Effect of loading frequency on the stiffening and decline characteristics of shear modulus of saturated coral sand

To investigate the effect of loading frequency f on the stiffening and decline characteristics of dynamic shear modulus of saturated coral sand, a series of multi-stage and single-stage stress-controlled undrained cyclic shear tests were performed on medium dense saturated specimens under isotropically consolidated condition in various f (0․ 01 Hz, 0․ 05 Hz, 0․ 1 Hz, 0․ 5 Hz, and 1 Hz) ․ The excess pore water pressure threshold shear strain(below which there is no excess pore pressure buildup) and the modulus threshold shear strain(below there is no shear modulus decline) of the coral sand were basically the same and they could be uniformly termed as the threshold shear strain γth, whose value is not influenced by f․ For γa≤γth(low strain level), the dynamic shear modulus G increases with the cyclic shear strain amplitude γa, and can be expressed as a quadratic polynomial function of the applied cyclic stress ratio CSR․ The maximum value of modulus stiffening index δs can reach 1․ 2․ For γa > γth (high strain level), the shape of G-γa curves is independent of f, the modulus decline index δd decreases in a negative power function form as γa increases; meanwhile, the decline rate of G with the number of cycles N decreases as f increases, and frequency-dependent δd can be expressed as an explicit function of N. © 2024 Chinese Society of Civil Engineering. All rights reserved.