Abdelilah Errahali, Emmanuel Bourgeois, Thibault Badinier, Alain Le Kouby
Natural soils often exhibit clearly anisotropic mechanical properties, yet this characteristic is frequently overlooked in numerical models due to the practical challenges of determining anisotropic parameters. As a result, the influence of anisotropy remains difficult to anticipate, and engineers have limited tools to incorporate it into design procedures. However, accounting for anisotropy is essential for producing accurate predictions of ground settlements caused by tunnelling. This paper aims to enhance the understanding of cross‐anisotropy effects on the ground surface response. A parametric analysis is performed using the finite element software CESAR‐LCPC. The study shows that anisotropy in elastic properties significantly affects key parameters of surface settlement distributions, particularly the maximum settlement and the width of the settlement trough. To assist with practical evaluations, the paper provides abacuses (design charts) and analytical approximation formulas that illustrate how the maximum settlement and trough width vary with different values of the anisotropy ratios. These results offer valuable insights and practical tools for geotechnical engineers aiming to incorporate anisotropic behaviour into settlement analysis. To further assess the practical applicability of the approach, a case history from the TULIP tunnelling project was analysed. Despite the complexity of real conditions—including three‐dimensional effects, staged excavation, and multi‐layered soils—the predictions obtained with the proposed method to take into account the soil anisotropy showed good agreement with field monitoring data, confirming its potential for use in preliminary design.
{"title":"The Impact of Soil Anisotropy on Surface Settlements Induced by Tunnelling: A Revealing Parametric Study and Nomogram Development to Improve Modelling Practice","authors":"Abdelilah Errahali, Emmanuel Bourgeois, Thibault Badinier, Alain Le Kouby","doi":"10.1002/nag.70158","DOIUrl":"https://doi.org/10.1002/nag.70158","url":null,"abstract":"Natural soils often exhibit clearly anisotropic mechanical properties, yet this characteristic is frequently overlooked in numerical models due to the practical challenges of determining anisotropic parameters. As a result, the influence of anisotropy remains difficult to anticipate, and engineers have limited tools to incorporate it into design procedures. However, accounting for anisotropy is essential for producing accurate predictions of ground settlements caused by tunnelling. This paper aims to enhance the understanding of cross‐anisotropy effects on the ground surface response. A parametric analysis is performed using the finite element software CESAR‐LCPC. The study shows that anisotropy in elastic properties significantly affects key parameters of surface settlement distributions, particularly the maximum settlement and the width of the settlement trough. To assist with practical evaluations, the paper provides abacuses (design charts) and analytical approximation formulas that illustrate how the maximum settlement and trough width vary with different values of the anisotropy ratios. These results offer valuable insights and practical tools for geotechnical engineers aiming to incorporate anisotropic behaviour into settlement analysis. To further assess the practical applicability of the approach, a case history from the TULIP tunnelling project was analysed. Despite the complexity of real conditions—including three‐dimensional effects, staged excavation, and multi‐layered soils—the predictions obtained with the proposed method to take into account the soil anisotropy showed good agreement with field monitoring data, confirming its potential for use in preliminary design.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"78 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145559439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ertai Wang, Huaning Wang, Fei Song, Alfonso Rodriguez‐Dono, Mingjing Jiang
When noncircular tunnels are constructed in the time‐dependent rock mass, stress and displacement around the tunnels are time‐dependent. Furthermore, when considering the influence of seepage flow, the ground responses are more complex. In this study, hydro‐mechanical viscoelastic analytical solutions are developed for deeply noncircular tunnels constructed in saturated time‐dependent ground. In the determining procedures, analytical solutions are developed to describe the temporal and spatial distributions of stress and displacement around arbitrarily shaped tunnels, by employing the complex variable theory. These solutions are derived from both fractional‐order viscoelastic models and classical viscoelastic models through the correspondence principle, considering factors such as time‐varying pore pressure, longitudinal advancement, and non‐uniform initial stresses in the model. Finally, the detailed explicit formulations of viscoelastic analytical solutions are developed by the separation of variables in the potential function. As a verification step, a good agreement is observed between the proposed analytical solutions and numerical predictions. In the parametric investigation, the mechanism of ground responses versus time and locations is analysed. Meanwhile, sensitivity analyses are performed to investigate the effect of viscoelastic model selections on ground behaviours. It is found that the stability of the opening progressively decreases with the increase in rheological time. In summary, the proposed solutions offer an alternative and efficient approach to predict the time‐dependent ground behaviour around tunnels, taking into account the influence of seepage flow.
