Variation of Elastic Stiffness of Saturated Sand Under Cyclic Torsional Shear

For soil elements surrounding the foundations of offshore wind turbines or oil platforms, very many loading cycles of varying amplitudes and frequencies are quite common. The influence of such cyclic loadings on the soil stiffness is a critical concern in the evaluation of the long-term performance of the foundation-structure system during its service life. Current understanding of this influence is however inadequate due to the scarcity of experimental data. This study investigates the variation of small-strain shear modulus (G₀) of saturated Toyoura sand subjected to cyclic torsional shear stress cycles with a small amplitude by using a RC/TS apparatus. Sand specimens of different densities have been tested. It is found that the G₀ value tends to decrease with loading cycles and the decrease is mainly associated with the initial loading cycles. When the number of cycles is beyond around 3500, the G₀ value tends to become stable. The degree of reduction of G₀ is not sensitive to the density of sand specimen and is generally within 10% for the range of densities investigated.