In the realm of geomechanics and material science, understanding the hidden interactions within granular materials under stress has always posed a formidable challenge. A newly published study by Zhang, Konietzky, and Song brings groundbreaking insights into this complex domain by investigating the evolution of force networks, contact networks, and tensile force chains in rock-like bonded granular materials subjected to both unconfined and confined compression. Their research, published in Environmental Earth Sciences in 2025, leverages advanced Discrete Element Method (DEM) simulations to peel back the layers of complexity governing how these materials respond structurally to external loads. This study not only enhances our fundamental knowledge but also paves new pathways for engineering applications ranging from mining to earthquake resilience.
At the heart of granular material mechanics is the understanding that these substances are not homogeneous solids, but intricate assemblies of discrete particles bonded together in a matrix that behaves collectively under stress. Traditional continuum mechanics approaches often fall short in capturing the intricacies of these interactions. The team’s application of DEM—a computational method that models each particle and the forces exchanged between them—enables a high-fidelity reconstruction of microscale dynamics invisible to conventional analysis. By simulating rock-like materials under different compressive conditions, the researchers reveal how force transmission networks evolve spatially and temporally, offering a dynamic picture of internal stress redistribution that governs macroscopic behavior.
One of the most significant contributions of this work is the detailed characterization of how the force network reorganizes during compression. In both unconfined and confined states, the granular assemblages respond by adapting their internal force chains—linear paths that carry disproportionately high tensile or compressive loads. In unconfined compression, force chains tend to localize and orient along preferential directions, leading to eventual failure planes. Conversely, under confined compression, the presence of lateral pressure alters the mechanical environment markedly, fostering a more distributed network of force transmission that enhances the material’s overall stability. This dual perspective is crucial for engineering applications since many geological processes involve variations in confining stress.
The contact network, describing the direct points of connection between particles, is another critical aspect rigorously analyzed in the study. Beyond mere adjacency, contacts transmit forces that can be either compressive or tensile depending on the loading state and particle bond characteristics. Zhang and colleagues elucidate that the evolution of these contact points is not static but dynamically reshaped as compression progresses, influencing the rearrangement of force chains. The interplay between contact persistence, breakage, and formation under varying confinement levels drives the transition from elastic behavior to irreversible damage and eventual failure. Such microscopic insights have profound implications for predicting material strength and fracture patterns.
A particularly novel element of their findings lies in the exploration of tensile force chains within bonded granular materials. Unlike compressive forces, tensile forces carry a distinct risk for the initiation and propagation of cracks since rock-like materials tend to be weak in tension. The DEM simulations unveil how these tensile chains emerge, evolve, and sometimes reconnect to form complex load-bearing architectures that counterbalance compressive stresses. This delicate balance dictates the onset of microcracks and their coalescence into macrofractures, thus influencing the failure mechanisms of geological materials. Understanding tensile chain dynamics opens a new frontier in anticipating catastrophic failure points.
The study also delves into the effects of particle bonding properties on the mechanical response. Since natural rock and engineered granular materials have bonds of varying strengths and stiffnesses, modeling these parameters explicitly offers insights into realistic scenarios. The researchers systematically vary bonding parameters within their DEM framework, observing how stronger bonds contribute to the sustainability of tensile force chains and extended connectivity within the network. This dependency suggests that tailored bonding conditions could be engineered to optimize material resilience, offering promising ideas for industrial enhancement or geotechnical remediation.
Moreover, Zhang et al. provide comprehensive temporal analyses highlighting how the evolution of force and contact networks is not instantaneous but follows distinct phases during the compression process. Initially dominated by elastic deformation, the granular assembly gradually shifts into a regime characterized by bond breakages and network reconfigurations. The temporal progression captured through DEM simulations adds a kinetic dimension to our understanding, emphasizing that the peak strength and failure initiation are functions of both spatial organization and loading rate. Such time-dependent behavior is critical for dynamic loading conditions encountered in earthquakes or blasting operations.
