Effects of internal erosion on mechanical properties of different soil compositions and its impact on their cyclic response

Suffusion, a process whereby water gradually carries away fine particles from soil, is thought to be one of the possible reasons for the settlement or inclination of bridge piers after a major flood (delayed displacement). The aim of this study is to offer fresh insights into suffusion and its mechanical impact on the affected soil, with a specific focus on how it relates to bridge pier failures. Riverbed material is replicated with relatively larger fine particles than those used in past studies which focused on soil in embankments or dikes.

Through both monotonic and cyclic loading tests on soil samples with varying initial fines contents, while maintaining a constant relative density of 79%, several important discoveries are made. The small strain stiffness of suffused soil fluctuates as erosion occurs, along with a decrease in shear strength and an increase in soil contraction under monotonic stress. Furthermore, the research simulates the train loading exerted on the base soil of bridge piers susceptible to suffusion by subjecting the soil samples to cyclic loading both before and after erosion, mirroring practical conditions. The key findings of this study reveal that the stiffness of soil drops during erosion with no significant deformation of the soil. This leads to a large strain accumulation in the soil specimens under subsequent cyclic traffic loading. These findings highlight that the delayed settlement or inclination of bridge piers under cyclic or train loading after a major flood is possibly due to suffusion in the base soil of the piers.