{"title":"Hydro‐Mechanical Viscoelastic Analytical Solutions for Deeply Noncircular Tunnels Constructed in Saturated Time‐Dependent Ground","authors":"Ertai Wang, Huaning Wang, Fei Song, Alfonso Rodriguez‐Dono, Mingjing Jiang","doi":"10.1002/nag.70164","DOIUrl":"https://doi.org/10.1002/nag.70164","url":null,"abstract":"When noncircular tunnels are constructed in the time‐dependent rock mass, stress and displacement around the tunnels are time‐dependent. Furthermore, when considering the influence of seepage flow, the ground responses are more complex. In this study, hydro‐mechanical viscoelastic analytical solutions are developed for deeply noncircular tunnels constructed in saturated time‐dependent ground. In the determining procedures, analytical solutions are developed to describe the temporal and spatial distributions of stress and displacement around arbitrarily shaped tunnels, by employing the complex variable theory. These solutions are derived from both fractional‐order viscoelastic models and classical viscoelastic models through the correspondence principle, considering factors such as time‐varying pore pressure, longitudinal advancement, and non‐uniform initial stresses in the model. Finally, the detailed explicit formulations of viscoelastic analytical solutions are developed by the separation of variables in the potential function. As a verification step, a good agreement is observed between the proposed analytical solutions and numerical predictions. In the parametric investigation, the mechanism of ground responses versus time and locations is analysed. Meanwhile, sensitivity analyses are performed to investigate the effect of viscoelastic model selections on ground behaviours. It is found that the stability of the opening progressively decreases with the increase in rheological time. In summary, the proposed solutions offer an alternative and efficient approach to predict the time‐dependent ground behaviour around tunnels, taking into account the influence of seepage flow.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"161 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145559440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xin Li, Antonin Fabbri, Henry K. K. Wong, Benoit Pardoen, Youneng Liu, Lassana Bakary Traore
Freeze‐thaw cycles can induce irreversible deformation in compacted soils in cold regions, thereby reducing their durability. This study develops a new elasto‐plastic partially frozen model ( EPPF ‐Model) within the framework of critical state soil mechanics. A Terzaghi‐like effective stress and an ice saturation degree were incorporated in the model to account for the effects of ice content on mechanical properties. Simulation results under triaxial compression at a confining pressure of 50 kPa show that the EPPF ‐Model well demonstrates the typical relationship between strength increase and rising ice content, which reveals the strength enhancement mechanism of ice contribution in compacted soils. A coupled thermo–hydro–mechanical (THM) finite element model was developed within the framework of poromechanics, in which the mechanical behaviour is governed by the EPPF ‐Model. The formulation integrates the balance equations of momentum, water mass, and heat with the physics of in‐pore water phase change. The finite element implementation was validated against a benchmark of a freezing poroelastic soil layer. Simulated results demonstrate that the THM model can reproduce the typical cyclic shrinkage and swelling deformation phases, as well as the gradual increase in net swelling during freeze‐thaw cycle tests. The proposed approach provides a reliable computational tool for predicting the freeze‐thaw behaviour of compacted soil, supporting improved design and maintenance in cold regions.
