Determinação e análise dos parâmetros de resistência ao cisalhamento de um solo residual de basalto do campus Erechim - RS em condições naturais e inundadas

Abstract

This work presents results of the characterization analysis and the shear strength parameters of a naturally structured basaltic soil from the Alto Uruguai. For that, undisturbed and deformed samples were obtained from an area from a recent section on the campus of the Federal University of Southern Frontier (Erechim - RS). In summary, in the in situ conditions the following average values were obtained: natural moisture content - 43%; voids index - 1.72; porosity - 63%; degree of saturation - 71.95%; apparent specific natural weight - 15.15 kN / m³; density - 2.89; specific mass of the soil grains - 28.9 KN / m³. For the Atterberg Limits: LL - 71%; LP-56%; IP-15%; inactive (IA - 0.19), hard (CI - 1.87). In the unified classification (SUCS), the soil is MH - silt soil of high compressibility and medium plasticity. The granulometric analysis reveals: clay - 79.02%; silte - 11.17%; fine sand - 8.95%; average sand - 0.51%; coarse sand - 0.26% and fine gravel - 0.09%, silty clay. For the road classification the soil is framed as A - 7 - 5, clay soil. During the shear, it is observed that under natural conditions the soil changes from a ductile state to a state of peak resistance, this fact did not occur for the flooded condition. For both conditions, there was a common section, with a maximum value, where there is overlap of the stress versus strain curves. Note that for the natural condition there is a point of deformation, in common where the curves of shear stresses become constant, which was not identified for the flooded. During shear test, contractions occur. It is still verified that in the natural conditions reductions of the moisture content, due to the expulsion of the water from the voids. However, a decrease of this reduction occurs with the increase of the normal tension of consolidation, an attempt to explain this fact, would be that with the increase of the consolidation tension, there was the imprisonment of interstitial water in the voids, in contrast to expulsion. However, in the flooded conditions there was an increase in the moisture content during the rupture, this phenomenon occurred, seems to be within the predicted, because with lower tensions occurs increase of moisture content, caused by the smaller confinement. However, this increase decreases with the increase of the normal consolidation stresses. The shear strength parameters were determined through the direct shear test, from specimens extracted from an undisturbed soil sample in a natural and flooded moisture condition. In relation to the direct shear test, the values of the obtained parameters were of 29.5 KPa for the cohesion and 22.15 ° for the angle of friction, in the natural condition and for the flooded condition, the values of 17.5 KPa for cohesion and 18.26 ° for the internal friction angle. The shear strength parameters, under natural conditions, have higher values than under flooded conditions. It is believed that this differentiation in the value of the resistance occurred due to the reduction of the apparent cohesion during the flood. The tests proposed for the research were performed satisfactorily in the laboratory.