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GAS SCIENCE AND ENGINEERING 2024年 124卷

作者： Li, Xiaorong Yang, Henglin Wei, Yaoran Feng, Yongcun Yang, Hao Yan, Wei Fu, Li China Univ Petr Natl Key Lab Petr Resources & Engn Beijing Peoples R China China Univ Petr Coll Safety & Ocean Engn Beijing Peoples R China CNPC Engn Technol R&D Co Ltd Beijing Peoples R China China Univ Petr Coll Petr Engn Beijing Peoples R China PetroChina Zhejiang Oilfield Co Beijing Peoples R China China Univ Petr Unconvent Oil & Gas Inst Beijing Peoples R China

Wellbore instability due to natural fractures is a significant issue impeding drilling operations in shale formations. However, most of the existing literature on wellbore stability analysis focuses on the coupled effects of fluid flow and deformation, and the impact of three-dimensional natural fracture characteristics on wellbore instability is not yet closely examined. This paper carried out a series of experiments to analyze the shale sample ' s fracture characteristics and shear strength. A fully coupled 3D hydro-mechanical model was then developed using the distinct element method (DEM) to investigate the wellbore instability. Finally, a comprehensive parametric study was performed to analyze the effects of characteristics of fractures (e.g., distribution density, fracture roughness and associated shear strength, dip angle, and seepage time) on wellbore stability under different in-situ stress states. The results show that the shear strength of shale increases with the increase in normal pressure (4 MPa, 6 MPa, and 8 MPa);the shear strength increases by 64.9% when the roughness is 0.325 mm (the largest increase among the three roughness cases). The maximum displacement around the wellbore is 1.3 - 1.5 times greater under the presence of weak planes than under no weak planes. Fracture roughness poses an important impact on wellbore stability because larger fracture roughness is associated with higher fracture shear strength. As the dip angle of the weak plane increases, the number of yield zones (shear failure) and maximum wellbore displacement increases and then decreases, and the peak occurs at the dip angle of 45 degrees . The seepage time of drilling fluid is positively correlated with the number of yield zones around the wellbore, and the damage rate of drilling fluid to wellbore stability gradually decreases with the seepage time.

关键词： Wellbore instability Fractured formation Direct shear experiment distinct element method

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Insights into the application of limit equilibrium and numerical methods for predicting failure modes in a jointed rock slope

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JOURNAL OF EARTH SYSTEM SCIENCE 2025年第2期134卷 1-27页

作者： Dutta, Avishek Sarkar, Kripamoy Indian Inst Technol Indian Sch Mines Dept Appl Geol Dhanbad 826004 Jharkhand India

Road-cut slopes in the hilly terrains near the Assam-Meghalaya border in India is at a perpetual risk of the unfortunate and devastating events of landslides and rockfall hazards. Determination of the modes of failure in these vulnerable slopes forms a very significant step in the assessment of their instability. In this study, a methodology has been presented for the stability assessment of a jointed rock slope and determination of the modes of failure, using an unconventional approach of a combination of kinematic analysis and three different simulation techniques, viz., the limit equilibrium method, the finite element method, and the distinct element method. All the three predicted modes of failure from kinematic analysis have been aptly validated by the three techniques. The slope has been found to be highly susceptible to wedge and planar failures, as analyzed by the limit equilibrium method. The distinct element modelling has yielded a lower magnitude of a factor of safety against planar sliding than that yielded by the finite element modelling against flexural toppling. The slope model has been found to be highly susceptible to both wedge and planar failures. Only the finite and the distinct element methods showed the vulnerable zones in the model, yielding their corresponding displacement values. A comparative study between the finite and distinct element methods has been done to understand the differences in their algorithms and the advantages of the latter over the former with respect to the time-stepping scheme.