{"title":"Modelling of Freeze‐Thaw‐Induced Plastic Behaviour in Compacted Soil","authors":"Xin Li, Antonin Fabbri, Henry K. K. Wong, Benoit Pardoen, Youneng Liu, Lassana Bakary Traore","doi":"10.1002/nag.70165","DOIUrl":"https://doi.org/10.1002/nag.70165","url":null,"abstract":"Freeze‐thaw cycles can induce irreversible deformation in compacted soils in cold regions, thereby reducing their durability. This study develops a new elasto‐plastic partially frozen model ( EPPF ‐Model) within the framework of critical state soil mechanics. A Terzaghi‐like effective stress and an ice saturation degree were incorporated in the model to account for the effects of ice content on mechanical properties. Simulation results under triaxial compression at a confining pressure of 50 kPa show that the EPPF ‐Model well demonstrates the typical relationship between strength increase and rising ice content, which reveals the strength enhancement mechanism of ice contribution in compacted soils. A coupled thermo–hydro–mechanical (THM) finite element model was developed within the framework of poromechanics, in which the mechanical behaviour is governed by the EPPF ‐Model. The formulation integrates the balance equations of momentum, water mass, and heat with the physics of in‐pore water phase change. The finite element implementation was validated against a benchmark of a freezing poroelastic soil layer. Simulated results demonstrate that the THM model can reproduce the typical cyclic shrinkage and swelling deformation phases, as well as the gradual increase in net swelling during freeze‐thaw cycle tests. The proposed approach provides a reliable computational tool for predicting the freeze‐thaw behaviour of compacted soil, supporting improved design and maintenance in cold regions.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"8 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145559411","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to deeply understand the evolution mechanism of crack propagation for granite specimens with different weathering degrees, the crack evolution law during the fracture process of weathered rock is quantitatively evaluated using the analysis of rock mechanical properties and the acoustic emission characteristic parameter RA‐AF. The results indicate that the increase in weathering degree has an obvious weaken effect on the uniaxial compressive strength and elastic modulus of rock. The weathered rock failure under uniaxial compression is dominated by tensile cracks, and meanwhile, the smaller weathering degree of rock, the larger proportion of shear cracks. The average proportions of shear cracks in the strong weathered group, moderate weathered group, and weak weathered group are 10.52%, 35.66%, and 40.52%, respectively. Through the distribution of PFC 2D cracks, it is found that the amount of intergranular cracks is significantly higher than that of intragranular cracks. Both the quantitative crack evolution characteristics using the acoustic emission characteristic parameter RA‐AF and the PFC 2D numerical simulation results are consistent with the macroscopic fracture modes of weathered granite rocks. These findings hold significant implications for the stability analysis of rock mechanics engineering impacted by weathering effects.
{"title":"Quantitative Analysis of Cracking Evolution and Acoustic Emission Characteristics for Weathered Granite Under Uniaxial Compression Tests","authors":"Guangxiang Yuan, Guilin Liu, Fei Zhao, Changjun Huang, Xiaoshan Shi, Yuchen Wang, Kejun Xin, Hongjian Wang","doi":"10.1002/nag.70171","DOIUrl":"https://doi.org/10.1002/nag.70171","url":null,"abstract":"In order to deeply understand the evolution mechanism of crack propagation for granite specimens with different weathering degrees, the crack evolution law during the fracture process of weathered rock is quantitatively evaluated using the analysis of rock mechanical properties and the acoustic emission characteristic parameter RA‐AF. The results indicate that the increase in weathering degree has an obvious weaken effect on the uniaxial compressive strength and elastic modulus of rock. The weathered rock failure under uniaxial compression is dominated by tensile cracks, and meanwhile, the smaller weathering degree of rock, the larger proportion of shear cracks. The average proportions of shear cracks in the strong weathered group, moderate weathered group, and weak weathered group are 10.52%, 35.66%, and 40.52%, respectively. Through the distribution of PFC <jats:sup>2D</jats:sup> cracks, it is found that the amount of intergranular cracks is significantly higher than that of intragranular cracks. Both the quantitative crack evolution characteristics using the acoustic emission characteristic parameter RA‐AF and the PFC <jats:sup>2D</jats:sup> numerical simulation results are consistent with the macroscopic fracture modes of weathered granite rocks. These findings hold significant implications for the stability analysis of rock mechanics engineering impacted by weathering effects.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"1 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145559437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Although scale effects in jointed rock masses are well studied, the rheological behavior of intact sedimentary soft rocks (ISSRs) at different scales remains unclear due to experimental challenges and complex microstructures. This study explores the scale‐dependent creep behavior of ISSR, controlled by mineral heterogeneity and anisotropy. Using numerical modeling techniques, including the grain‐based model in particle flow code (GBM‐PFC) and ball assembling method (BAM), the creep characteristics of coarse sandstone and mudstone are captured. A theoretical model considering “anisotropy effect” and “volume effect” is proposed to predict long‐term strength. Simulation results indicate that larger samples exhibit increased isotropy, delaying accelerated creep onset, facilitating uniform stress distribution, and reducing deformation under equivalent stress. Consequently, long‐term strength and elastic moduli increase with sample size, stabilizing at an REV of 10–12 m. A “soft rock hardening” phenomenon is identified, linking enhanced isotropy and uniform stress distribution to improved strength. Furthermore, the study provides insights for assessing roof water inrush mechanisms. Comparative analysis of mining cases shows that the thickness of effective aquiclude critically influences the types of mine water inrush in Ordos Basin: Thinner effective aquiclude experience accelerated creep and leads to the gradual water inrush with no preceding water level drop, intermediate thicknesses lead to rapid inrush following water level drop with quick flow attenuation, while thicker effective aquiclude either result in sustained water level drops with possible delayed inrush or stable water levels with no inrush.
