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Influence of aggregate size and notch depth ratio on fracture performance of steel slag pervious concrete

CONSTRUCTION AND BUILDING MATERIALS 2021年 273卷 122036-122036页

作者： Xu, Wenlei Chen, Bo Chen, Xudong Chen, Chen Hohai Univ Coll Civil & Transportat Engn Nanjing 210098 Peoples R China Hohai Univ Coll Water Conservancy & Hydropower Engn Nanjing 210098 Peoples R China

Steel slag pervious concrete (SSPC) is a promising sustainable pavement material for sponge city construction. The influence of aggregate size and notch depth ratio on fracture performance of SSPC was studied in this work. Considering two kinds of aggregate size (4-6 mm and 10-20 mm) and four kinds of notch depth ratio (0.2, 0.3, 0.4, 0.5), the three-point bending test of a rectangular beam with a single side notch was carried out, and the whole fracture process was monitored by acoustic emission. The experimental results show that the fracture behavior of SSPC has obvious boundary effect. Meanwhile, large-size aggregates can improve the fracture strength and fracture energy of SSPC, which is related to the stronger mechanical interlocking and bonding between aggregates caused by thicker slurry layer on the surface of large-size aggregates. In addition, the acoustic emission monitoring results show that the internal wave source activity and strength are higher in the fracture process of large-size aggregate specimens, and there are more shear cracks. Finally, the PFC3D numerical model established by the discrete element theory was used to simulate the fracture behavior of SSPC. The results show that the particle flow code is an effective method to study the fracture behavior of pervious concrete. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Steel slag pervious concrete Aggregate size Notch depth ratio Fracture performance Acoustic emission particle flow code

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Assessment of Ballast Flying in the National Railway Network of Ethiopia

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Engineering（科研） 2021年第7期13卷 420-429页

作者： Fikadu Mengistu Henok F. Gebregziabher Awash-Kombolcha-Haragebeya Railway Project Ethiopian Railways Corporation Addis Ababa Ethiopia

One of the major problems in ballasted railroads is ballast flying, which is the projection of ballast particles from the at-rest position as the train passes over the track of a railway structure, mainly due to high speed. In this research, the possibility of railway ballast flying for the double track Addis-Adama section of the new Addis-Djibouti railway line is assessed by determining the major causes of ballast flying and applying Discrete Element Modeling (DEM) with the aid of particle flow code (PFC3D) software. The analysis comprised of an impact load and ballast material behavior which were used to determine the vibrational speed of individual ballast particles. The governing result from the series of discrete element analyses performed by considering fouled ballast gradation with grain-size diameter of 22.4 mm gives rise to a ballast maximum vibrational speed of 0.014 m/s. Since the ballast vibrational speed for Addis Ababa-Adama line is less than 0.02 m/s that is recommended by the literature, no ballast flight is expected under the present traffic and ballast conditions.

关键词： Railway Track Ballast Flying Discrete Element Modeling Ballast Vibrational Speed particle flow code

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Numerical simulation for compressive and tensile behaviors of rock with virtual microcracks

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ARABIAN JOURNAL OF GEOSCIENCES 2021年第10期14卷 870-870页

作者： Chen, Xiao Shi, Chong Ruan, Huai-Ning Yang, Wen-Kun Hohai Univ Key Lab Minist Educ Geomech & Embankment Engn Nanjing 210098 Peoples R China Hohai Univ Inst Geotech Res Nanjing 210098 Peoples R China

The ratio of unconfined compressive strength to tensile strength (UCS/T) is a fundamental mechanical characteristics of rock materials, and the macroscopic mechanical properties of rocks under compression and tension conditions are seriously affected by microcracks. In this study, the numerical samples with three different microcrack distribution morphology (triangular mesh microcrack distribution morphology (T-MDM), Voronoi mesh microcrack distribution morphology (V-MDM), uniform microcrack distribution morphology (U-MDM)) were established based on different geometric forms. The effects of microcrack distribution morphology, microcrack density, and microcrack-matrix bond strength ratio on the mechanical properties of rocks were investigated, and the influence of various factors on the compression-tensile strength ratio was further discussed. Results showed that the rock samples with regular microcrack distribution morphology (T-MDM and V-MDM) exhibited a more reasonable compression-tensile strength ratio than those with random microcrack distribution morphology (U-MDM), and microcrack density has a significant effect on compression-tensile strength ratio under low bond strength ratio. Further, when the microcrack-matrix bond strength ratio is within the range of 0.05-0.15, the compression-tensile strength ratio of rock is basically between 10 and 30. The research results can provide reference for the construction of microstructure in numerical model and the simulation of reasonable mechanical behavior of rock.