关键词： Modes of failure kinematic analysis limit equilibrium method finite element method distinct element method comparative study

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Seismic response of tunnel intersections in jointed rock mass within underground research laboratory: A coupled DEM-DFN approach

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JOURNAL OF EARTH SYSTEM SCIENCE 2024年第3期133卷 148页

作者： Kota, V. K. Juneja, A. Bajpai, R. K. Srivastava, P. Prabhakar, G. Indian Inst Technol Dept Civil Engn Mumbai 400 076 Maharashtra India Bhabha Atom Res Ctr Technol Dev Div NRG Mumbai 400085 India Nucl Power Corp India Ltd Mumbai Maharashtra India

The stability of tunnels in jointed rock masses can be compromised by seismic activity, making it important to understand the characteristics of waves and rock joints. This study investigates the dynamic response of two intersecting tunnels under varying input wavelength and amplitude and the influence of joint density and stiffness on their behaviour using the DEM-DFN approach. A discrete fracture network (DFN) interlay was incorporated into a distinct element method (DEM) model domain to simulate weak zones in rock masses. Analysis shows that higher fracture density reduces shear stress near the DFN interlay, while joint stiffness affects wave transmission, causing a significant drop in shear stress upon wave entry. The increase in joint density and change in interlay thickness intensified the amplification of reflected waves, resulting in wave interference and reduction in transmission waves. For tunnel intersections within the DFN interlay, the larger of the two tunnels, or the main tunnel, experienced substantial deformation when peak ground velocity (PGV) was between 0.05 and 0.25 m/s, while the smaller or access tunnel exhibited maximum displacement only when PGV exceeded this range. Amplification of waves was significant when the ratio of wavelength to tunnel diameter (lambda/D) was 10, while lambda/D > 75 produced a response similar to uniform quasi-static loading. Tunnel joints with stiffness exceeding 100 GPa/m experienced substantially lower deformations, while those with higher fracture volumetric intensity (P-32 = 2 m(2)/m(3)) led to reduced wave propagation. The size of the intersection also influenced the deformation of both tunnels, with larger intersections resulting in greater deformation.

关键词： distinct element method dynamic response harmonic load jointed rock tunnel intersection

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Numerical analysis of multi-scale mechanical theory of microfine magnesite powder molding

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GRANULAR MATTER 2024年第4期26卷 95页

作者： Zhang, Ruinan Liu, Zhaoyang Pan, Songyang Yuan, Lei Wen, Tianpeng Yu, Jingkun Northeastern Univ Sch Met Shenyang 110819 Peoples R China Northeastern Univ Key Lab Ecol Met Multimet Mineral Minist Educ Shenyang 110819 Peoples R China

This study presents a discrete element numerical model for the unidirectional compaction of microfine magnesite powder, designed to enhance the green body density based on laboratory apparatus configurations. The research demonstrated that as particle size decreased, porosity significantly reduced and density increased, resulting in a more uniform internal distribution within the green body. This led to closer particle contacts and an increased coordination number, which in turn intensified inter-particle interactions and the effectiveness of force transmission. During compaction, the distribution of force chains became more uniform, reducing localized stress concentrations and enhancing the mechanical integrity of the green body. The stress-strain relationship followed a polynomial pattern, highlighting the significant influence of particle size on the mechanical behavior during compaction. These findings provide a valuable theoretical basis for optimizing the compression molding process of microfine magnesite powder, facilitating the production of high-density, high-performance molded products.

