Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Civil and Environmental Engineering | en_US |
| dc.contributor.advisor | Yin, Zhen-yu (CEE) | en_US |
| dc.creator | Song, Shunxiang | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14588 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Investigating internal erosion in gap-graded granular soils under various shear loading conditions with CFD-DEM | en_US |
| dcterms.abstract | Internal erosion is one of the primary causes of catastrophic failures in geotechnical structures such as embankments, dams, levees, and offshore foundations. Traditional internal erosion studies have typically been conducted under highly simplified loading conditions, which fail to capture the complex hydro-mechanical interactions present in real engineering environments. This thesis addresses this gap by employing a Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) framework to systematically investigate internal erosion in gap-graded granular soils under various shear loading conditions, including hollow cylinder torsional shear, biaxial shear, direct shear, and ring shear conditions. These loading conditions are strategically chosen to represent key engineering scenarios, ranging from seismic-induced stress rotation to long-term stability of tailings dams. | en_US |
| dcterms.abstract | The thesis focuses on how the initial stress state and loading mode influence internal erosion and how the loss of fine particles due to erosion changes the mechanical behaviors of the post-eroded specimens during subsequent shearing. The results reveal that fines mass loss intensifies as the mobilized shear stress approaches the peak strength. This behavior is driven by the progressive development of fabric anisotropy and the formation of interconnected void channels, which enhance hydraulic conductivity and trigger localized instability. Erosion patterns vary across loading conditions. In erosion simulations under biaxial shear conditions, erosion increases monotonically with shear stress. In contrast, under direct and ring shear conditions, erosion is limited during the initial shearing stage due to the reorientation of force chains perpendicular to the seepage direction, which reduces the pore connectivity along the seepage direction and promotes clogging. | en_US |
| dcterms.abstract | Post-eroded specimens exhibit reduced peak strengths, particularly those subjected to high stress states during erosion and those with high fines contents. This reduction is linked to the erosion-induced microstructural damage and the inability to form strong force chains. The residual shear behavior of the post-eroded specimen is most effectively examined under ring shear conditions. Results show that internal erosion leads to a reduction in the residual shear stress, reflecting a permanent loss of interlocking capacity of the post-eroded specimen. More importantly, post-eroded specimens exhibit greater fluctuation amplitudes and reduced fluctuation frequency in the residual shear stress compared to their non-eroded counterparts. This indicates that the deformation mechanism shifts from frequent, small-scale particle readjustments to less frequent but large intermittent slips, which are often associated with localized collapses of coarse-dominated force chains. The formation and development of shear bands are significantly influenced by internal erosion. In direct shear tests, where a 'predefined' shear plane exists, erosion leads to a transition of the shear bands from narrow and localized bands to wider and more diffuse zones, especially in the fine-dominated specimens. This happens because the removal of fines disrupts the original force transmission paths, requiring larger deformation to re-establish stable force chains. In contrast, coarse-dominated specimens, particularly those eroded under low stress states, maintain relatively well-defined shear bands, as the coarse skeleton remains largely intact during the whole erosion stage. | en_US |
| dcterms.abstract | Comparative simulations across different shear loading conditions reveal that both mechanical response and erosion susceptibility are strongly influenced by the shear mode. In biaxial shear specimens, stable and continuous force chains among coarse particles result in the highest peak strengths and the lowest fines mass loss. In direct shear specimens, deformation is confined within a narrow band, producing intermediate strength and erosion resistance. Ring shear specimens, in contrast, involve low confinement together with sustained large displacements, leading to frequent disruption of force chains and the greatest cumulative fines mass loss. | en_US |
| dcterms.abstract | The coupled erosion simulations under hollow cylinder torsional shear conditions can capture the combined effects of principal stress rotation (α) and intermediate principal stress ratio (b). Higher α and b promote anisotropic force chains and reduce vertical pore connectivity of the specimen, further leading to localized clogging. Additionally, key influencing factors on internal erosion such as fines content, hydraulic gradient, and confining pressure are systematically evaluated as part of the erosion simulations conducted under various shear loading conditions. High hydraulic gradients cause rapid fine detachment and early clogging, while low gradients result in gradual erosion. In fine-dominated specimens, this slow process may trigger localized instabilities and rearrangements, increasing the risk of sudden fines loss in later stages. Confining pressure consistently suppresses erosion by enhancing interparticle locking and contact force density, thereby maintaining the granular structure integrity under seepage forces. | en_US |
| dcterms.extent | xxi, 167 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2026 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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