Their use of visualization tools further accentuates the clarity of these complex interactions. By rendering three-dimensional force chains and contact points at successive intervals, the researchers offer a visually intuitive grasp of internal mechanisms. These graphics vividly illustrate how localized force concentrations evolve into system-spanning networks or conversely degrade into isolated fragments during failure. Such visualizations not only enhance scientific comprehension but also serve as compelling storyboards for communicating findings to broader audiences, including engineers, educators, and policymakers.
Another dimension addressed in the study is the role of confinement level on fracture pattern development. The transition from brittle to ductile behavior under increasing lateral confinement is captured with precision, revealing that confining pressure retards damage initiation and promotes distributed cracking. This finding reinforces empirical observations from rock mechanics while providing a mechanistic underpinning via DEM. The ability to simulate these effects at the particle scale arms geotechnical engineers with predictive tools essential for designing safer underground excavations, tunnels, and slope stabilization measures.
Zhang and colleagues also discuss the implications of their findings for natural hazard mitigation. Earthquakes often trigger sudden failure in granular geological materials, and understanding how internal force structures evolve before catastrophic collapse may help identify precursors or vulnerabilities in rock formations. The detailed snapshots of force network evolution prior to failure could inform monitoring strategies using acoustic emissions or other geophysical sensing techniques. Such translational potential elevates DEM studies from purely academic exercises to vital components of disaster risk management.
The integration of bond breakage modeling into their DEM framework is another highlight, enabling the simulation of crack initiation and propagation realistically. Rather than treating granular materials as rigid clusters, the model accounts for progressive degradation, mimicking natural fracture evolution under stress. This breakthrough allows researchers to capture not only the peak load-bearing capacity but also post-failure behavior, crucial for understanding residual strength and post-collapse stability. The continuous transition between intact and damaged states embedded in this model enhances the predictive fidelity of numerical simulations.
In addition to mechanical insights, the study sheds light on microstructural heterogeneity’s influence on material response. Natural granular materials seldom exhibit uniform particle size, shape, or bonding distribution. By incorporating realistic heterogeneity within their models, the team observes emergent behaviors such as localized damage zones and uneven force chain distribution that closely match real-world observations. This alignment legitimizes DEM as a powerful tool for bridging microscale phenomena with macroscale material properties and contributes to the ongoing refinement of constitutive models in geomechanics.
This research also underscores the importance of multidisciplinary collaboration in advancing our understanding of granular materials. The intersection of computational physics, material science, earth science, and engineering is vital for tackling such multifaceted problems. Zhang, Konietzky, and Song’s work exemplifies how leveraging expertise in numerical methods, rock mechanics, and data visualization can generate comprehensive narratives about complex material behavior, fostering innovation in both academic and applied sectors.
Looking ahead, the methodologies and insights from this study set the stage for more sophisticated investigations incorporating thermal effects, fluid infiltration, and chemical degradation within granular matrices. These factors critically influence rock strength and failure mechanisms in natural settings like geothermal reservoirs or oil extraction fields. Extending DEM frameworks to model coupled multi-physics phenomena will enhance our capacity to predict and manage geological systems under increasingly variable environmental conditions.
Ultimately, the pioneering work by Zhang and colleagues redefines our approach to understanding bonded granular materials’ mechanics under compression. By illuminating the dynamic evolution of force and contact networks and articulating the fracture behavior of tensile force chains, this study provides a robust foundation for both theoretical advancements and practical applications. As computational power and modeling techniques evolve, such detailed microscale investigations will become linchpins in the quest to engineer safer structures, optimize resource extraction, and mitigate natural hazards through deeper insight into the microscopic secrets of rocks.
Subject of Research: Evolution of force networks, contact networks, and tensile force chains in rock-like bonded granular materials under compression conditions.
Article Title: Evolution of force network, contact network, and tensile force chains in rock-like bonded granular materials under unconfined and confined compression: A DEM study.
Article References:
Zhang, M., Konietzky, H. & Song, Z. Evolution of force network, contact network, and tensile force chains in rock-like bonded granular materials under unconfined and confined compression: A DEM study. Environ Earth Sci 84, 320 (2025). https://doi.org/10.1007/s12665-025-12288-z
Image Credits: AI Generated
