Resistência ao cisalhamento da areia do Porto do Açu

Abstract

A campaign of direct shear tests was carried out in the sands of Porto do Açu in order to know the behavior of this material in relation to shear strength, permeability and compressibility. Direct shear tests were performed on dry samples molded into four relative density: very loose, loose, medium and dense. For each of these domains, tests were carried out at four different nominal normal stress values (), 50 kPa, 150 kPa, 300 kPa and 500 kPa. The tests allowed a vast analysis of the characteristics of the / x h and h x v curves, verifying the variations in these curves motivated by changes in Dr and , knowing the influence of these factors on the peak resistance (') and on the magnitude and direction of vertical displacement of the top cap at failure (vf), in the occurrence of contraction or expansion of the specimen during failure. The angle of friction at constant volume (cv) was determined, according to the theoretical model proposed by Taylor (1948), and improved by Atkinson and Bransby (1978), obtaining for the sands of Porto do Açu, a value varying between 24° and 26°. From the study of variations in the vertical displacement of the top cap, a curve that relates the critical void ratio and the critical nominal normal stress was determined, being analogous to the critical state line proposed by Lee and Seed (1967). This curve indicates a division in the dilating or contracting behavior of the Porto do Açu Sands at failure, establishing whether a given sample, at a given void ratio, when sheared under a certain normal stress, will undergo dilation or contraction at failure. The oedometric modulus (Eoed) was between 6 MPa and 226 MPa (normal stresses between 12.5 kPa and 1600 kPa) and the permeability coefficient (k) varied between 1.9x10-3 cm/s and 1.2x10-3 cm/s (soft and dense specimens).