{"title":"Numerical Study on the Scale Effect in the Creep Mechanical Behavior of Intact Sedimentary Soft Rocks in Ordos Basin","authors":"Mengnan Liu, Wei Qiao, Qijing Liang, Xiangsheng Meng, Peichao Feng","doi":"10.1002/nag.70156","DOIUrl":"https://doi.org/10.1002/nag.70156","url":null,"abstract":"Although scale effects in jointed rock masses are well studied, the rheological behavior of intact sedimentary soft rocks (ISSRs) at different scales remains unclear due to experimental challenges and complex microstructures. This study explores the scale‐dependent creep behavior of ISSR, controlled by mineral heterogeneity and anisotropy. Using numerical modeling techniques, including the grain‐based model in particle flow code (GBM‐PFC) and ball assembling method (BAM), the creep characteristics of coarse sandstone and mudstone are captured. A theoretical model considering “anisotropy effect” and “volume effect” is proposed to predict long‐term strength. Simulation results indicate that larger samples exhibit increased isotropy, delaying accelerated creep onset, facilitating uniform stress distribution, and reducing deformation under equivalent stress. Consequently, long‐term strength and elastic moduli increase with sample size, stabilizing at an REV of 10–12 m. A “soft rock hardening” phenomenon is identified, linking enhanced isotropy and uniform stress distribution to improved strength. Furthermore, the study provides insights for assessing roof water inrush mechanisms. Comparative analysis of mining cases shows that the thickness of effective aquiclude critically influences the types of mine water inrush in Ordos Basin: Thinner effective aquiclude experience accelerated creep and leads to the gradual water inrush with no preceding water level drop, intermediate thicknesses lead to rapid inrush following water level drop with quick flow attenuation, while thicker effective aquiclude either result in sustained water level drops with possible delayed inrush or stable water levels with no inrush.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"5 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145559438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Soils are inherently uncertain natural materials. In geotechnical engineering, soil properties are fundamentally characterised by testing small samples. The results will then be utilised to determine appropriate geomaterial constitutive models and associated parameters for implementation in conventional computational procedures such as finite element analysis (FEM). However, the accuracy and generalisation capability of such analyses largely depends on the selection of models, which may vary according to the specific applications. To overcome these limitations, computational approaches that do not rely on predefined soil constitutive models are emerging. In this paper, the formulation of data‐driven computing for fluid transport in porous media with particular reference to soil consolidation is derived. This does not rely on any constitutive flow law or models; instead, it directly uses the experimental data on fluid transport properties to compute fluid phase distribution during transient changes of the porous skeleton. For a discretised domain, the data‐driven solver assigns each element or quadrature point a state from an experimental dataset, satisfying mass conservation condition and fluid pressure gradient definition simultaneously. By introducing a penalty function defined by the quadratic distance between local state and material state, the problem is formulated as a constrained minimisation task solved explicitly by the Lagrange multipliers method. Subsequently, several cases were analysed using the proposed data‐driven method and compared with analytical and finite element (FE) solutions. In these tests, the data‐driven method shows good accuracy and convergence properties with further discussion on the influence of the scale and noise level of the dataset.
