Size-related bond mechanical parameters in DEM for simulating the failure of rock with complex pore structure

To investigate the mechanical properties and damage evolution of fissure sandstone under the interaction between water and fissures, this study performed uniaxial compression tests on sandstone specimens with different water conditions (dry, natural, and saturated) and fissure angles (0°, 30°, 45°, 60°, and 90°). The experimental results indicate that peak strength decreased markedly with increasing water content, with reductions of 28.68%–53.99% under saturated conditions relative to dry conditions. In contrast, peak strength increased progressively with fissure angle. Crack initiation stress and crack damage stress exhibited similar trends. Based on the normalized ratios of characteristic stress, two damage evaluation indices, and , were proposed to characterize the weakening effect of fissures on rock bearing capacity during the crack initiation and crack propagation stages, respectively. The energy evolution results show that the strain energy corresponding to characteristic stress decreases significantly with increasing water content and generally increases with fissure angle. In addition, this study introduced a warning coefficient λ based on the ratio of elastic strain energy to dissipated strain energy to identify precursor information associated with rock failure. The results show that λ increased with water content and varied with fissure angle in an M-shaped pattern, with significant peaks at 30° and 60°. Under saturated conditions, water exerted the strongest effect on mechanical parameters at a fissure angle of 0°, while the overall effect remained relatively small at 30°. These findings provide a valuable reference for risk assessment and disaster prevention in geotechnical engineering.

ABSTRACT Rock bursts pose a significant challenge in deep hard rock tunnel engineering. This study investigates the energy evolution during rock failure through uniaxial upper-limit loading and unloading tests, establishing a connection between rock energy storage characteristics and rock burst tendency. True triaxial loading tests on tunnel models are employed to analyse the relationship between stress paths, rock stress magnitude, and rock bursts. By integrating the rock’s energy storage properties and the stress conditions within the rock mass, a new evaluation index, Stress and Energy Storage Density (SESD), is proposed to assess the rock burst tendency. A case study on rock burst during double-shield TBM excavation reveals that the disaster incubation process progresses in six stages: elastic state, crack initiation, crack propagation, fragment ejection, slab fracture buckling, and unstable failure. The SESD index incorporates both rock strength and energy dynamics, capturing the stress state during excavation and the associated energy accumulation-release process in surrounding rock. Numerical results show that SESD variations closely match actual rock burst occurrences, validating their effectiveness in simulation-based analysis. This study introduces a novel energy-stress coupled method for rock burst prediction, offering clear modelling principles, practical applicability, and robust adaptability for complex engineering scenarios.

Volcanic eruptions often result from the failure of rocks surrounding magma pathways. A decrease in b-value typically precedes such failures, indicating increased stress and eruption likelihood. Here, we analyze b-value time series of seismic data from 8 well-monitored volcanoes across various tectonic regions: Eyjafjallajökull, Fagradalsfjall, Grímsvötn, and Holuhraun (Bárðarbunga) in Iceland; Mauna Loa in Hawaii (USA); and Kirishima, Ontake, and Usu in Japan. We introduce a 'Volcano Traffic Light Alert System (VTLAS)' to assess priming timescales and potential improvements to near‑real‑time forecasting. We define red light as instances when the b-value drops exceed 10% below normal background levels of activity and examine whether eruptions occur within 10 days. Of the 25 identified cases, 39% are followed by eruptions, whereas 61% are not. Among the latter, 71% involve red lights without subsequent eruptions but are mostly linked to large earthquakes, and 29% show no drop before an eruption. Despite the relatively low percentages, our forecasting success rate is comparable to that reported in studies employing InSAR, GNSS deformation, or thermal anomaly analyses. This suggests that the proposed VTLAS may help anticipate impending eruptions. However, to improve reliability, we recommend combining b-value analysis with other geophysical observables to effectively distinguish volcanic unrest from imminent eruptions.

