Abstract:  To investigate the effects of loading frequency on the pore water pressure accumulation characteristics and liquefaction process of saturated sand, a series of undrained cyclic torsional shear tests were conducted on Fujian standard sand with different relative densities using a vertical–torsional coupled shear apparatus. The dynamic responses of saturated sand under various loading frequencies were systematically examined. On this basis, considering the limitations of existing pore pressure models, a segmented incremental pore pressure model incorporating the effect of loading frequency was developed. The main conclusions are as follows:(1) Loading frequency has a significant influence on the development of pore pressure ratio and shear strain accumulation in saturated sand. With increasing loading frequency, the accumulation rates of pore water pressure and shear strain decrease markedly, while the number of cycles required to reach initial liquefaction increases. (2) The pore pressure response exhibits frequency-dependent fluctuation characteristics. As the loading frequency increases, the fluctuation amplitude of pore water pressure decreases, and the evolution pattern of the pore pressure–cycle relationship changes, indicating that the pore pressure accumulation process is characterized by distinct stages.(3) Based on the stage-dependent variation of the incremental pore pressure ratio with the number of cycles, an existing incremental pore pressure model was modified to establish a segmented incremental pore pressure model that accounts for loading frequency effects. The model predictions show good agreement with the experimental results of this study and can reasonably capture the pore pressure accumulation behaviors reported in the literature for Nanjing fine sand and coral sand, demonstrating the applicability and potential extensibility of the proposed model under different sand types and loading conditions.