Grain size is an important control on landslide mobility, particularly when mass entrainment is considered. However, field-scale discrete element method (DEM) simulations cannot explicitly resolve individual soil grains, requiring much larger equivalent particles as coarse-grained representations of slope materials. How the equivalent particle size influences the mobility of cohesive, entraining landslides over realistic terrain remains insufficiently understood. To address this gap, we use the 2016 Aso Bridge landslide as a real-terrain reference case and represent the entire slope as a cohesively bonded granular medium, allowing initially stable slope material to fail, become entrained, and contribute to the moving mass. Based on this erodible-slope framework, we conduct controlled virtual landslide experiments with three equivalent particle sizes. The simulations demonstrate that models with smaller equivalent particle sizes produce longer runout, broader spreading, and substantial mass entrainment; using a 2-m travel-distance criterion, the entrained-to-released mass ratio in the smallest-particle model exceeds 45%. The enhanced mobility is observed in both the initially released and entrained masses and is accompanied by higher transient energy-conversion ratios and broader particle travel-distance distributions. The observed equivalent-particle-size dependence is qualitatively consistent with the grain-size-dependent mobility reported for idealized cohesionless granular flows, extending the understanding of such size-dependent mobility to cohesive, entraining landslide systems represented on erodible real terrain. These findings suggest that equivalent DEM particle size is a fundamental modeling parameter that strongly influences simulated landslide mobility, mass entrainment, and energy conversion.

The majority of offshore wind power potential lies in deep waters, where existing anchoring systems are often difficult to install or are not economically viable. A novel Expandable PLate Anchor (ExPLA) has been proposed recently, which can be installed easily in a compact form and which then expands when pulled to maximize bearing capacity. In this study, we systematically examine how the plate geometry affects both the expansion process and the pullout resistance of ExPLA using numerical simulations. Results show that designs enabling rapid opening generally exhibit lower bearing capacity by up to 30% compared to typical cuboid plates. Cuboid plates, in particular, tend to fully open up to 140% later and can experience significant tilting during deployment. Additionally, plates with flat bottoms promote strong mixing between soil layers during expansion. These findings offer useful guidance for optimizing ExPLA plate geometry for holding capacity and installation depth.

Neighborhood algorithms may take a considerable percentage of computer time in discrete element methods (DEM). While the sort-and-sweep algorithm is ideal in some ways, as it only deal with particles whose relative positions change in one coordinate direction, the other directions must be processed too, for all particles. In contrast, tree-codes deal only with adjacent particles. We compare sort-and-sweep and tree-code neighborhood algorithms for two-dimensional DEM simulations of polygonal particles in a rotating drum with up to 12000 particles. We discuss the effects of system size and inlining on the performance with respect to the cache memory. For the tree code, the performance is slightly better, at the cost of significantly increased cyclomatic complexity. In particular, one benefit is improved possibilities for shared memory parallelization.

Intruder mechanics in a granular aggregate is a common subject in engineering and geotechnical applications. However, most studies are limited to spherical intruders or small displacement regimes up to the point of failure. In this work we investigate the vertical pullout of a plate-like intruder buried within a granular aggregate well past the point of failure. We observe a separation of the intruder mechanics into an initial friction controlled regime and a later geometry controlled regime. The transition between the regimes is marked by the emergence of the same friction-independent effective shape of the intruder and a convergence of the resistance force onto the same curve in the post failure regime, independent of the magnitude of friction. Further, during the transition a natural hopper flow develops between the intruder and the aggregate in which material is transported into the void below the intruder by discrete flow events.

Both inter-particle friction and particle shape are known to influence the micro- and macroscopic properties of granular assemblies individually. However their combined influence is still poorly understood. In this work we perform a series of Discrete Element Simulations to systematically study the combined effect of particle angularity and friction on the shear resistance of granular aggregates. We find that for angular particles the residual shear resistance as a function of inter-particle friction shows a local maximum, while for round particles it increases monotonically until it saturates. In contrast, no such effect is observed in the packing structure of the aggregates. The non-monotonic behaviour of angular particles is mirrored by the critical state directional and normal force fabric anisotropies, while the tangential normal force anisotropy shows more similarity to the bulk porosity and the mobilization of friction at the individual particle contacts. Our results now provide a much clearer picture on the origin of the non-monotonic behaviour of the critical state shear resistance on the inter-particle friction, as a competition between sliding and rolling in two different rolling regimes.