关键词： Numerical analysis distinct element method Microfine magnesite powder Compression molding

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Seismic response of an irregular slope containing surficial weak layer and internal fractures in Dadu River, southwest China

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LANDSLIDES 2024年第3期21卷 621-640页

作者： He, Jianxian Wang, Yunsheng Zhao, Jianjun Zhang, Yingbin Wu, Junfeng Wei, Jiangtao Han, Liming Chengdu Univ Technol State Key Lab Geohazard Prevent & Geoenvironm Prot Chengdu 610059 Peoples R China Southwest Jiaotong Univ Sch Civil Engn Dept Geotech Engn Chengdu 610031 Peoples R China Jinhua Polytech Architectural Engn Inst Jinhua 322000 Peoples R China Guangxi Transportat Sci & Technol Grp CO LTD Nanning Peoples R China

Seismic site effects (topography, geology, internal fracture, et al.) and direction amplification are an important component in inducing a landslide during an earthquake. The evaluation of the dynamic response characteristics of a slope is the first and important step in earthquake engineering design and regional hazard assessment. To document the seismic response of an irregular slope, broadband seismic field monitoring seismometers were deployed along an earthquake-induced landslide Mogangling slope, on the one of important water systems in Sichuan, Dadu River. Field monitoring data reveal that ground motion is directionally amplified near 80 degrees clockwise from North parallel to slope inclination when the frequency is between 3 and 4 Hz, at the crest of the Mogangling slope. During an earthquake, the peak ground acceleration of the M1 station (slope crest) is 5.3 times greater than the M3 station (near slope toe). The standard spectral ratio (SSR) of the slope crest/slope toe (M1/M3) reaches a value of 11.5 at 1.4 Hz, during the earthquake. A series of discrete element numerical models indicate that SSR of the field monitoring data can be reproduced considering the irregular geometry, surficial weak layer, and internal fractures. The recent Luding earthquake on 5 September 2022 with a magnitude of Ms 6.8 induced slope failure in the Mogangling slope reveals the seismic amplification effect again. Our findings can offer some important insights into the mechanism of earthquake-induced landslide and regional-scale landslide distribution.

关键词： Irregular geometry Weak layer Internal fracture Topographic effect distinct element method

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Uncertainty in distinct element Modeling of Freestanding Structures Considering Stiffness Parameters

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JOURNAL OF EARTHQUAKE ENGINEERING 2024年第10期28卷 2947-2967页

作者： Saifullah, M. Khalid Wittich, Christine E. Univ Nebraska Lincoln Dept Civil & Environm Engn Lincoln NE USA Univ Nebraska Lincoln Dept Civil & Environm Engn 900 N 16th St Nebraska Hall W181 POB 880531 Lincoln NE 68588 USA

Numerical studies on freestanding structures typically leverage the distinct element method where the response is dictated by joints;however, the response carries significant uncertainty due to joint stiffness parameters. This study aims to quantify the influence of joint stiffness parameters on the global response of freestanding structures subjected to seismic excitation in a probabilistic formulation. By using a range of joint stiffness values with rectangular rigid blocks of different aspect ratios, the impact of joint stiffness parameters is evaluated against a large suite of historical ground motions. Results indicate that increasing contact stiffness results in increased stability against overturning.

关键词： Freestanding structures rocking overturning distinct element method seismic analysis fragility analysis uncertainty

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Borehole stability in naturally fractured rocks with drilling mud intrusion and associated fracture strength weakening:A coupled DFN-DEM approach

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第5期16卷 1565-1581页

作者： Yaoran Wei Yongcun Feng Zhenlai Tan Tianyu Yang Xiaorong Li Zhiyue Dai Jingen Deng College of Petroleum Engineering China University of Petroleum (Beijing)Beijing102249China State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum (Beijing)Beijing102249China College of Safety and Ocean Engineering China University of PetroleumBeijing102249China

