Internal erosion is a primary cause of instability in transportation embankments and subgrades. This study investigates the erosion susceptibility of five poorly graded quartz sand specimens under constant and cyclic hydraulic gradients. The specimens consist of two gap-graded sands and three continuously graded sands, with maximum particle sizes (Dmax) ranging from 2 to 5 mm and coefficients of uniformity (Cu) ranging from 6.8 to 10.8. The analysis combines laboratory tests with coupled computational fluid dynamics and discrete element method simulations (CFD–DEM). A high gradient was applied representing seepage in flood-inundated transportation embankments and their foundations. At this gradient, no single geometric criterion ranked the susceptibility; the controlling parameter was gradation-family-dependent: the erosion ratio decreased with increasing Cu for the continuously graded soils but increased with increasing Dmax for the gap-graded soils, both trends consistent with control by the pore constriction size relative to the mobile fines. The lowest-Cu sand (6.82) had the highest erosion ratio, 9.9
Current studies on diffuse instability in binary mixtures have predominantly focused on macroscopic mechanical responses, while the underlying particle scale mechanisms, particularly the roles played by different contact subnetworks, remain insufficiently understood. In this study, a series of constant shear drained (CSD) tests on binary mixtures with varying fine content and relative density are conducted using the discrete element method (DEM), aiming to systematically investigate the contributions of contact subnetworks to the triggering of diffuse instability. From a macroscopic perspective, the stress ratio at the onset of instability exhibits a non-monotonic trend with increasing fine content, first increasing and then decreasing. The trend is primarily governed by the anisotropy of contact normal and the anisotropy of normal contact force. From the perspective of subnetworks, the variation in their contributions to the deviatoric stress with fine content is generally consistent with the evolution of coordination number. By introducing the coordination number, mean contact force, and mean branch vector length, a stress-force-fabric relationship for subnetworks is established, which effectively characterizes the evolution of the stress ratio. In the underfilled and interactive-underfilled regimes, the tangential contact force anisotropy reaches the fine content threshold for dominant contact type transition first, followed by the of normal contact force anisotropy, while the contact normal anisotropy reaches the threshold last. In the interactive-overfilled regime, the sequence of these thresholds is reversed. Furthermore, the influence of fine content on the evolution of subnetwork anisotropy exhibits a pronounced lag compared to its effect on the contribution to deviatoric stress.
The stability of confined multi-element systems under rotational loading presents a challenge that is not adequately captured by classical single-body formulations. In assemblies of slender elements, internal contact interactions introduce additional resistance mechanisms that can influence stability. This study develops a computationally supported framework for analyzing the rotational stability of hand-held slender-rod bundles by incorporating internal jamming and twisting friction mechanisms. The proposed model extends classical centripetal-force-based stability relations by introducing an effective resistance term associated with inter-rod contact interactions. The resulting formulation describes critical stability conditions in relation to grip force, angular velocity, bundle size, and frictional properties. Numerical evaluation and computational parametric analysis were conducted to examine the model response over a range of parameter values. A dimensionless stability formulation is introduced to facilitate analysis of the governing relations and comparison between configurations within the model’s assumptions. Controlled experiments were performed using steel nail bundles containing 5–20 elements, with grip force measured using a calibrated sensor and angular velocity obtained from high-speed video analysis. The onset of instability was identified by observable relative slip between rods exceeding the predefined experimental threshold, rod ejection, or bundle disintegration during progressively increasing rotational speed. The measured critical angular velocities exceeded the predictions of the classical formulations for the investigated configurations. Comparison of model predictions with experimental measurements, using the coefficient of determination, root-mean-square error, and mean absolute error, was used to quantify the level of agreement. The model introduces a jamming efficiency parameter to represent the contribution of internal contact interactions to collective resistance. The results indicate that internal jamming and twisting friction can contribute to enhanced rotational stability and are associated with regime-dependent behavior in multi-element systems. The framework provides a basis for further investigation of rotational stability in confined multi-element assemblies, with potential relevance to grasp mechanics, granular physics, and multi-element gripping systems.
Particle breakage is a major mechanism responsible for the degradation of coarse-grained soils, yet the effect of particle morphology on single-particle crushing strength remains insufficiently quantified. In this study, 362 landslide-debris particles were grouped into three size fractions (13–20, 20–27, and 27–34 mm) and three morphological categories (blocky, flaky, and pointed). Single-particle compression tests were performed using an MTS high-performance fatigue testing machine. Before loading, multi-angle images were processed in MATLAB to determine the elongation index, flatness index, circularity, convexity, sphericity, and form factor of each particle. The results show that, for particles within the same size fraction, blocky particles generally exhibit the highest fracture force. Under the adopted Lee definition (σc = F/d²), blocky particles also show the highest crushing strength, whereas pointed particles show the lowest. The crushing strengths of all three particle types are well described by a Weibull distribution, and the characteristic crushing strength decreases with increasing particle size, indicating a size effect. Three characteristic force–displacement responses and corresponding failure modes—splitting fracture, multi-fragment fracture, and crushing fracture—were identified. The findings indicate that particle morphology is associated with differences in the magnitude and variability of crushing strength and in the dominant failure mode. These results provide experimental evidence of morphology-dependent particle breakage in coarse-grained geomaterials, particularly landslide-debris deposits.
Manual analysis of high-speed images is time-consuming and subject to operator-dependent errors when quantifying cereal-kernel impact-breakage parameters. This study presents a high-speed image-based framework for controlled single-kernel impact tests. The framework combines YOLO-MRPD (MobileNetV4–RFAConv–P2–DySample), a task-adapted YOLOv11-based detector, with ByteTrack-based multi-object tracking so that fragments and the striker can be detected, target identities can be maintained across consecutive frames, and breakage degree can be quantified and striker kinetic-energy loss can be estimated. YOLO-MRPD integrates MobileNetV4, receptive-field attention convolution (RFAConv), a P2 detection head, and DySample for the present imaging task. Detection metrics were averaged across five independent training runs. For maize kernels, the model achieved precision, recall, and mean average precision at an intersection-over-union threshold of 0.5 (mAP50) values of 95.3