Here, we present the energy budget analysis that links seismic focal mechanisms to the development of geological structures in numerical granular rock box experiments, utilizing a discrete element method simulation approach. The model simulates the horizontal shortening of a thin 3D granular rock layer on a geological-scale (100 km x 0.25 km x 2 km), with a maximum element radius of 12.5 m. This simulation reproduces the millimeter-scale fault displacements caused by the rapid and intermittent motions of elements generating elastic waves, that is, virtual earthquakes. The simulation also captures early postseismic processes occurring within several tens of seconds, during which popup structure between the active faults is uplifted. We analyzed over 190 earthquake events during the simulation, with a total shortening length of 14.72 m. The change in energy balance starts with a local fault potential drop that generates the main shock, followed by a regional potential release induced by propagated waves. Statistical analysis reveals positive correlations, ranging from linear to quadratic, between the magnitudes of energy changes and fault slip displacement. Notably, approximately 0.01 % to 60 % of the local contact potential drop in the seismogenic fault is converted into kinetic wave energy, and the efficiency of this conversion increases with the earthquake size. Our results reveal that the uplift energy of the popup structure, which considerably exceeds the wave energy by several orders of magnitude, cannot be explained solely by the local seismogenic fault potential release. Instead, off-fault regional potential release should also be taken into account. We also demonstrate the scaling law for earthquake energy and seismic moment. Our findings suggest that the inherent diversity of virtual earthquakes partially captures earthquake behaviors.

Clay minerals are non-spherical nano-scale particles that usually form flocculated, house-of-card like structures under the influence of inter-molecular forces. Numerical modeling of clays is still in its infancy as the required inter-particle forces are available only for spherical particles. A polytope approach would allow shape-accurate forces and torques while simultaneously being more performant. The Anandarajah solution provides an analytical formulation for van der Waals forces for cuboid particles but in its original form is not suitable for implementation in DEM simulations. In this work, we discuss the necessary changes for a functional implementation of the Anandarajah solution in a DEM simulation of rectangular particles and their extension to cuboid particles.

Clay minerals are non-spherical nano-particles interacting through ranged van der Waals forces. Discrete Element Simulations usually use coarse numerical integration based on sphere clusters, as available analytical formalisms are limited. In this paper, we discuss the numerical implementation of a van der Waals force for cuboid particles derived in previous research. In particular, we describe some of the corrections necessary for its extension to pairs of finite-sized particles.

Intruder mechanics in a granular aggregate is a common subject in engineering and geotechnical applications. However, most studies are limited to spherical intruders or small displacement regimes up to the point of failure. In this work we investigate the vertical pullout of a plate-like intruder buried within a granular aggregate well past the point of failure. While we find the maximum resistance force to depend on the material properties, in the post failure regime the resistance force converges onto the same curve for all friction coefficients. Likewise, the effective geometry of the intruder will always develop the same conical shape on top of the plate, independent of the magnitude of friction, that remains unchanged during the pullout process once established. Further, between the intruder and the aggregate a natural hopper flow develops in which material is transported into the void below the intruder by discrete flow events.

Understanding landslide hazards and developing mitigation measures is critical to protecting lives and property. The Discrete Element Method (DEM) has demonstrated its ability to simulate landslides and estimate impact forces on mitigation structures. Such simulations often model slope surfaces as bedrock on which a fixed amount of earth mass is released and slides. Mass entrainment due to local failure of an excavatable slope surface is rarely modeled with sufficient resolution. Fine-resolution modeling of an excavatable slope for simulation is necessary and non-trivial to improve DEM simulations of large-scale landslides. In this study, we present a method based on Periodic Granular (PG) boxes for efficient modeling of excavatable slopes. A PG box is a packing of particles in a quasi-static state inside a virtual unit box, where the periodic boundary conditions are satisfied at the box surfaces. The procedures used to construct a PG box are presented. The quality of PG boxes is analyzed both at the particle contact scale and at the laboratory specimen scale by measuring contact orientation statistics and by performing numerical triaxial tests. As a demonstration, a centimeter resolution slope model constructed using the PG box-based method is presented using topographic data for the Aso Bridge landslide. In addition, landslide simulations to verify the excavation effect were performed on sub-meter resolution slope models. Our simulations show that landscape shape and particle size have a direct effect on the movement and deposition of earth masses. This highlights the need for detailed 3D terrain modeling and further study of particle size effects. By constructing the first excavatable DEM slope model with billions of centimeter-sized particles, this study can be considered a solid step toward fine-resolution DEM simulations of large-scale landslides, which can contribute to both scientific understanding and engineering countermeasures to mitigate the catastrophic consequences of large-scale landslides.

