A influência da sucção na deformabilidade de subleitos rodoviários: efeitos da variação de umidade, método de compactação e gênese dos solos

Abstract

This thesis presents a study on the influence of suction on the resilient and plastic characteristics of highway subgrade soils. The main focus was to evaluate the variation of suction as a function of postcompaction moisture variations, associated with seasonal fluctuations and the equilibrium moisture content of the subgrade. However, other conditioning factors, related to the initial compaction characteristics, were also evaluated. For this purpose, three soils from the state of Rio Grande do Sul were defined, with distinct geological and geotechnical characteristics. The experimental program consisted of physical, chemical, mineralogical, microstructural and hydromechanical characterization tests. Among the most relevant tests, it is mentioned the obtaining of the soil-water characteristic curves using the filter paper technique and the repeated load triaxial tests to obtain the resilient modulus and permanent deformation. To simulate the range of moisture changes in the field, postcompaction moisture content variations of -4%, -2% and + 2% were adopted, according to the equilibrium moisture content observed on the subgrades of Brazilian highways. In addition to postconstruction moisture variation, other variables of interest associated with the compaction process were evaluated: moisture, effort and compaction method. It was found that the compaction method does not impact in the soil microstructure and, therefore, does not influence the evaluated properties of interest (stiffness and soil infiltrability). With the increase in compaction effort, a better arrangement of the particles was noted, resulting in an increase in the resilient modulus and a greater water holding capacity by the materials. The variation in compaction moisture content also caused microstructural changes, influencing the infiltration capacity, expansion, stiffness and plastic behavior of the soils: the higher the initial moisture content, the lower infiltration rate, expansion and stiffness of the materials and the greater their permanent deformations. Regarding the effects of postcompaction moisture variation, it was found that with drying there was an increase in the stiffness of the soils, while with wetting there was a reduction in that stiffness and a greater accumulation of permanent deformations of these materials, showing the influence of the matric suction variation on the performance of the three soils studied. Suction, as a fundamental parameter for understanding the behavior of unsaturated soils, was related to all the properties of interest evaluated in this work, corroborating its relevance in the study of this type of material. In addition, it proved to be the best variable to represent the effects of moisture variation on the elastic and plastic behavior of soils subjected to cyclical loads. In view of this, models for predicting the resilient modulus and permanent deformation were proposed with the inclusion of this parameter. The models proved to be highly predictive, constituting important tools to be incorporated into the current mechanistic-empirical design methods. Furthermore, it was found that permanent deformation is not a major factor in the performance of the studied soils used as subgrade of conventional flexible pavements, because for stress levels acting on this layer, deformations were low and, in general, tended to the shakedown state.