Borehole instability in naturally fractured rocks poses significant challenges to *** mud invades the surrounding formations through natural fractures under the difference between the wellbore pressure(P w)and pore pressure(P p)during drilling,which may cause wellbore ***,the weakening of fracture strength due to mud intrusion is not considered in most existing borehole stability analyses,which may yield significant errors and misleading *** addition,only limited factors were analyzed,and the fracture distribution was *** this paper,the impacts of mud intrusion and associated fracture strength weakening on borehole stability in fractured rocks under both isotropic and anisotropic stress states are investigated using a coupled DEM(distinct element method)and DFN(discrete fracture network)*** provides estimates of the effect of fracture strength weakening,wellbore pressure,in situ stresses,and sealing efficiency on borehole *** results show that mud intrusion and weakening of fracture strength can damage the *** is demonstrated by the large displacement around the borehole,shear displacement on natural fractures,and the generation of fracture at shear *** intrusion reduces the shear strength of the fracture surface and leads to shear failure,which explains that the increase in mud weight may worsen borehole stability during overbalanced drilling in fractured formations.A higher in situ stress anisotropy exerts a significant influence on the mechanism of shear failure distribution around the ***,the effect of sealing natural fractures on maintaining borehole stability is verified in this study,and the increase in sealing efficiency reduces the radial invasion distance of drilling *** study provides a directly quantitative prediction method of borehole instability in naturally fractured formations,which can consider the discrete fracture network,mud intrusion,and as

关键词： Borehole stability Naturally fractured rocks Weakening of fracture strength Discrete fracture network distinct element method

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Numerical study on the dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs

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ENERGY EXPLORATION & EXPLOITATION 2024年第6期42卷 2331-2350页

作者： Hu, Bosheng Wu, Yongping Yu, Yang Xie, Panshi Wen, Hu Zhang, Hao Xian Univ Sci & Technol Sch Energy & Min Engn Xian 710054 Peoples R China Minist Educ China Key Lab Western Mines & Hazard Prevent Xian Peoples R China Shaanxi Ruineng Coal Ind LLC Co Yanan Peoples R China Xian Univ Sci & Technol Sch Safety Sci & Engn Xian Peoples R China

Close-hole roof-cutting technology (CHRCT, also called "dense drilling") has been widely applied in coal mines due to its economic and safety benefits. Inappropriate cutting parameters and support schemes can lead to dynamic pressure disturbances in self-forming roadways with thick and hard roofs. Moreover, fully characterizing the procedure and process of self-forming roadways using CHRCT in the field is difficult, resulting in unconvincing results. Therefore, this study aims to fill the gaps in theoretical knowledge and methodology. First, the dynamic pressure characteristics of the self-forming roadway using CHRCT were investigated, and the dynamic pressure types of the roadway were classified. There are three main types: roof cut off along the coal wall side of, severe deformation, and overhanging roof of a roadway after the second working face mining. The effects of different hole parameters (inclination angle, depth and spacing) on the roof cutting to form a roadway were also investigated. The optimal hole inclination, depth and spacing of 15 degrees, 8 m, and 200 mm were determined through a series of experiments. Then, three support schemes embedded in the roadway were compared in terms of stress evolution, bolt and cable axial forces, roof displacement, and structure. Finally, this study proposes a dynamic pressure mitigation strategy through the optimization of parameters for close-hole roof-cutting and support schemes, monitoring and controlling ground pressure in roadways, and taking auxiliary measures for pressure relief. The results show that this strategy can effectively eliminate the dynamic pressure of the roadway and meet the stability requirements of the full mining cycle. This paper presents a methodology for analysing CHRCT via numerical simulation. Moreover, this approach is of great theoretical and practical importance for dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs.

关键词： Dynamic pressure of gob-side entry distinct element method close-hole roof-cutting technology mitigation strategy support scheme

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An energy-based model with non-symmetrical branch fractures of different roughness

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BULLETIN OF ENGINEERING GEOLOGY AND THE ENVIRONMENT 2024年第8期83卷 320-320页

作者： Liu, Xin Xu, Zhenyang Guo, Lianjun Univ Sci & Technol Liaoning Sch Min Engn Anshan 114051 Peoples R China Engn & Technol Res Ctr High Efficiency Min Proc & Anshan 114051 Peoples R China Sinosteel Maanshan Gen Inst Min Res Co Ltd State Key Lab Safety & Hlth Met Mines Maanshan 243000 Peoples R China Northeastern Univ Key Lab Minist Educ Safe Min Deep Met Mines Shenyang 110819 Peoples R China Shenyang Univ Technol Sch Architecture & Civil Engn Shenyang 110870 Peoples R China