{"title":"Model‐Free Data‐Driven Computational Analysis for Soil Consolidation Problems","authors":"Wuzhou Zhai, Feiyang Wang, Asaad Faramarzi, Nicole Metje","doi":"10.1002/nag.70155","DOIUrl":"https://doi.org/10.1002/nag.70155","url":null,"abstract":"Soils are inherently uncertain natural materials. In geotechnical engineering, soil properties are fundamentally characterised by testing small samples. The results will then be utilised to determine appropriate geomaterial constitutive models and associated parameters for implementation in conventional computational procedures such as finite element analysis (FEM). However, the accuracy and generalisation capability of such analyses largely depends on the selection of models, which may vary according to the specific applications. To overcome these limitations, computational approaches that do not rely on predefined soil constitutive models are emerging. In this paper, the formulation of data‐driven computing for fluid transport in porous media with particular reference to soil consolidation is derived. This does not rely on any constitutive flow law or models; instead, it directly uses the experimental data on fluid transport properties to compute fluid phase distribution during transient changes of the porous skeleton. For a discretised domain, the data‐driven solver assigns each element or quadrature point a state from an experimental dataset, satisfying mass conservation condition and fluid pressure gradient definition simultaneously. By introducing a penalty function defined by the quadratic distance between local state and material state, the problem is formulated as a constrained minimisation task solved explicitly by the Lagrange multipliers method. Subsequently, several cases were analysed using the proposed data‐driven method and compared with analytical and finite element (FE) solutions. In these tests, the data‐driven method shows good accuracy and convergence properties with further discussion on the influence of the scale and noise level of the dataset.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"38 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145554294","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hongtao Li, Dong Su, Junru Zhang, Jimeng Feng, Lu Hai, Xiangsheng Chen
Layer thickness in shale arises from sedimentary variability and governs the density of weak bedding planes that act as primary pathways for fracture development. Although many studies address bedding orientation, the influence of layer thickness on mechanical behaviour and fracture mechanisms of shale remains under‐examined. This paper employs a finite‐discrete element method (FDEM) anisotropic shale model to systematically investigate how layer thickness influences shale's anisotropic mechanical and fracturing behaviours from a micro‐crack viewpoint. The results show that the sensitivity of layer thickness shows great anisotropy. The mechanical behaviours, fracture mechanism and brittleness of shale inclined at 45° and 90° are significantly affected by layer thickness, while shale with 0° inclination remains unaffected. The crack initiation stress ( CI ) threshold is independent of both layer thickness and bedding inclination, offering a robust input for future anisotropic constitutive models of layered rocks. By contrast, the crack damage stress ( CD ) threshold of shale at 45° and 90° rises with increasing thickness, indicating an earlier onset of unstable fracture growth under higher bedding densities. Furthermore, a novel brittleness index, BI C , has been proposed. It relates brittleness to the CI / CD ratio. Validation using both laboratory and numerical simulation data shows that BI C reliably evaluates shale brittleness. As BI C is derived from uniaxial compressive strength tests alone, it is more practical than conventional indices for future assessments of rock brittleness. In addition, compared with conventional brittleness indices, BI C captures the effects of shale anisotropy more effectively, showing larger and clearer differences.
