Synchronicity and Asynchrony of Particles Loss Intensity With Unsteady Seepage Loadings in Suffusion

Suffusion is a crucial mechanism to trigger seepage failure in hydraulic structures. The unsteady seepage, particularly in internally unstable gap‐graded soils, poses significant risks. However, the impact of unsteady loading has been scarcely explored in quantification, leading to temporally indistinct response of the finer particles loss. Here, we use a rigorously calibrated numerical model to clarify the unsteady seepage, encompassing step‐rise loading, flood loading, and random fluctuations, to forecast suffusion process in gap‐graded specimens. The results indicate as the seepage loading varies, the intensity of finer particles loss can manifest either synchronicity or asynchrony, characterized by alterations in sufficiency and locations of the finer particles sources. In the initial phase of increasing unsteady loading, when finer particles sources are sufficient and particles loss is primarily concentrated in surface layers, the suffusion intensity exhibits synchronicity with the loading pattern. As suffusion progresses upstream and interconnected seepage develops throughout the specimen, the middle layers subsequently become the primary source of particles loss. During this period, the insufficient source constrained the finer particles carrying capacity of the powerful seepage loading, resulting in the asynchrony. Through discussion, the critical hydraulic gradient emerges as a pivotal variable in suffusion model, rendering the prediction of synchronicity and asynchrony challenging. In addition, the cumulative hydraulic gradient is introduced to comprehensively encapsulate the power of unsteady loadings in both magnitude and duration. The results bring implications to actual suffusion that the synchronicity and asynchrony between suffusion intensity and seepage loading need to be taken seriously in practical applications.