关键词： Microcracks Compressive-tensile strength ratio Rock Discrete element method particle flow code

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A modeling study of the micro-cracking behavior of brittle crystalline rocks under uniaxial loading considering different scenarios of grain-based models

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ARABIAN JOURNAL OF GEOSCIENCES 2021年第4期14卷 248-248页

作者： Wang, Song Zhou, Jian Zhang, Luqing Han, Zhenhua Zhang, Fenxiang Chinese Acad Sci Inst Geol & Geophys Key Lab Shale Gas & Geoengn Beijing 100029 Peoples R China Univ Chinese Acad Sci Coll Earth & Planetary Sci Beijing 100049 Peoples R China Chinese Acad Sci Innovat Acad Earth Sci Beijing 100029 Peoples R China Beijing Univ Technol Key Lab Urban Secur & Disaster Engn Minist Educ Beijing 100124 Peoples R China BGI Engn Consultants Ltd Beijing 100038 Peoples R China

The grain-based model (GBM) in two-dimensional particle flow code (PFC2D) is widely used to simulate the deformation and brittle failure of crystalline rocks. However, the original GBM consisting of the parallel-bond (PB) and the smooth-joint (SJ) produces unrealistic micro-cracking processes in which excessive microcracks are distributed along the interfaces of mineral grains under uniaxial loading. To solve the problem, this research presents a discussion of the mechanical behavior of six GBMs composed of different contact models including PB, SJ, and flat-joint (FJ). After the uniaxial compressive and direct tensile tests of numerical granites, it is found that the different contact types in GBMs have a limited influence on the tensile strength (TS), elastic modulus (E), and Poisson's ratio (nu) but have a great impact on the uniaxial compressive strength (UCS) and microcrack pattern. The UCS calculated by the PB/FJ GBM is higher than the actual value. Microcrack distributions simulated by the FJ/SJ and FJ/PB GBMs show that numerous mineral grains are cut across under uniaxial loading instead of their interfaces. While the FJ/SJ and FJ/PB GBMs may well reproduce the brittle failure process of crystalline rocks, it remains to be seen whether they will be applicable to other rock mechanics issues, including triaxial compression, thermal cracking, and hydraulic fracturing.

关键词： Grain-based model particle flow code Numerical modeling Crystalline rock Micro-cracking evolution

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A power function model for simulating creep mechanical properties of salt rock

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Journal of Central South University 2020年第2期27卷 578-591页

作者： LI Huan Ngaha Tiedeu WILLIAM Jaak DAEMEN ZHOU Jun MA Chang-kun State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan 430071China School of Civil and Environmental Engineering University of Chinese Academy of SciencesBeijing 100049China School of Resources and Environmental Sciences Chongqing UniversityChongqing 400044China Mackay School of Earth Sciences and Engineering University of NevadaRenoNVUSA

In this paper,a new micro-creep model of salt rock is proposed based on a linear parallel bonded model(LPBM)using the two-dimensional particle flow code(PFC2D).The power function weakening form is assumed to describe the variation of the parallel bonded diameter(PBD)over *** comparing with the parallel-bonded stress corrosion(PSC)model,a smaller stress fluctuation and smoother creep strain−time curves can be obtained by this power function model at the same stress *** validity and adaptability of the model to simulate creep deformation of salt rock are verified through comparing the laboratory creep test curves and the Burgers model fitting *** numerical results reveal that this model can be capable of capturing the creep deformation and damage behavior from the laboratory observations.

关键词： salt rock creep damage particle flow code power function model

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Numerical analysis of triaxial creep-fatigue interaction of rock salt

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Journal of Rock Mechanics and Geotechnical Engineering 2025年

作者： Louis Ngai Yuen Wong Kai Zhao Department of Earth Sciences Faculty of Science The University of Hong Kong Hong Kong SAR China

