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Dynamic notched semi-circle bend(NSCB) method for measuring fracture properties of rocks:Fundamentals and applications

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第5期11卷 1066-1093页

作者： Wei Yao kaiwen xia Department of Civil and Mineral Engineering University of Toronto

Rocks are increasingly used in extreme environments characterised by high loading rates and high confining *** the fracture properties of rocks under dynamic loading and confinements are critical in various rock mechanics and rock engineering *** to the transient nature of dynamic loading,the dynamic fracture tests of rocks are much more challenging than their static *** the dynamic fracture behaviour of geomaterials relies significantly on suitable and reliable dynamic fracture testing *** of such methods is the notched semi-circle bend(NSCB)test combined with the advanced split Hopkinson pressure bar(SHPB)system,which has been recommended by the International Society for Rock Mechanics and Rock Engineering(ISRM)as the standard method for the determination of dynamic fracture *** dynamic NSCB-SHPB method can provide detailed insights into dynamic fracture properties including initiation fracture toughness,fracture energy,propagation fracture toughness and fracture *** review aims to fully describe the detailed principles and state-of-the-art applications of dynamic NSCB-SHPB *** history and principles of dynamic NSCB-SHPB tests for rocks are outlined,and then the applications of dynamic NSCB-SHPB method(including the measurements of initiation and propagation fracture toughnesses and the limiting fracture velocity,the size effect and the digital image correlation(DIC)experiments)are ***,other applications of dynamic NSCB-SHPB techniques(*** thermal,moisture and anisotropy effects on the dynamic fracture properties of geomaterials,and dynamic fracture toughness of geomaterials under pre-loading and hydrostatic pressures)are presented.

关键词： Rocks Split Hopkinson pressure bar(SHPB) Notched semi-circle bend(NSCB) High loading rate Dynamic fracture

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Numerical study on tensile failures of heterogeneous rocks

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第1期12卷 50-58页

作者： Ying Xu Wei Yao kaiwen xia State Key Laboratory of Hydraulic Engineering Simulation and Safety School of Civil EngineeringTianjin UniversityTianjin300072China Department of Civil and Mineral Engineering University of TorontoOntarioM5S 1A4Canada

Many experimental results have demonstrated the apparent discrepancy of a rock material between its flexural tensile strength measured using various bending methods and its tensile strength measured using direct tension method or Brazil disc(BD)*** understand the physical mechanism for such discrepancy,numerical simulation using the realistic failure process analysis(RFPA)is carried out in this work to simulate the tensile failure of heterogeneous *** tension and semi-circular bend(SCB)tests are simulated using RFPA for rock materials with different levels of inhomogeneity,which is characterized by the homogeneity index of the Weibull distribution used in *** numerical results show that the discrepancy in the tensile strength values is caused by the inhomogeneity of the rock ***,non-local failure criterion is adopted to calculate the characteristic length of the rock materials used in the *** is shown that below a certain value of the homogeneity index,both the characteristic length and discrepancy between two types of tensile strengths of rock decrease with increase of the homogeneity index up to a critical value,at which the discrepancy disappears and the rock material is essentially homogeneous.

关键词： Tensile strength Flexural tensile strength Realistic failure process analysis(RFPA) Homogeneity index Non-local failure Characteristic length

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Dynamic mechanical behaviors of Fangshan marble

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第5期9卷 807-817页

作者： Wei Yao Taiming He kaiwen xia State Key Laboratory of Hydraulic Engineering Simulation and Safety School of Civil EngineeringTianjin University Department of Civil Engineering University of Toronto Institute of Geophysics China Earthquake Administration

