A Rational Interpretation of Laboratory Direct Shear Test Results for Soils

An important property of soils is the shear strength, which guarantees the stability of geotechnical structures. This property is represented by two parameters: internal friction angle and cohesion, obtained from shear testing in the field and laboratory. The direct shear test is the most popular and intensively used for determining shear strength parameters. The aim of this paper is to present a rational procedure to interpret the results of the laboratory direct shear test for defining the strength parameters of soils. Two series of direct shear tests under consolidated and drained conditions (ASTM D3080) were carried out with samples of a wet well-graded sand (SW) compacted to a dense state, from Cutimbo’s bank of aggregates, and saturated soft clay (CL and CH), from lacustrine deposits of Puno city. The procedure was applied to the results, for two soils, and the strength parameters were determined considering typical response curves and validity ranges of normal stresses for application purposes. Calculated strength parameters values were consistent with reported values in several publications and reduces the uncertainty of the reported values from direct shear tests.