{"title":"Finite‐Discrete Element Methods‐Based Analysis of Layer Thickness Effects on Mechanical Behaviour and Fracture Mechanisms in Anisotropic Shale","authors":"Hongtao Li, Dong Su, Junru Zhang, Jimeng Feng, Lu Hai, Xiangsheng Chen","doi":"10.1002/nag.70163","DOIUrl":"https://doi.org/10.1002/nag.70163","url":null,"abstract":"Layer thickness in shale arises from sedimentary variability and governs the density of weak bedding planes that act as primary pathways for fracture development. Although many studies address bedding orientation, the influence of layer thickness on mechanical behaviour and fracture mechanisms of shale remains under‐examined. This paper employs a finite‐discrete element method (FDEM) anisotropic shale model to systematically investigate how layer thickness influences shale's anisotropic mechanical and fracturing behaviours from a micro‐crack viewpoint. The results show that the sensitivity of layer thickness shows great anisotropy. The mechanical behaviours, fracture mechanism and brittleness of shale inclined at 45° and 90° are significantly affected by layer thickness, while shale with 0° inclination remains unaffected. The crack initiation stress ( <jats:italic>CI</jats:italic> ) threshold is independent of both layer thickness and bedding inclination, offering a robust input for future anisotropic constitutive models of layered rocks. By contrast, the crack damage stress ( <jats:italic>CD</jats:italic> ) threshold of shale at 45° and 90° rises with increasing thickness, indicating an earlier onset of unstable fracture growth under higher bedding densities. Furthermore, a novel brittleness index, <jats:italic> BI <jats:sub>C</jats:sub> </jats:italic> , has been proposed. It relates brittleness to the <jats:italic>CI</jats:italic> / <jats:italic>CD</jats:italic> ratio. Validation using both laboratory and numerical simulation data shows that <jats:italic> BI <jats:sub>C</jats:sub> </jats:italic> reliably evaluates shale brittleness. As <jats:italic> BI <jats:sub>C</jats:sub> </jats:italic> is derived from uniaxial compressive strength tests alone, it is more practical than conventional indices for future assessments of rock brittleness. In addition, compared with conventional brittleness indices, <jats:italic> BI <jats:sub>C</jats:sub> </jats:italic> captures the effects of shale anisotropy more effectively, showing larger and clearer differences.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"135 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145554359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ting Zhang, Xin‐Min Wang, Chang‐He Shangguan, Yi Xiang, Jian‐Zhi Zhang
Borehole pressure relief technology has increasingly become a preferred method for rockburst prevention, owing to its cost‐effectiveness and convenient construction. To analyze these mechanisms, it is essential to investigate them from multiple complementary perspectives. Unlike prior numerical studies relying solely on strength criteria, this work introduces a novel peridynamic‐based approach integrating both strength criteria and excess energy to systematically evaluate how borehole drilling parameters (borehole diameter, arrangement, and drilling sequence) influence pressure relief. The borehole pressure relief is simulated in a finite zone of 4 × 4 m 2 within deep underground rock mass. Results show that: (1) a large diameter can expand the potential damage range and improve the pressure relief efficiency; (2) the double‐row borehole arrangement exhibits superior energy dissipation capacity compared with the single‐row and triple‐flower patterns, leading to more effective strainburst risk mitigation; (3) the drilling sequence exhibits minimal influence on stress redistribution, suggesting it is not a governing parameter in pressure relief design; (4) excess energy is a necessary condition for strainburst. However, the model reveals a new insight: in deep underground rock mass, the failure strength dominates the triggering process because sufficient excess energy is already available in the high in situ stress environment. This behavior was only identifiable through the proposed dual‐criteria approach. The peridynamic model provides a reliable tool for the optimization of drilling parameters in strainburst prevention and control, and offers theoretical and practical guidance for deep underground engineering.