Three-dimensional numerical investigation of blast-induced rock failure under in-situ stress using the material point method

Earthquake-induced collapses of steep cliffs with hazardous rock masses are a prevalent geological hazard in mountainous regions. Current methods for assessing the stability of grouped rock failures under seismic loading exhibit significant limitations. This study introduces an integrated multi-scale methodology combining scaled shaking table tests with 3DEC discrete element numerical modeling to systematically investigate the failure modes, critical collapse thresholds, and risk factors for hazardous rock formations along the China-Pakistan Highway. The approach uniquely bridges physical experimentation, numerical mechanistic analysis, and data-driven prediction to decipher complex failure mechanisms, with a focused analysis on toppling collapse. Key findings include: (1) a displacement angle threshold of ≈ 15° serves as a robust collapse indicator, outperforming conventional metrics; (2) the degree of rock weathering (fragmentation) exerts a dominant control on stability compared to joint inclination, height, and strength; (3) a developed BP neural network model effectively identifies toppling and sliding as the two predominant failure modes, utilizing joint inclination as a key discriminant; (4) collapse initiation shows a nonlinear dependence on rock geometry, where failure is accelerated by increased joint inclination or decreased rock size. Furthermore, a critical vibration velocity is established as a practical criterion for predicting toppling collapse. Factor importance analysis ranks the influencing parameters in the order: rock size > joint inclination > shape > layering configuration. The proposed thresholds, predictive criterion, and neural network model provide directly applicable tools for early warning and risk assessment, offering a refined theoretical and practical framework for mitigating seismic rockfall hazards in earthquake-prone regions.

Analysis of macro–micro mechanisms and influencing factors of composite rock failure under excavation disturbance

HighlightsWhat are the main findings?An energy-envelope-based segmentation strategy is developed to separate dense and overlapping AE waveforms without relying on fixed timing parameters.A multi-indicator template sliding-window identification scheme (correlation, ring count, rise time, and energy) is proposed to detect rock-failure-related AE events and refine arrival picking via time-difference correction.What are the implications of the main findings?The proposed workflow improves AE event detection and picking reliability under strong attenuation, non-stationarity, and missing-channel recordings, enabling more accurate localization in rock failure tests.The method provides a practical foundation for real-time damage monitoring and early-warning of rock instability in geotechnical engineering applications.With the widespread application of acoustic emission (AE) technology in geotechnical engineering, effectively separating and identifying dense AE signals generated during rock fracturing remains a critical challenge. This study proposes an AE event identification technique based on waveform energy envelopes and multi-indicator characteristic parameters. First, the waveform energy envelope is used to adaptively segment dense and partially overlapping AE waveforms without relying on fixed timing parameters. Then, a template sliding-window scan integrating waveform correlation, ring count, rise time, and signal energy is performed to identify candidate AE events. In addition, a time-difference correction and window-stacking strategy is adopted to improve multi-channel arrival picking. Experimental validation on representative single-peak single-event and double-peak multi-waveform cases extracted from laboratory rock-failure tests demonstrates that the proposed method can effectively separate and identify AE waveforms under the tested conditions. Compared with conventional timing-parameter-based segmentation and correlation-dominated matching, the proposed workflow is more robust to waveform attenuation and distortion. The method provides a methodological basis for AE waveform identification and arrival-time extraction in rock-failure monitoring and has potential to support early warning after further validation.

Accurately simulating the post-peak behavior of brittle rocks remains a challenge for statistical damage constitutive models. This study investigates the sensitivity of post-peak simulation to model components by evaluating combinations of three strength criteria and three micro-element strength distributions against triaxial test data from five rock types. Results indicate that the probability distribution of micro-element strength governs simulation accuracy, while the strength criterion exerts minimal influence. Based on these findings, a relative brittleness index-based method for selecting the optimal distribution is proposed, along with a dual-parameter collaborative correction method. Validation shows that this approach significantly enhances the fit to experimental post-peak curves, eliminates criterion-induced interference in parameter adjustment, and remains effective across multiple distribution modes. The proposed method offers a solution for improving the reliability of damage models in predicting brittle rocks failure.

