Transient shear response of saturated sands under frequency-controlled cyclic loading

This paper presents a systematic experimental investigation into the undrained response of saturated Fujian sand and calcareous sand under various loading frequencies. Based on dilatancy and contraction characteristics, the cyclic shear process is divided into three distinct periods: the shearing contractive period, the initial shearing dilative period, and the late shearing dilative period. Special emphasis is placed on the shear strain and pore pressure behavior of saturated sand under transient dynamic shear stress during each period, with analysis focused on their interrelationships and time-dependent evolution. The results demonstrate that loading frequency exerts minimal influence on the stress-strain behavior of saturated sand during the shearing contractive period. However, once the sample enters the initial shearing dilative period, loading frequency begins to play a more influential role in dilatancy response. This effect becomes most pronounced in the late shearing dilative period. Under low-frequency loading, significant dilatancy and deformation accumulation are promoted, thereby elevating the risk of deformation-induced instability. In contrast, high-frequency loading suppresses deformation accumulation, with the associated liquefaction risk primarily linked to strength instability.