{"title":"Insights Into Borehole Pressure Relief Mechanism for Rockburst Prevention From a Peridynamic Investigation","authors":"Ting Zhang, Xin‐Min Wang, Chang‐He Shangguan, Yi Xiang, Jian‐Zhi Zhang","doi":"10.1002/nag.70143","DOIUrl":"https://doi.org/10.1002/nag.70143","url":null,"abstract":"Borehole pressure relief technology has increasingly become a preferred method for rockburst prevention, owing to its cost‐effectiveness and convenient construction. To analyze these mechanisms, it is essential to investigate them from multiple complementary perspectives. Unlike prior numerical studies relying solely on strength criteria, this work introduces a novel peridynamic‐based approach integrating both strength criteria and excess energy to systematically evaluate how borehole drilling parameters (borehole diameter, arrangement, and drilling sequence) influence pressure relief. The borehole pressure relief is simulated in a finite zone of 4 × 4 m <jats:sup>2</jats:sup> within deep underground rock mass. Results show that: (1) a large diameter can expand the potential damage range and improve the pressure relief efficiency; (2) the double‐row borehole arrangement exhibits superior energy dissipation capacity compared with the single‐row and triple‐flower patterns, leading to more effective strainburst risk mitigation; (3) the drilling sequence exhibits minimal influence on stress redistribution, suggesting it is not a governing parameter in pressure relief design; (4) excess energy is a necessary condition for strainburst. However, the model reveals a new insight: in deep underground rock mass, the failure strength dominates the triggering process because sufficient excess energy is already available in the high in situ stress environment. This behavior was only identifiable through the proposed dual‐criteria approach. The peridynamic model provides a reliable tool for the optimization of drilling parameters in strainburst prevention and control, and offers theoretical and practical guidance for deep underground engineering.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"5 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145554295","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tengsheng Zhang, Junhong Huang, Xinping Li, Yi Luo, Tingting Liu, Zixu Wang
To investigate the damage and failure behavior as well as crack evolution characteristics of coral reef limestone under stress‐seepage coupling, a damage constitutive model was developed for coral reef limestone subjected to coupled stress‐seepage conditions. Based on the FDEM (Finite‐Discrete Element Method), the mechanical behavior, mesoscopic progressive failure process, and crack propagation mechanisms were analyzed. The regulatory effects of confining pressure and pore water pressure on the mechanical response and seepage evolution of the coral reef limestone were also clarified. The results show that coral reef limestone exhibits pronounced brittle failure characteristics under stress‐seepage coupling. Its mechanical behavior is jointly controlled by confining pressure and seepage pressure: strength and deformation capacity increase with confining pressure but decrease with pore water pressure. The constitutive model developed using the FDEM approach can accurately describe the mechanical behavior of the rock mass under coupled stress‐seepage conditions and shows a high degree of agreement with experimental results. Confining pressure and water pressure have significant effects on the mechanical behavior and crack evolution of coral reef limestone. Under low confining and seepage pressures, cracks primarily propagate linearly in a shear‐dominated mode. As both pressures increase, the failure mode gradually transitions to a mixed tensile‐shear regime, with increased crack density and more complex propagation paths. Eventually, a multi‐branched and multi‐level through‐going failure network forms, resulting in a significant reduction in residual strength. These findings provide theoretical support for stability assessment of underground island engineering and prevention of seepage‐induced geohazards.
为了研究应力-渗流耦合作用下珊瑚礁灰岩的损伤破坏行为及裂纹演化特征，建立了应力-渗流耦合作用下珊瑚礁灰岩的损伤本构模型。基于FDEM (Finite - Discrete Element Method)，对其力学行为、细观渐进破坏过程和裂纹扩展机制进行了分析。阐明了围压和孔隙水压力对珊瑚礁灰岩力学响应和渗流演化的调节作用。结果表明：在应力-渗流耦合作用下，珊瑚礁灰岩表现出明显的脆性破坏特征。其力学行为受围压和渗流压力共同控制，强度和变形能力随围压增大而增大，随孔隙水压力增大而减小。利用FDEM方法建立的本构模型能较准确地描述岩体在应力-渗流耦合条件下的力学行为，与实验结果吻合度较高。围压和水压对珊瑚礁灰岩的力学行为和裂缝演化有显著影响。在低围压和渗流压力下，裂缝主要以剪切为主的线性扩展模式扩展。随着两种压力的增加，破坏模式逐渐转变为拉伸-剪切混合模式，裂纹密度增加，扩展路径更加复杂。最终形成多分支、多层次的贯通破坏网络，导致残余强度显著降低。研究结果为地下岛工程的稳定性评价和防渗地质灾害提供了理论支持。