The phenomenon of progressive failure, stress and wave velocity asynchrony in rocks can inform early warning approaches for rock stability. In this study, the Geotechnical Consulting and Testing Systems rock triaxial test system was used to investigate the compression failure of sandstone from the Ningtiaota mine under confining pressures of 0, 2, 5, and 10 MPa, with synchronous ultrasonic wave velocity monitoring. Based on Martin’s crack strain theory, the variation laws of mechanical and wave velocity response characteristics during progressive failure were obtained from two replicate tests per confining pressure. The results indicate that the normalized stress at peak wave velocity σvmaxP/σf ranges from 0.84 to 0.99, whereas the normalized strain ranges from 0.73 to 0.98. With increasing confining pressure, both the strain and stress differences between the peak wave velocity and the peak stress increase. Wave velocity change results from the combined action of effective stress (promoting velocity increase) and crack strain (leading to velocity decrease), causing the wave velocity peak to occur ahead of the stress peak. The normalized crack initiation stress σci/σf ranges from 0.55 to 0.68, and the normalized crack damage stress σcd/σf ranges from 0.79 to 0.91, consistent with literature values for intact sandstones. With increasing confining pressure, the proportion of the compaction stage remains unchanged, while the stable crack propagation stage decreases, and the elastic and unstable crack propagation stages increase. The stress-normalized difference between the peak wave velocity and the damage variable protrusion point is approximately 0.1σf, showing a slight decreasing trend with increasing confining pressure.

High-geothermal tunnels are subjected to complex thermo–hydro–mechanical (THM) coupling effects, where the interaction of temperature, seepage, and stress significantly influences the stability of surrounding rock. To address the limitations of conventional models assuming uniform initial temperature, a THM-coupled numerical model incorporating an in situ temperature gradient is established based on the Sangzhuling Tunnel. The concept of the thermal influence zone is quantitatively defined by an equivalent-radius method, and its spatiotemporal evolution is systematically investigated. In addition, the distinct roles of temperature and pore water pressure in controlling deformation and plastic-zone evolution are comparatively clarified. The results show that the thermal influence zone expands nonlinearly with increasing initial rock temperature and gradually stabilizes over time. Temperature and pore water pressure both promote the development of the plastic zone, which predominantly propagates along directions approximately 45° to the horizontal. Under the geological and boundary conditions considered in this study, temperature plays a dominant role by inducing thermal stress and degrading mechanical properties, leading to significant expansion of the plastic zone and increased vault deformation. In contrast, pore water pressure mainly reduces effective stress, thereby influencing deformation distribution, especially at the tunnel invert. Overall, THM coupling significantly amplifies surrounding rock failure compared with single-field conditions. The findings provide quantitative insights into the evolution of the thermal influence zone and its coupled control on deformation and plasticity, offering a theoretical basis for support design and stability control in high-geothermal tunnels.

Rocks release subtle geochemical warning signals before breaking. These signals, coming from naturally occurring nuclides (e.g., radon, helium, argon, and thoron), have often been reported before earthquakes, volcanic eruptions, landslides, and rock and ice avalanches. However, despite their high sensitivity to deformation, their detectability, as well as myriad promising observations over half a century, nuclide signals are still far from being applied to geohazard prediction or widely used for monitoring. Here, we first develop a decomposition and interpretation method for nuclide signals. By analyzing nuclide signal time series observed from a month-long laboratory rock failure experiment and year-long slope deformation in a field setting, we identify a universal paradigm unit of nuclide signal evolution. We find that this paradigm unit is characterized by two core characteristics: a transient pulse and equilibrium fluctuation which are intrinsically correlated to rupture area and crack aperture, respectively. Through analytical derivation and pore-scale simulations, we establish the constitutive equations that link these characteristic nuclide signals to key rupture structural parameters. Rooted in these constitutive relations, we further develop a diagnostic theory of rock rupture via nuclide signals. We apply the model to track rock failures at the laboratory and field scale. The proposed nuclide signal decomposition and rupturing model enable the unification of discrete signal units emitted by individual microrupturing events, with the integrated signal evolution observed during macroscopic failure. This integration may serve as a foundation for both the mesoscopic assessment of rock damage and the early warning of geohazards induced by rock ruptures.