This study presents virtual earthquake simulation using a numerical granular rock box experiment based on the Discrete Element Method (DEM). The horizontal shortening of a granular rock layer with a thin 3D geometry and periodic boundary conditions generates sequential thrust formation like that of an accretionary wedge. Intermittent fast motions of elements along with faults generating seismic waves are observed through a convergence test following the development of geological-scale structures. This indicates that the granular rock box simulation seamlessly reproduces seismological and geological-scale phenomena. The hypocenter, which is not predefined by the model, emerges within the active fault damage zone and shifts as the geological structures evolve. The seismic event occurs with the shear motion of the fault, characterized by the 3D elementwise rotation and the double-couple behavior, and follows the Gutenberg-Richter law. The quantitative analysis of a virtual earthquake in the main frontal thrust estimates that the fracture propagation speed is - 2.6 km/s, and the Pwave and S-wave velocities are - 3.7 and - 2.7 km/s, respectively. In addition, the slip distance and the mean stress drop at the hypocenter are - 1.8 cm and - 0.46 MPa, respectively, and the major wave frequency is 3-4 Hz. These results show the feasibility of granular rock box simulation for reproducing realistic multiscale mechanisms bridging seismological and geological phenomena. The limitations of the model in terms of fast convergence speed (5 x 10-4 m/s), large element size (similar to 12.5 m), and element shape (sphere) are discussed to achieve a more realistic model.

We investigate the influence of particle angularity on the stress–strain behaviour, rotation and micromechanics of granular assemblies under plane strain condition. Granular particles are modelled as regular polygons and numerical biaxial compression tests have been performed using the discrete element method. The packings consist of regular polygons with increasing corner number ranging from 5 to 64. The packings are analysed in the critical state in terms of their shear strength, bulk friction angle and porosity, as well as their cumulative rotation and contact characteristics with respect to varying particle angularity. We find that packings of more angular particles are looser but have higher shear strength, while packings of more rounded particles are denser, but are less resistant to shear. We further show that packings of angular particles are more resistant to reorganization by rotation, and that the mean rotation magnitude saturates at a constant value with increasing roundness. Lastly, we find that packings of more angular particles tend to have less contacts with higher normal and tangential forces when compared with packings of more rounded particles.

Studying the collective behavior of adhesive particles with the discrete element method (DEM) requires well-founded force–displacement relations (force models). While the Johnson–Kendall–Roberts (JKR) theory reliably predicts the dependence of the contact radius a on the force F, it has remained a challenge in this framework to obtain a straightforward force–displacement relation F(δ) with physically meaningful parameters to calculate the force F from the displacement δ. We derive a novel force–displacement relation from the JKR theory as a composition of functions F(δ)=(F∘a∘λ)(δ), with the intermediate functions contact radius a(λ) and effective adhesive contact radius λ(δ). We also analyze contact geometry errors in the Hertz and JKR models, derive the exact contact centroid to accurately calculate contact torques and relative tangential velocities, and propose a smoothed JKR model to avoid discontinuities in force and energy. We find that incorrect torques and relative tangential velocities are obtained when the stiffness quotient is neglected because it affects the exact location of the contact centroid. We also find that contact geometry errors can become non-negligible for nanoparticles due to their large relative contact size. In addition, we show from bouncing ball simulations that the JKR models with a nominal coefficient of restitution derived for the Hertz model result in higher damping and thus reduced actual coefficients of restitution. Our analysis serves as a foundation for contact-mechanics-based force models for DEM simulations of adhesive particles to investigate their collective behavior in the future.