The fracture surface regarded as the three-dimensional morphological characteristics of crack propagation is formed under the impetus of energy, and its characteristics can be described by the fracture surface roughness. Investigating the fracture surface roughness is of high importance for prediction and assessment of earthquakes, calculating shear strength at the fracture zone, and comprehending fluid flow. However, an excess of available energy flowing to the crack tip would cause crack branching, and the influence of the energy on fracture surface roughness of branching is rarely considered. This paper aims to evaluate the effect of the dissipated energy on fracture surface roughness based on rock dynamic fracture experimental study of crack branching. A set of split Hopkinson pressure bar measuring systems (SHPB-PS50) for rock dynamic fracture tests was established. The morphological characteristics of crack branching on the specimen surface, the three-dimensional surface topography of the fracture surface, and the changes in the dissipated energy characteristics with the fracture surface roughness were analyzed. It is concluded that the attenuation function is suitable for expressing the relationship between the roughness parameters and the dissipated energy, and an energy model with non-symmetrical branching of different roughness is established. Additionally, a numerical simulation analytical approach is developed for building the fracture surfaces through the coordinates of the discrete fracture network to measure roughness. The numerical simulation results support the experimental conclusions. The energy-based model with non-symmetrical branch fractures of different roughness is correct.

关键词： Fracture surface roughness Dissipated energy Crack branching Split Hopkinson pressure bar distinct element method

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A new distinct element meso-model for simulating the rocking-dominated seismic response of RC columns

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EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS 2023年第3期52卷 828-838页

作者： Scattarreggia, Nicola Malomo, Daniele DeJong, Matthew J. J. Univ Sch Adv Studies IUSS Pavia Piazza Vittoria 15 I-27100 Pavia Lombardy Italy McGill Univ Dept Civil Engn 817 Sherbrooke St West Montreal PQ H3A 0C3 Canada Univ Calif Berkeley Dept Civil & Environm Engn 760 Davis Hall Berkeley CA 94720 USA Univ Sch Adv Studies IUSS Pavia Pavia Italy

The rocking-dominated seismic response of reinforced concrete (RC) columns is a complex mechanism that entails P-Delta effects, concrete crushing and spalling, rupture and dislocation of steel bars and stirrups, as well as combined localized failures causing splitting and shear-flexure cracking. In this paper, we present a new meso-scale numerical modeling strategy for the detailed simulation of the rocking response of slender RC columns under seismic actions. This work advances the current state-of-the-art by exploring the unprecedented use of the distinct element method (DEM), originally conceived for geotechnical studies and whose applicability in earthquake engineering has been primarily limited to the assessment of unreinforced masonry sub-structures. To decrease analysis time and enable the use of DEM for RC problems, concrete is herein idealized as an assembly of solid macro-block layers of size directly proportional to their distance from expected plastic hinges. These layers are connected by nonlinear interface springs to simulate tensile and shear cracking via a simplified Mohr-Coulomb criterion. Crushing of concrete in deformable blocks is modeled using the Feenstra and De Borst strain-softening linearized compression law, while confinement and combined failures are accounted for numerically through the explicit representation of longitudinal and transversal reinforcement bars, idealized as link elements. Previous experimental static and dynamic tests on full-scale RC column specimens and results from fiber-based Finite element and sectional analysis models are used to evaluate DEM results and quantify the influence of key modeling parameters, including block number and deformability, as well as the amount of damping. The agreement between simulated failure modes and force and displacement capacities and their experimental counterparts demonstrate the applicability of the proposed approach, while demonstrating the pros and cons of simplified numerical met

关键词： distinct element method reinforced concrete rocking discrete element modeling seismic analysis numerical modeling

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