Rock Failure Characteristics Under Dynamic Indentation Tests of Granite Pretreated by Microwave Heating

Abstract To study the instability deformation law and acoustic emission response characteristics of rocks under loading, compression experiments were conducted on the rock specimens under single-axis loading. The mechanical parameters of rock failure and the characteristic parameters of AE (acoustic emission) response were recorded by a full-information acoustic emission instrument. The numerical simulation of this process was carried out with PFC. The research results show that the evolution traits of the number of acoustic emission location events can reflect the degree of rock damage and failure, and the spatio-temporal evolution characteristics can reflect the actual failure process of rocks. During the loading process, there is a good correspondence between the failure process of the rock specimen and the acoustic emission response characteristics. When the stress changes suddenly (suddenly increases or decreases), the accumulated number of AE ring count and the cumulative energy of acoustic emission both increase sharply. The cumulative ringing count and cumulative energy of acoustic emission increase sharply, but the stress does not necessarily change suddenly. The results of laboratory experiments and numerical simulations were compared and verified to explain in depth the failure and deformation laws of rocks and the acoustic emission response characteristics. According to the acoustic emission response characteristic parameters, a quantitative model of acoustic emission signals and damage was established, further revealing the failure behavior of rocks. The research results provide a new idea for the study of rock damage mechanisms and offer references and inspirations for other geotechnical engineering fields or similar problem areas.

To meet the increasing demands of construction, rock engineering has become a hot topic in modern engineering. Notably, the tensile failure of rocks still significantly affects the safety of rock engineering. Discontinuous deformation analysis (DDA), an implicit discrete-element method, is well-suited for modeling the deformation behavior of blocky rock masses. To investigate the role of mineral grain characteristics in the initiation, propagation, and coalescence of microcracks during tensile loading, in this study, a statistically representative Voronoi grain-based model was developed within the DDA framework (GB-DDA). After the model was calibrated using mesoscopic parameters, the GB-DDA approach demonstrated strong agreement with experimental results for Barre granite under both tensile and compressive conditions, enabling a detailed quantitative analysis of intragranular and intergranular damage evolution. To further evaluate the effects of mesoscopic heterogeneity on tensile behavior, some GB-DDA numerical models were constructed by varying the average grain size, grain roundness, and mineral content. Under the quasi-static Brazilian splitting condition, the simulations revealed a consistent order in crack types, with intergranular tensile cracks occurring most frequently, followed by intragranular tensile cracks, intergranular shear cracks, and intragranular shear cracks. Among them, the failure process was overwhelmingly dominated by tensile cracking. The results showed that an increase in average grain size or biotite content and a reduction in grain roundness led to a notable decrease in Brazilian tensile strength. Larger grain size and lower grain roundness promoted earlier crack initiation and resulted in a more uniform angular distribution of tensile cracks. In contrast, variations in biotite content had little effect on the timing of initial cracks or orientation of tensile cracks. Additionally, the occurrence of intergranular cracks was promoted by increases in average grain size, grain roundness, and biotite content.

Dilation dominates the Changbaishan volcanic basalt rock failure process under uniaxial compression

Discrete Element Method for Investigating the Borehole Wall Rock Failure Process Based on the Enhancement Effect of Microbial Drilling Fluids

With the intensifying depletion of coal resources, water hazard prevention and control for confined coal seam mining—characterized by ultra-thin aquicludes in both roof and floor adjacent to dual confined aquifers—has become a critical challenge. Taking the 9101 working face of Mine A as the research object, this study aimed to address the complex geological conditions of dual ultra-thin aquicludes and dual confined aquifers. Through FLAC3D numerical simulation, we compared the surrounding rock deformation and failure characteristics of four mining schemes, namely Fully Mechanized Coal Mining, Regional Grouting Mining, Backfill Mining, and the Coupled Application of Regional Grouting and Backfill Mining, and further evaluated their applicability for water hazard prevention. The results demonstrate that each single scheme has inherent limitations, whereas only the coupled scheme can achieve synergistic control of roof and floor water hazards. Specifically, after implementing the integrated prevention and control system of Regional Grouting Mining – Backfill Mining – Structural Grouting Reinforcement in actual mining, the failure heights of the roof and floor were reduced to 12.39 m and 4.12 m, respectively. Microseismic monitoring and water pressure loss testing verified the accuracy and applicability of this integrated technology. This study confirms the feasibility of confined mining under the conditions of dual ultra-thin aquicludes, and provides an optimized strategy for the safe and efficient extraction of coal seams under similar hydrogeological settings.