This study investigates the creep-fatigue interaction characteristics of rock salt under triaxial conditions. Utilizing PFC 2D to conduct creep-fatigue simulation tests on rock salt under various confining pressures and stress intervals, the research systematically analyzes the triaxial stress-strain response, creep-fatigue life and interaction, crack propagation, and energy dissipation characteristics. The Burger’s and Linear Parallel Bond (LPB) models are employed to concurrently represent time-dependent and damage behavior. The results indicate that the hysteresis loops for the axial stress-strain curves of salt specimens in triaxial creep-fatigue tests are initially dense but become sparse as fracture approaches. An increase in confining pressure results in a higher number of microcracks, increased fracture strain, extended creep-fatigue life, and greater cumulative dissipated energy upon fracture. The creep-fatigue life is shorter than the pure fatigue life at each confining pressure, highlighting a detrimental interaction effect between creep damage and fatigue damage under triaxial conditions. The variation in confining pressure has a minimal impact on the creep or fatigue fraction for the salt specimens under these conditions. Fractured salt specimens under low confining pressure exhibit penetrating inclined cracks surrounded by numerous microcracks, whereas significant dilatancy is observed under high confining pressure. The findings of this study contribute to a scientifically grounded approach for designing energy storage salt caverns, with an emphasis on long-term stability. Additionally, these findings provide a valuable reference for investigating the meso-mechanical characteristics of other rock types, particularly in relation to triaxial creep-fatigue behavior.

关键词： Triaxial compression Creep-fatigue interaction Rock salt Discrete element method particle flow code

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Weibull linear parallel bond model (WLPBM) for simulating micro-mechanical characteristics of heterogeneous rocks

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ENGINEERING ANALYSIS WITH BOUNDARY ELEMENTS 2019年 108卷 82-94页

作者： Li, Huan Yang, Chunhe Ding, Xiuli William, N. T. Yin, Hongwu Zhang, Shengnan Chinese Acad Sci Inst Rock & Soil Mech State Key Lab Geomech & Geotech Engn Wuhan 430071 Hubei Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China Yangtze River Sci Res Inst Minist Water Resources Key Lab Geotech Mech & Engn Wuhan 430010 Hubei Peoples R China Chongqing Univ Sch Resources & Environm Sci Chongqing 400044 Peoples R China Sichuan Eastern China Nat Gas Transmiss Pipeline Wuhan 430020 Hubei Peoples R China

A Weibull liner parallel bond model (WLPBM) implemented into the two-dimensional particle flow code (PFC2D) is proposed to simulate the mechanical properties of heterogeneous rocks. A continuous parameter calibration strategy associated with the Hoek-Brown strength criterion is performed to determine a series of micro-contact parameters matched with the macro responses observed in laboratory experiments (e.g., uniaxial compression test, direct tension test, and the biaxial compression test). The stress-strain responses, strength characteristics as well as the failure modes under the uniaxial and biaxial compression test are modeled and discussed detailly. The simulation results indicate that the proposed WLPBM provides a promising approach for efficiently studying nonlinear mechanical behaviors, strength characteristics and the corresponding failure modes.

关键词： particle flow code Numerical modeling Weibull distribution Homogeneity index

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Effect of Foliation and Fluid Viscosity on Hydraulic Fracturing Tests in Mica Schists Investigated Using Distinct Element Modeling and Field Data

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ROCK MECHANICS AND ROCK ENGINEERING 2019年第2期52卷 555-574页

作者： Farkas, Marton Pal Yoon, Jeoung Seok Zang, Arno Zimmermann, Guenter Stephansson, Ove Lemon, Michael Danko, Gyula GFZ German Res Ctr Geosci Sect 6 2 Geothermal Energy Syst D-14473 Potsdam Germany Golder Associates Hungary Huvosvolgyi Ut 54 H-1021 Budapest Hungary Univ Potsdam Inst Earth & Environm Sci Karl Liebknecht Str 24-25 D-14476 Potsdam Germany GFZ German Res Ctr Geosci Sect 2 6 Seism Hazard & Risk Dynam D-14473 Potsdam Germany Golder Associates 6925 Century AveSuite 100 Missisouga ON L5N 7K2 Canada

Several hydraulic fracturing tests were performed in boreholes located in central Hungary in order to determine the in-situ stress for a geological site investigation. At a depth of about 540m, the observed pressure versus time curves in mica schist with low dip angle foliation shows atypical pressure versus time results. After each pressurization cycle, the fracture breakdown pressure in the first fracturing cycle is lower than the refracturing or reopening pressure in the subsequent pressurizations. It is assumed that the viscosity of the drilling mud and observed foliation of the mica schist have a significant influence on the pressure values. In order to study this problem, numerical modeling was performed using the distinct element code particle flow code, which has been proven to be a valuable tool to investigate rock engineering problems such as hydraulic fracturing. The two-dimensional version of the code applied in this study can simulate hydro-mechanically coupled fluid flow in crystalline rock with low porosity and pre-existing fractures. In this study, the effect of foliation angle and fluid viscosity on the peak pressure is tested. The atypical characteristics of the pressure behaviour are interpreted so that mud with higher viscosity penetrates the sub-horizontal foliation plane, blocks the plane of weakness and makes the partly opened fracture tight and increase the pore pressure which decreases slowly with time. We see this viscous blocking effect as one explanation for the observed increase in fracture reopening pressure in subsequent pressurization cycles.

