Resonant column and torsional shear testing: A comprehensive study on measurement and analysis

The Resonant Column and Torsional Shear (RCTS) test is a widely used laboratory method for evaluating the dynamic properties of geomaterials, particularly shear modulus and damping ratio. This study presents a detailed assessment of the RCTS device, emphasising its calibration, measurement accuracy, and improvements in testing techniques. Various calibration methods, including proximitor calibration and equivalent radius correction, are examined to ensure precision in shear strain measurements across a wide range of strain amplitudes. In this study, the dynamic properties of intact gypsum plaster specimens were investigated under varying cyclic loading conditions using cyclic torsional shear tests. The results indicate that shear modulus decreases while damping ratio increases with increasing strain levels. Furthermore, the study highlights the significant influence of loading rate, which increases with rising loading frequency and torque amplitude under both sinusoidal and ramp waveforms. The findings establish a clear correlation between loading rate and dynamic properties, with higher loading rates leading to an increase in shear modulus and a reduction in damping ratio. These insights contribute to the improved standardization and reliability of RCTS testing, enhancing its applicability in geotechnical and earthquake engineering, particularly in soil-structure interaction and rock dynamics studies.