Dynamic strength parameters are extensively used in mining engineering and rock ***,there are no widely accepted dynamic failure models for *** this study,the dynamic punching shear strength,uniaxial compressive strength(UCS) and tensile strength of fine-grained Fangshan marble(FM)are first measured by using a split Hopkinson pressure bar(SHPB) *** pulse-shaping technique is then implemented to maintain the dynamic force balance in SHPB *** results show that the dynamic punching shear strength,UCS and tensile strength increase with the loading rate.A recently developed dynamic Mohr-Coulomb theory is then used to interpret the testing *** this model,the angle of internal friction φ is assumed to be independent of loading rate and is obtained using the static strength *** to the dynamic Mohr-Coulomb theory,the dynamic UCS and the dynamic tensile strength are predicted from the dynamic punching shear ***,based on this dynamic theory,the dynamic UCS is predicted from the dynamic tensile *** consistency between the predicted and measured dynamic strengths demonstrates that the dynamic Mohr-Coulomb theory is applicable to FM.

关键词： Dynamic strengths Split Hopkinson pressure bar(SHPB) Dynamic Mohr-Coulomb model Fangshan marble

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Dynamic rock tensile strengths of Laurentian granite: Experimental observation and micromechanical model

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第1期9卷 116-124页

作者： kaiwen xia Wei Yao Bangbiao Wu Department of Civil Engineering University of Toronto State Key Laboratory of Hydraulic Engineering Simulation and Safety School of Civil Engineering Tianjin University

Tensile strength is an important material property for rocks. In applications where rocks are subjected to dynamic loads, the dynamic tensile strength is the controlling parameter. Similar to the study of static tensile strength, there are various methods proposed to measure the dynamic tensile strength of *** we examine dynamic tensile strength values of Laurentian granite(LG) measured from three methods: dynamic direct tension, dynamic Brazilian disc(BD) test, and dynamic semi-circular bending(SCB). We found that the dynamic tensile strength from direct tension has the lowest value, and the dynamic SCB gives the highest strength at a given loading rate. Because the dynamic direct tension measures the intrinsic rock tensile strength, it is thus necessary to reconcile the differences in strength values between the direct tension and the other two methods. We attribute the difference between the dynamic BD results and the direct tension results to the overload and internal friction in BD tests. The difference between the dynamic SCB results and the direct tension results can be understood by invoking the non-local failure theory. It is shown that, after appropriate corrections, the dynamic tensile strengths from the two other tests can be reduced to those from direct tension.

关键词： Dynamic tensile strength Brazilian disc(BD) test Semi-circular bending(SCB) Direct tension Split Hopkinson bar

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A stress-rifting origin of Grand Canyon

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Science Bulletin 2016年第6期61卷 495-504页

作者： Chunan Tang Chunyan Bao Sanzhong Li kaiwen xia Dalian University of Technology Dalian 116024 China Shaoxing University Shaoxing 312000 China Ocean University of China Qingdao 266100 China University of Toronto Toronto ON M5S 1A1 Canada

The Grand Canyon is a massive rift in the Colorado Plateau. How and when it developed has been debated for nearly 150 years. Most geologists believe the unusual landscape was primarily shaped by water *** we propose a stress-rifting model to provide an alternative explanation for the origin of Grand *** paper adopts a brittle–ductile double layer model to simulate the deformation and rifting of the plateau due to the mantle-melting-induced expansion. Our results show that the uplift induced by thermal expansion and its associated horizontal extension can cause open fractures that extend from the brittle surface to the underlying ductile layer in a top-down way. In addition, we find that episodic uplift can deepen and connect multiple fractures together to form a larger fracture network. Our findings suggest that the formation of the Grand Canyon might have been driven by plateau uplift and its associated rifting under crustal extension, wherein water erosion played only a minor role in shaping the course of the Colorado River. The new paradigm provides simpler explanations to some of the long-standing geological mysteries surrounding the canyon.