A numerical granular rock box experiment based on the Discrete Element Method (DEM) was performed in thin 3D geometry to investigate the role of granularity in thrust formation. This rock box experiment is an extension of the numerical sandbox test, which is considered an analog experiment for accretionary prism formation with cohesive contact force. The parameters of contact-based interaction are adjusted to account for the failure envelope of the host rock in the triaxial test. The developed model allows the numerical simulation of the horizontal shortening of a granular layer on geologically relevant scales. The rock box test successfully reproduces the characteristic structures of accretionary wedges developed during sequential thrust formation. In contrast to the non-cohesive case, the cohesive models generated a surface geometry with steeper angles, surface vertical faults, and enhanced bifurcation of the shear bands. The geometric network of fault planes depended on the healing of the cohesive force within the faulted region. The increasing complexity of the network was demonstrated using finer elements until its maximum radius reached 12.5 m. We also evaluated the granular nature of the thrust thickness, which was found to depend on the number of frictional elements rather than physical length. A decrease in the growth rate of the fault damage zone thickness with increasing fault displacement was found to be consistent with observational data. Our results suggest an important role for granularity in thrust evolution.

Shapes of constituent particles have a prominent effect on the macroscopic responses of granular assemblies. Clayey minerals often possess a plate-shaped geometry with a large surface-to-volume ratio. It is difficult to model such a geometry with spheres or clusters of spheres in a conventional discrete element method (DEM). In this study, we present a new DEM for plate-shaped particles with a focus on particle geometry and kinematics. The moment of inertia for a general convex plate is given and unit quaternions are adopted to represent the angular degrees of freedom. In addition, the equation of motion for rotation is proposed to be solved in a body-fixed rather than in a space-fixed reference frame. We present simulations of the rotation of a system of plate-shaped particles under the conservation of angular momentum without external torque. The results demonstrate the necessity and importance of enforcing the unity constraint on the quaternions numerically solved from the equation of motion for rotation.

Mixing processes are commonly used to handle powders and grains in several industrial fields, and their performance has been subjected to extensive study. However, research is limited on underwater mixing in novel deep-sea mining applications. Consequently, we adopt a discrete element method (DEM) enhanced by a lubrication model to investigate the underwater mixing process. We focus on the effect of microscopic material parameters on macroscopic mechanical responses in this study. Variations in macroscopic responses are small among DEM samples with a well-controlled initial density; the largest coefficient of variation (cv) is less than 1.4% in normalized forces on the sidewall, and the values of cv are less than 1.0% for other macroscopic responses. A comprehensive parametric study is conducted for elastic moduli and for dissipative parameters. Elastic moduli exhibited a negligible influence, and the effects of dissipative parameters ranged from most significant to most negligible in the order of coefficient of rolling friction, coefficient of friction, coefficient of restitution, and fluid viscosity. We further discuss the network connectivity of force chains and shear-induced size segregation; it was found that an increase in rolling friction increases the connectivity of particles in principal stress chains, which increases the mixing resistance. Size segregation is monitored for DEM samples with particles that initially follow a uniform size distribution: an increase in friction is observed to enhance the segregation and an increase in fluid viscosity to alleviate it. The findings in this paper can advance the understanding of the dynamics of underwater mixing and offer insights for designing mixing systems for granular materials with large variations in material properties.

We investigate the avalanches of spherical and non-spherical granular particles inside half-filled rotating drums. The time series of the center of gravity of the particle assemblies are obtained via image analysis and their single-sided amplitude (SSA) spectra are analyzed. The spectra features of this new indicator turn out to be characteristic for the avalanches, in terms of the existence of peaks in the low-frequency range and the decay rate of high frequency components. The SSA spectrum has a peak for the packings of non-spherical particles but not for the spherical particles. The high frequency part is characterized by a power law decay 1/ f a (a > 0) . A 1/ f -decay is found only for the spherical particles. For the packings of cornered particles, the exponents significantly deviate from a = 1. As 1/ f spectra are often associated with self-organized criticality and therefore a scale invariance of the dynamics, we may conclude that there is no scale-invariant structure for granular avalanches. Considering the small number of particles and the regularity of convex particle shapes being used, the spectral features revealed in this study could be utilized for validating particle simulations.

As a follow-up of an earlier work on the numerically exact Coulomb friction in two-dimensional simulations, we present here the relations and implementation for three-dimensional discrete element particles.