关键词： Hydraulic fracturing Stress measurement particle flow code Hydro-mechanical coupling Microcrack Viscous blocking

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Numerical Modeling of the Relationship Between Mechanical Properties of Granite and Microparameters of the Flat-Joint Model Considering particle Size Distribution

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MATHEMATICAL GEOSCIENCES 2019年第3期51卷 319-336页

作者： Shu, Biao Liang, Ming Zhang, Shaohe Dick, Jeffrey Cent S Univ Key Lab Metallogen Predict Nonferrous Met & Geol Minist Educ Changsha Hunan Peoples R China Cent S Univ Sch Geosci & Infophys 932 South Lushan Rd Changsha 410083 Hunan Peoples R China

Deep geothermal energy is typically stored in granite reservoirs, and natural granite is highly heterogeneous because it is composed of different sizes and shapes of mineral grains. The mechanical properties of granite are significantly affected by its heterogeneity, and this may affect the fracture initiation pressure and fracture propagation direction during deep geothermal hydraulic fracturing. An extremely important aspect in examining rock heterogeneity corresponds to the relationship between its macromechanical properties and spatial arrangement of its mineral grains. In this study, a flat-joint model (FJM) in a three-dimensional particle flow code is used to examine the effect of heterogeneity [which is associated with the particle size distribution (PSD)] on the macromechanical properties of granite. Macromechanical properties of numerical models are calibrated via laboratory uniaxial compression tests and Brazilian tension tests. The results indicate that the microparameters of the FJM significantly influence rock mechanical properties, and the relationship between the microparameters and macromechanical parameters is affected by PSD.

关键词： particle flow code Flat-joint model particle size distribution Granite Geothermal energy

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Experiment and Discrete Element Modelling on Strength, Deformation and Failure Behaviour of Shale Under Brazilian Compression

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ROCK MECHANICS AND ROCK ENGINEERING 2019年第11期52卷 4339-4359页

作者： Yang, Sheng-Qi Yin, Peng-Fei Huang, Yan-Hua China Univ Min & Technol Sch Mech & Civil Engn State Key Lab Geomech & Deep Underground Engn Xuzhou 221116 Jiangsu Peoples R China

Bedding planes or layers can have a serious effect on the mechanical behaviour of shale rock. Fractures occurring along bedding planes form a fracture network in shale hydraulic fracturing;thus, the tensile strength and fracture mode are important for hydraulic fracturing design. In this research, shale disk specimens are prepared and analysed under Brazilian test conditions. During the test, a 3D digital image correlation system (DIC) is employed to capture surface deformation, and an AE sensor and strain observation system are, respectively, used to record the AE event and central strain of the shale disk during the failure process. A new inherently anisotropic model is established with a banded-particle model and smooth joint model using the particle flow code (PFC2D). The laboratory test result shows that the Brazilian tensile strength (BTS) value decreased gradually along with bedding inclination, which corresponds to a trend of the decrease of the strength over the entire interval, but it is a rather systematic decrease, approximating a linear variation. By considering the specimen after failure, three types of fracture patterns are observed: arc fracture (AF) through outside the central part, central fracture along the loading direction (LA) and mixed fracture patterns of the two. The DIC and central strain observation systems confirm that the split fractures do not always propagate along the diametrical loading direction, which means that the traditional isotropic elastic theory no longer works for layered shale. The micro-level failure behaviour and mechanism are analysed by PFC simulation. The PFC simulation reveals that the rock matrix tensile fracture and shear fracture along bedding plane are the main fracture pattern of shale disk specimens under the Brazilian test. The bedding inclination and interlayer bonding force play a very important role in the anisotropic behaviour of the shale.

关键词： Shale Brazilian test Inherent anisotropy Failure mode 3D digital image correlation system particle flow code

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