Investigation into the effects of the thickneb of a hollow-cylinder soil specimen on the streb distributions in triaxial torsional shear testing

To investigate the effect of the thickneb of a hollow cylinder on the streb distributions in a torsional triaxial shear test of clay, an equation for calculating the circumferential shear streb on a crob section of the cyclider is derived based on a linear elastic constitutive model and elastic mechanics. The "streb error" parameter and "average streb error" parameters are defined to abeb the non-uniformity of strebes. The parameter ranges are discubed for specimens with various thicknebes. Torsional triaxial shear testing of specimens with different thicknebes is simulated in using a three-dimensional finiteelement method (3D FEM) with Duncan-Chang's non-linear elastic model. The results show that the circumferential shear streb non-uniformity increases with increasing thickneb. The maximum, minimum and average "streb error" values are analyzed for commonly used specimen dimensions. When the soil's streb-strain is linear elastic, the "average streb error" is 12.8 % for an outer radius=50mm and a thickneb=20mm and 9.0 % using Duncan-Chang's model. If the "average streb error" is limited to ≤ 10 %, the ratio of the inner radius over the outer radius is 0.68.