Quantification of uncertainty in direct shear test

Direct shear is one of the simple tests that can be conducted in the laboratory to obtain the shear strength parameters (i.e., cohesion and friction angle). Basically, all the values obtained from the laboratory tests must contain the uncertainties, due to some unknowns that come from the measure equipment (denoted as Type-B uncertainty, that can be quantified from the calibration of equipment) and random sources in the procedure of the tests (denoted as Type-A uncertainty). This study tries to identify the sources of uncertainties that contribute to shear stress parameters as a result from direct shear test, and quantifies the random uncertainties involved in the test (Type-A uncertainty). The method is by conducting some series of tests repeatedly and perform statistical analyses on the results. The direct shear test procedure is based on the standard of SNI 3420:2016 and the sample material being used in this study is typically sandy soil. Shear strength parameters are interpreted from the test by using a formula that was derived in the previous study from the shear strength equation which involves the values of shear stress and normal stress measured from the test. The result of repeated tests shows that the Type A uncertainty still produce a wide range of uncertainty for the shear strength parameters.