关键词： Uplift Rift Water erosion Thermal expansion Canyon

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Correction of dynamic Brazilian disc tensile strength of rocks under preloading conditions considering the overload phenomenon and invoking the Griffith criterion

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第8期15卷 1986-1996页

作者： kaiwen xia Yuchao Yu Bangbiao Wu Wei Yao State Key Laboratory of Hydraulic Engineering Simulation and Safety School of Civil EngineeringTianjin UniversityTianjin300072China Department of Civil and Mineral Engineering University of TorontoTorontoM5S 1A4Canada

Dynamic tensile failure is a common phenomenon in deep rock practices,and thus accurately evaluating the dynamic tensile responses of rocks under triaxial pressures is of great *** Brazilian disc(BD)test is the suggested method by the International Society for Rock Mechanics and Rock Engineering(ISRM)for measuring both the static and dynamic tensile strengths of rock-like ***,due to the overload phenomenon and the complex preloading conditions,the dynamic tensile strengths of rocks measured by the BD tests tend to be *** address this issue,the dynamic BD tensile strength(BTS)of Fangshan marble(FM)under different preloading conditions were measured through a triaxial split Hopkinson pressure bar(SHPB).The fracture onset in BD specimen was captured through a strain gage around the disc *** discrepancy between the traditional tensile strength(TTS,determined by the peak load P_(f) of the BD specimen)and the nominal tensile strength(NTS,obtained from the load P_(i) when the diametral fracture commences in the tested BD specimen)was applied to quantitatively evaluating the overload *** Griffith criterion was used to rectify the calculation of the tensile stress at the disc center under triaxial stress *** results demonstrate that the overload ratio(s)increases with the loading rate(σ)and decreases with the hydrostatic pressure(σ_(s)).The TTS corrected by the Griffith criterion is independent of theσ_(s)due to the overload phenomenon,while the NTS corrected by the Griffith criterion is sensitive to both the andσ.Therefore,it is essential to modify the tensile stress in dynamic confined BD tests using both the overload correction and the Griffith criterion rectification to obtain the accurate dynamic BTS of rocks.

关键词： Dynamic brazilian disc test Overload phenomenon Dynamic tensile strength Hydrostatic pressure Griffith criterion

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Dynamic ModeⅡfracture behavior of rocks under hydrostatic pressure using the short core in compression(SCC)method

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International Journal of Mining Science and Technology 2021年第5期31卷 927-937页

作者： Wei Yao Ying XuChonglang Wang kaiwen xia Mikko Hokka State Key Laboratory of Hydraulic Engineering Simulation and Safety School of Civil EngineeringTianjin UniversityTianjin 300072China State Key Laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijing 100081China Engineering Materials Science Faculty of Engineering and Natural SciencesTampere University(TAU)POB 589FI-33014 TampereFinland Department of Civil&Mineral Engineering University of TorontoTorontoON M5S 1A4Canada

The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic ModeⅡfracture toughness KⅡCof rocks under a triaxial stress ***,the method for determining the dynamic KⅡCof rocks under a triaxial stress has not been developed *** an optimal sample preparation,the short core in compression(SCC)method was designed and verified in this study to measure the dynamic KⅡCof Fangshan marble(FM)subjected to different hydrostatic pressures through a triaxial dynamic testing *** formula for calculating the dynamic KⅡCof the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary *** experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the KⅡCof FM increases as the loading *** addition,at a given loading rate the dynamic rock KⅡCis barely affected by hydrostatic *** important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.

关键词： Loading rate Finite element method ModeⅡfracture toughness Fangshan marble Hydrostatic pressure Short core in compression

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Dynamic rock tests using split Hopkinson （Kolsky） bar system - A review

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Journal of Rock Mechanics and Geotechnical Engineering 2015年第1期7卷 27-59页