Taking the gob-side entry retaining (GER) in the 28,051 panel of Xinzhuang Coal Mine as the engineering background, this study introduces the second invariant of deviatoric stress (J₂) as a quantitative indicator of surrounding rock failure. By constructing mechanical model, performing FLAC3D numerical simulation, and conducting industrial experiment, the full-cycle failure evolution law of the surrounding rock and its control technology are systematically investigated. A mechanical model of the roadside filling body is established, from which the reasonable filling width beside the roadway is calculated to be 1.0m. Simulation results indicate that during the early stage of GER, the J₂ of the surrounding rock exhibits a ring-shaped non-uniform distribution with peak values at a depth of 2.5m in both the roof and the solid coal rib. In the middle stage, under strong mining disturbance, the J₂ peak shifts deeper to 4.5m in the roof and 3.5m in the coal rib. In the late stage, as the delayed working face distance increases, the peak value of J₂ show an increasing trend with gradually diminishing increments, stabilizing eventually. However, the peak value of J₂ at the solid coal side rib corner continues to rise. The J₂ distribution of filling body is approximately linear, with stress values increasing from the gob side to the roadway side, and the degree of stress concentration decreases with increasing delayed distance. Based on these findings, a support concept is proposed that requires anchor cables to penetrate through the J₂ peak zones of the solid coal rib and roof. This is integrated with high-density rock bolts and flexible cement slurry walls to form a comprehensive control technology for GER. Industrial practice demonstrates that the maximum roadway deformation is controlled within 294 mm, and the filling body deformation stabilizes around 90 mm, validating the effectiveness of the support design and achieving full-cycle stability control of the surrounding rock in GER.

The evaluation and judgment of surrounding rock stability after deep roadway excavation is of great significance for roadway support design and prediction of surrounding rock failure characteristics. In order to solve this problem, the advanced strain softening model based on Hoek Brown criterion developed by Itasca was used to simulate the mechanical response of surrounding rock in deep roadway. Firstly, the theoretical background and characteristics in analyzing the post peak softening characteristics of rock mass of the advanced strain softening model are introduced; Secondly, the key parameters of the model (strength parameter, modulus softening parameter, dilatancy parameter and brittle ductile plastic transition parameter) are studied. The simulation results show that the modulus softening effect and dilatancy effect of rock mass must be considered for rock mass with poor quality and strong brittleness, but not for rock mass with general quality and good quality and rock mass with less brittleness; at the same time, based on the previous analysis conclusion, with the help of analytic hierarchy process, a comprehensive index evaluation method for evaluating the stability of surrounding rock in deep roadway is proposed, which takes into account the weight differences of various factors and considers comprehensively and reasonably; Then, based on a specific engineering example, the advanced strain softening model and the conventional strain softening model (based on Hoek Brown criterion) are compared and analyzed by using the comprehensive index evaluation method. The results show that the comprehensive index conclusion obtained by the advanced strain softening model is most consistent with the field measurement results, among them, the deviation of the conventional strain softening model is 161.74%, indicating poor reliability; The IMASS model has a deviation of 26.49% and high reliability. It further shows that the advanced strain softening model based on Hoek Brown criterion is more suitable for the study of the stability characteristics of surrounding rock in deep roadway. The comprehensive index evaluation method proposed by AHP has guiding significance for the stability evaluation and support design of surrounding rock in actual underground engineering. Finally, a brief summary and analysis were conducted on the shortcomings and prospects of this study.