Pressão de pré-consolidação em função do tempo e da aplicação de pressões prévias

Abstract

Compaction is the main process of physical degradation of the soil. The process is defined as a reduction in the volume of partially saturated soil induced by anthropogenic causes that reduce the pore space by expelling air. In recent years, new techniques and methods, both in the laboratory and in the field, have contributed to a new focus on the evaluation of the structure of agricultural soils. The evaluation takes place based on the pre-consolidation pressure (σp), which is determined from the compression curve obtained by the uniaxial compression test. The present work had as objectives to determine which is the adequate time of application of the pressures during the test of uniaxial compression, aiming to improve the duration of these (article 1) and to verify if the application of previous pressures equal and greater than σp induce changes in mechanical resistance of the soil (article 2). Samples with preserved structure were collected in three soils, a Typical Dystrophic Tb Cambisol (CXbd), a Typical Dystrophic Red Yellow Latosol (LVAd) and a Typical Dystrophic Red-Yellow Argisol (PVAd), in horizons A and B. The samples were balanced in the matrix potentials of -10, -33, -100 and -1500 kPa. In the first article, the samples were used in the uniaxial compression test with pressure applications for one hour at each stage of the test. In the second article, the samples received previous pressures of 65%, 90% and 125% of the predicted σp before the uniaxial compression tests. The curve of deformation as a function of time adjusted appropriately to power models, indicating that there is arbitrariness in the definition of maximum deformation since the model is asymptotic. The application of pressures for more than four minutes does not seem reasonable to determine σp in partially saturated soils. The application of previous pressures at 65 % of the σp did not result in an increase in the mechanical resistance of the soil and the application of previous pressures equivalent to 125% of the σp caused an increase in the mechanical resistance of the soil for matrix potentials of -33, -100 and -1500 kPa.