{"title":"Understanding the Damage and Crack Evolution of Coral Reef Limestone Under Stress‐Seepage Coupling: Insights From the Finite‐Discrete Element Method","authors":"Tengsheng Zhang, Junhong Huang, Xinping Li, Yi Luo, Tingting Liu, Zixu Wang","doi":"10.1002/nag.70168","DOIUrl":"https://doi.org/10.1002/nag.70168","url":null,"abstract":"To investigate the damage and failure behavior as well as crack evolution characteristics of coral reef limestone under stress‐seepage coupling, a damage constitutive model was developed for coral reef limestone subjected to coupled stress‐seepage conditions. Based on the FDEM (Finite‐Discrete Element Method), the mechanical behavior, mesoscopic progressive failure process, and crack propagation mechanisms were analyzed. The regulatory effects of confining pressure and pore water pressure on the mechanical response and seepage evolution of the coral reef limestone were also clarified. The results show that coral reef limestone exhibits pronounced brittle failure characteristics under stress‐seepage coupling. Its mechanical behavior is jointly controlled by confining pressure and seepage pressure: strength and deformation capacity increase with confining pressure but decrease with pore water pressure. The constitutive model developed using the FDEM approach can accurately describe the mechanical behavior of the rock mass under coupled stress‐seepage conditions and shows a high degree of agreement with experimental results. Confining pressure and water pressure have significant effects on the mechanical behavior and crack evolution of coral reef limestone. Under low confining and seepage pressures, cracks primarily propagate linearly in a shear‐dominated mode. As both pressures increase, the failure mode gradually transitions to a mixed tensile‐shear regime, with increased crack density and more complex propagation paths. Eventually, a multi‐branched and multi‐level through‐going failure network forms, resulting in a significant reduction in residual strength. These findings provide theoretical support for stability assessment of underground island engineering and prevention of seepage‐induced geohazards.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"8 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145545668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The injection amount of CO 2 is a key parameter for the CO 2 fracturing effect of shale oil. In this paper, taking CO 2 fracturing in shale oil reservoirs as the research object, first, combining field tests and three‐dimensional well groups, the practical effects of CO 2 fracturing in shale oil reservoirs are analyzed. Second, a numerical model for CO 2 fracturing in shale oil reservoirs is established, and the effects of CO 2 consumption, soaking time on displacement efficiency, are analyzed. Third, the relationship between CO 2 intensity and cumulative oil production is compared and analyzed. Results show that: (a) Under different gas‐oil ratios, as CO 2 consumption increases, the replacement ratio also increases. (b) As the dissolved gas–oil ratio in the reservoir increases, the replacement ratio decreases under the same consumption, and the CO 2 ‐enhanced oil and reduced viscosity effect are covered by dissolved gas. (c) Under the conditions of a CO 2 consumption of 2 t/fracture and an oil–gas ratio of 0.2, after 30 days of soaking, the pressure enters the straight line segment, which is the reasonable time for soaking and the pressure to decrease in the straight line segment.
{"title":"Analysis of the Mechanism of Fracture Propagation and the Influence of Engineering Parameters on CO 2 Fracturing Effect in Shale Oil Reservoirs","authors":"Jianguang Wei, Demiao Shang, Ying Yang, Xiaofeng Zhou, Anlun Wang, Dong Zhang","doi":"10.1002/nag.70122","DOIUrl":"https://doi.org/10.1002/nag.70122","url":null,"abstract":"The injection amount of CO <jats:sub>2</jats:sub> is a key parameter for the CO <jats:sub>2</jats:sub> fracturing effect of shale oil. In this paper, taking CO <jats:sub>2</jats:sub> fracturing in shale oil reservoirs as the research object, first, combining field tests and three‐dimensional well groups, the practical effects of CO <jats:sub>2</jats:sub> fracturing in shale oil reservoirs are analyzed. Second, a numerical model for CO <jats:sub>2</jats:sub> fracturing in shale oil reservoirs is established, and the effects of CO <jats:sub>2</jats:sub> consumption, soaking time on displacement efficiency, are analyzed. Third, the relationship between CO <jats:sub>2</jats:sub> intensity and cumulative oil production is compared and analyzed. Results show that: (a) Under different gas‐oil ratios, as CO <jats:sub>2</jats:sub> consumption increases, the replacement ratio also increases. (b) As the dissolved gas–oil ratio in the reservoir increases, the replacement ratio decreases under the same consumption, and the CO <jats:sub>2</jats:sub> ‐enhanced oil and reduced viscosity effect are covered by dissolved gas. (c) Under the conditions of a CO <jats:sub>2</jats:sub> consumption of 2 t/fracture and an oil–gas ratio of 0.2, after 30 days of soaking, the pressure enters the straight line segment, which is the reasonable time for soaking and the pressure to decrease in the straight line segment.","PeriodicalId":13786,"journal":{"name":"International Journal for Numerical and Analytical Methods in Geomechanics","volume":"7 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145535698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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