Abstract

The aim of the study was to evaluate the impact of three states of compaction and two degrees of initial water saturation in direct shear parameters in two Hapludox. We studied a Hapludox-LVd (0.55 kg kg^-1 clay) and a Hapludox-LVdf (0.62 kg kg-1 de argila), in Brazil. We made a map of isolines of soil resistance to of the 0.07-0.12 m layer, which had a higher compaction state and, along with the soil density, we characterized three compaction states which were used as treatments. Statistical analysis consisted of comparing cohesion averages (C) and internal friction angle of the soil (f), in the three states of compaction, degrees of initial water saturation and depths. To analyze the behavior of C and f, depending on the initial density (Dsi) clay content (Arg) and the degree of initial water saturation (Gsi), we generated regressions involving the variables. The states of compaction did not promote significant changes in the values of C, but the depth of 0.07-0.12 m, which concentrated the largest deformation, showed values of C higher than the others. The f did not vary with the Dsi or soil moisture and proved to be the most affected by the clay content of the soil. The C increased with the reduction of Gsi and with increasing Dsi and was more influenced by than Dsi by Gsi, showing that the state compaction or history of tensions already experienced influenced by the soil has more strongly influenced the resistance to shear than the degree of water saturation.

Key words: Cohesion, internal friction angle, compressive behavior, no-tillage system.