Influence of fine-coarse content on settlement behavior of overburden dumps under surcharge loading

Abstract

Long-term stability of coal mine overburden (OB) dumps is highly dependent on their mechanical response under surcharge loading, yet consolidation-induced deformation is often neglected in stability evaluations. In this study, laboratory experiments were performed to investigate the gradation-dependent settlement, void ratio evolution, and dielectric behavior of saturated OB materials. Three different mixture combinations of fine sand (FS) and coarse sand (CS) of OB material in proportions of 30 %FS:70 %CS (M1), 50 %FS:50 %CS (M2), and 70 %FS:30 %CS (M3) were considered to understand settlement behavior under incremental surcharge loading. A noninvasive time-domain reflectometry (TDR)-based monitoring scheme was employed to track dielectric permittivity, volumetric water content (VWC), bulk unit weight, and porosity during consolidation. Settlement for M1 was 18.32 mm, increasing by 52.45 % from M1 to M3. Fine-rich mixtures exhibited greater settlement and slower consolidation due to higher initial void ratios and water retention, whereas coarse-dominated mixtures showed lower settlement and faster stabilization owing to efficient drainage and particle interlocking. Bulk unit weight increased while void ratio decreased with loading, with reductions of 29.26 %, 35 %, and 41.59 % for M1, M2, and M3, respectively. Strong correlations between dielectric permittivity and volumetric water content were modeled using third-order polynomials and sigmoid functions (R2 &gt

0.85) for all mixtures. Dielectric mixing analysis revealed that the formation factor increased with decreasing porosity, reflecting particle rearrangement under load. These results highlight the role of particle size distribution in hydro-mechanical coupling of overburden and demonstrate the potential of TDR-based monitoring to incorporate gradation-specific consolidation parameters into predictive models for safer dump design. © 2025 Elsevier B.V., All rights reserved.