Although these structures are constantly evolving, some aspects of their design are little explored, such as the relationship between the deformability of these structures when designed with reduced vertical spacing, more precisely in projects using cohesive fine soils and geogrids. To demonstrate that smaller vertical spacings result in more homogeneous structures, with a lower level of load acting in the connection of the reinforcements with the face, enabling the construction of retaining walls with smaller displacements, even with embankments composed of fine and cohesive soils, the instrumented construction of 2 full-scale prototypes, with 2 m in height, was carried out with embankment formed by fine soil, with cohesion of 33.2 kPa at optimum humidity, instrumented with tell-tales, and face displacement meters. The two prototypes were designed with the same sum of final reinforcement strength, with Wall 01 built with 6 geogrids of 20 kN/m, spaced every 30 cm, and Wall 2 with 3 geogrids of 40 kN/m spaced every 60 cm. The structures were subjected to overloads of 20 to 120 kPa, and later had their massif flooded by an artificial rain system, in order to reduce the apparent cohesion and evaluate the mechanical response of the structure in such condition. In the central region of the prototypes, with 120 cm in height, the structures showed face displacements towards the embankment, with Wall 01, presenting values 55% lower than Wall 02, and at the top of the structures, where the walls suffered displacements outside the reinforced zone, Wall 01 presented face displacements 33% smaller than Wall 02, demonstrating the greater efficiency of the system with a greater number of geogrids. The wetting of the structures promoted the external displacement of the faces out of the reinforced soil body in all elevations, being more preponderant at the top of the structure. The reinforcements of Wall 01 showed maximum deformations on a strip that crossed the entire massif, similar to the Rankine rupture surface, and Wall 02 presented maximum deformations in the region of its face, indicating a higher level of stress in this area, considered critical for structures in reinforced soil. The comparison between the stresses mobilized in the reinforcements and the method of calculation of rupture proposed in the work, converged only in the analysis of the dry phase of Wall 01, while in the other conditions the mobilized stresses were much lower than those estimated by the calculation method. After overload of 120 kPa, the tensile strength of the central geogrid of Wall 02 presented mobilized stress values close to those determined by the proposed calculation method, however, the other geogrids of both Walls presented dispersed values. The displacement prediction method of GRS resulted in values exactly equal to those obtained by the instrumentation of the Walls. The results showed that under normal humidity conditions, for the same sum of resistances, the use of smaller vertical spacings between reinforcements was able to promote a reduction in face displacements, and consequently enable the construction of more rigid and homogeneous structures.