作者： kaiwen xia Wei Yao Department of Civil Engineering University of Toronto

Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different from and much more challenging than their static counterparts. Dynamic tests are usually conducted using the split Hopkinson bar or Kolsl^j bar systems, which include both split Hopkinson pressure bar （SHPB） and split Hopkinson tension bar （SHTB） systems. Significant progress has been made on the quantification of various rock dynamic properties, owing to the advances in the experimental techniques of SHPB system. This review aims to fully describe and critically assess the detailed procedures and principles of tech- niques for dynamic rock tests using split Hopkinson bars. The history and principles of SHPB are outlined, followed by the key loading techniques that are useful for dynamic rock tests with SHPB （i.e. pulse shaping, momentum-trap and multi-axial loading techniques）. Various measurement techniques for rock tests in SHPB （i.e. X-ray micro computed tomography （CT）, laser gap gauge （LGG）, digital image corre- lation （DIC）, Moir~ method, caustics method, photoelastic coating method, dynamic infrared thermog- raphy） are then discussed. As the main objective of the review, various dynamic measurement techniques for rocks using SHPB are described, including dynamic rock strength measurements （i.e. dynamic compression, tension, bending and shear tests）, dynamic fracture measurements （i.e. dynamic imitation and propagation fracture toughness, dynamic fracture energy and fracture velocity）, and dy- namic techniques for studying the influences of temperature and pore water.

关键词： Rock Split Hopkinson pressure bar (SHPB) Dynamic testsRock dynamic properties Loading rate

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Effects of fracture evolution and non-Darcy flow on the thermal performance of enhanced geothermal system in 3D complex fractured rock

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International Journal of Mining Science and Technology 2024年第4期34卷 443-459页

作者： Yachen Xie Jianxing Liao Pengfei Zhao kaiwen xia Cunbao Li Department of Civil and Mineral Engineering University of TorontoToronto M5S1A4Canada College of Water Resources and Hydropower Sichuan UniversityChengdu 610225China State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsWuhan 430071China College of Civil Engineering Guizhou UniversityGuiyang 550025China Institute of Geosafety School of Engineering and TechnologyChina University of GeosciencesBeijing 100083China State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering Shenzhen UniversityShenzhen 518060China

In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal *** this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal *** further employed the model on the Habanero enhanced geothermal systems(EGS)project located in ***,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture *** shear failure is mainly concentrated in the first fracture ***,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal ***,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and *** NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.

关键词： Coupled THM model Non-Darcy flow Deformable DFN Enhanced geothermal systems

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Comparison of microwave- and thermal-assisted rock fragmentation methods at different temperatures and loading rates

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International Journal of Mining Science and Technology 2024年第6期34卷 799-819页

作者： Wei Yao Shuai Wang Bangbiao Wu Ying Xu kaiwen xia State Key Laboratory of Hydraulic Engineering Intelligent Construction and Operation School of Civil EngineeringTianjin UniversityTianjin 300072China China Railway Design Corporation Tianjin 300308China Institute of Geosafety School of Engineering and TechnologyChina University of GeosciencesBeijing 100083China

Understanding the effects of microwave irradiation and thermal treatment on the dynamic compression and fragmentation properties of rocks is essential to quantify energy consumption in rock *** this study,Fangshan granite(FG)specimens were exposed to microwave irradiation and heat *** damage of FG specimens induced by these two methods was compared using X-ray CT scanning and ultrasonic wave *** temperatures of FG after microwave irradiation and thermal treatment were effectively evaluated using a newly proposed technique.A novelty method for precisely determining the geometric features of fragments is developed to estimate the fragmentation ***,the dynamic uniaxial compressive strength(UCS),the dynamic fragmentation characteristics,and the fragmentation energy of FG after these two pretreatment methods can be reasonably *** noticeable distinction of loading rate effect on the dynamic UCS of FG between these two pretreatment methods is first observed.A relationship is established between the dynamic UCS and the damage induced by microwave irradiation and heat ***,fragmentation energy fan analysis is introduced to accurately compare the fragmentation properties of FG after two pretreatment methods in dynamic compression tests.

关键词： Fangshan granite Dynamic experiments Microwave irradiation Thermal treatment Loading rate Fragmentation

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