Effect of Imperfect Direct Simple Shear Test Boundary Conditions on Monotonic and Cyclic Measurements

The direct simple shear (DSS) test is commonly used to assess shear strength of soil, estimate liquefaction resistance, or calibrate constitutive models. However, constitutive models are calibrated assuming ideal simple shear stress conditions even though this is not achieved in the DSS test. Near frictionless vertical boundaries cannot develop the complementary shear stresses necessary for ideal simple shear conditions. Difficulties in maintaining constant height during undrained tests violates the constant volume assumption. The top cap holding the top of the specimen can rock (rotate) during shear also violating the assumed perfect simple shear conditions. Parametric studies were conducted to investigate the effect of contact friction between the soil and vertical boundaries, vertical compliance and top cap rocking on the results of undrained DSS tests. The study simulates an industry-standard SGI type simple shear device using a 3-D finite element model and an advanced plasticity model to capture soil behaviour.M.A.S