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 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 major flood is possibly due to suffusion in the base soil of the piers. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Variations in excavation construction periods for fissured soil transportation engineering lead to differing unloading rates, which affect the soil's mechanical properties. This study utilizes a triaxial testing system to conduct monotonic and cyclic loading undrained shear tests on undisturbed fissured samples as well as remolded samples subjected to three distinct unloading rates. The K0 consolidated samples are regarded as soil mass that undergoes no unloading during testing. The findings indicated that the initial unloading rate influences the reloading shear mechanical properties of undisturbed and remolded specimens. The effects of unloading rates differ between undisturbed and remolded soil, a discrepancy attributed to inherent fissures. Specifically, undisturbed soil exhibits significant damage at low unloading rates due to fissures, while remolded soil experiences strength augmentation due to compaction with decreased unloading rates. Similarly, unloading will cause a loss of strength. Structural disparities result in the monotonic loading strength of undisturbed specimens being higher than that of remolded ones. In contrast, remolded specimens demonstrate greater dynamic strength under cyclic loading, likely because fissures deform, diminishing overall dynamic strength. Subsequent microscopic analysis, utilizing SEM images, along with a discussion of macroscopic inherent fissures, elucidated the impact of unloading rate on soil damage mechanisms, advancing the understanding of fissured soil behavior post- unloading. The study of mechanical properties of fissured soil following varying unloading rates is crucial for comprehending its damage mechanism and determining post-unloading soil strength parameters, providing valuable insights for practical applications in soil engineering.

The bearing and deformation characteristics of monopile foundation under the monotonic and cyclic loads are key factors to consider in the design of the transmission tower structure or offshore wind energy converters. The model tests and numerical simulations of monopile foundation under monotonic and cyclic horizontal loads were performed in sand to explore the bearing characteristics and the deformation characteristics of pile. The potentially affected factors including loading height, relative density of soil, displacement amplitude were analyzed. The results show that with the loading height varies from 1D to 4D, the horizontal static bearing capacity of the pile under different the soil relative density decreased by 1.63-1.9 times, and the peak bending moment increased by 22.9%-36.8%. Under the cyclic loads, the peak load on the pile top increased by 31.7%-56.1% for each 1 mm increase in displacement amplitude. The stiffness of soil around pile varies as the number of cycles increases with the development trend of decreases first and then increases gradually. As the horizontal load and cycle number increase, the range of the displacement of soil extends towards the bottom of pile, until it covers the entire lower part of the model.