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Shear behavior and off-fault damage of saw-cut smooth and tension-induced rough joints in granite

Journal of Rock Mechanics and Geotechnical Engineering 2024年第4期16卷 1216-1230页

作者： Fanzhen Meng Feili Wang louis ngai yuen wong Jie Song Muzi Li Chuanqing Zhang Liming Zhang College of Science Qingdao University of TechnologyQingdao266033China Department of Earth Sciences The University of Hong KongPokfulamHong KongChina State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China Cooperative Innovation Center of Engineering Construction and Safety Shandong Peninsula Blue Economic Zone Qingdao266033China

The damage of rock joints or fractures upon shear includes the surface damage occurring at the contact asperities and the damage beneath the shear surface within the host *** latter is commonly known as off-fault damage and has been much less investigated than the surface *** main contribution of this study is to compare the results of direct shear tests conducted on saw-cut planar joints and tension-induced rough granite joints under normal stresses ranging from 1 MPa to 50 *** shear-induced off-fault damages are quantified and compared with the optical microscope *** results clearly show that the planar joints slip stably under all the normal stresses except under 50 MPa,where some local fractures and regular stick-slip occur towards the end of the *** post-peak stress drop and stick-slip occur for all the rough *** residual shear strength envelopes for the rough joints and the peak shear strength envelope for the planar joints almost *** root mean square(RMS)of asperity height for the rough joints decreases while it increases for the planar joint after shear,and a larger normal stress usually leads to a more significant decrease or increase in ***,the extent of off-fault damage(or damage zone)increases with normal stress for both planar and rough joints,and it is restricted to a very thin layer with limited micro-cracks beneath the planar joint *** comparison,the thickness of the damage zone for the rough joints is about an order of magnitude larger than that of the planar joints,and the coalesced micro-cracks are generally inclined to the shear direction with acute *** findings obtained in this study contribute to a better understanding on the frictional behavior and damage characteristics of rock joints or fractures with different roughness.

关键词： Planar joint Rough joint Shear behavior Off-fault damage Micro-cracks

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Preliminary estimation of rock-fall lateral dispersion by laboratory test

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第12期15卷 3343-3351页

作者： louis ngai yuen wong Zhicheng Tang Department of Earth Sciences The University of Hong KongHong KongChina Faculty of Engineering China University of GeosciencesWuhan430074China

Lateral dispersion significantly directs the assessment of rockfall hazard and design of countermeasures. In the present study, the dependence of lateral dispersion on different controlling factors has been systematically evaluated by performing laboratory tests using three different rock block types, namely circular block, and two types of elliptical block. The three types of rock block are released onto an inclined surface with the identical initial status. Parallel, anti-parallel, and oblique impact tests set at slope angles of 22.5° and 45°are conducted to study the block-slope interaction of rockfall. Lateral dispersion of rockfall is less influenced by the block shape for the oblique impact, while the post-impact behaviors are greatly affected by the block shape. The key factors influencing the deviation of the post-impact trajectory direction are the slope angle (θ) and direction difference (Δφ). An empirical model is then developed to characterize the deviation distribution of lateral dispersion by 5th and 95th percentile values with the inclusion of the two key factors. Linear function can be used to describe the 5th percentile boundary, while hyperbolic function is good for the 95th percentile boundary, which need to be validated by field tests in the subsequent research.

关键词： Rockfall Block shape Slope angle Oblique impact Lateral dispersion

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Rock brittleness indices and their applications to different fields of rock engineering:A review

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第1期13卷 221-247页

作者： Fanzhen Meng louis ngai yuen wong Hui Zhou College of Science Qingdao University of TechnologyQingdao266033China Department of Earth Sciences The University of Hong KongPokfulamHong KongChina State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China

Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions,such as fracability,cutability,drillability and rockburst *** such,it is of high practical value to correctly evaluate rock ***,the definition and measurement method of rock brittleness have been very diverse and not yet been *** this paper,the definitions of rock brittleness are firstly reviewed,and several representative definitions of rock brittleness are identified and briefly *** development and role of rock brittleness in different fields of rock engineering are also *** brittleness indices publicly available in rock mechanics literature are compiled,and the measurement method,applicability and limitations of some indices are *** results show that(1)the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks;(2)indices developed in one field usually are not directly applicable to other fields;and(3)the term“brittleness”is sometimes misused,and many empirically-obtained brittleness indices,which lack theoretical basis,fail to truly reflect rock *** the basis of this review,three measurement methods are identified,i.e.(1)elastic deformation before fracture,(2)shape of post-peak stressestrain curves,and(3)methods based on fracture mechanics theory,which have the potential to be further refined and unified to become the standard measurement methods of rock *** is highly beneficial for the rock mechanics community to develop a robust definition of rock *** study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications,and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term.

关键词： Rock brittleness Practical applicability Hydraulic fracturing Rockburst proneness Crack propagation Fragmentation efficiency

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Influence of grain size on strength of polymineralic crystalline rock: New insights from DEM grain-based modeling

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第4期13卷 755-766页

作者： Jun Peng louis ngai yuen wong Cee Ing Teh Department of Earth Sciences The University of Hong KongHong KongChina School of Civil and Environmental Engineering Nanyang Technological UniversitySingapore Shenzhen Institute of Research and Innovation The University of Hong KongShenzhenChina

Grain size effect on rock strength is a topic of great interest in geotechnical engineering.A consensus obtained from earlier laboratory tests is that rock strength generally decreases with the increase of grain size for both silicate and carbonate rocks;however,some recent numerical results conflict with such laboratory test *** address this intriguing issue,the effect of grain size on strength of polymineralic crystalline rock with low porosity is investigated numerically using the grain-based modeling(GBM)approach in discrete element method(DEM)by interpreting micro-cracking process in response to *** agreement with some previous DEM simulation results,the simulated rock strength is found to increase with increasing grain size for both homogeneous and heterogeneous models,even when the number of assembled disks in one mineral grain *** mechanism of strength increase with increasing grain size is mainly associated with the number of assembled smooth-joint contacts along grain interfaces and the generation of grain boundary cracks in response to *** grain interfaces significantly weaken the integrity of the rock model,which is similar to effects of inherent defects in real *** the grain size increases,fewer grain interfaces are built in the model and the rock strength becomes much ***,by solely changing the mineral grain size in a model,the mechanism of grain size effect as observed in laboratory tests cannot be *** address this issue,a method of degradation of grain boundary strength parameters is used to mimic the possible mechanism of grain size *** simulated strength using the method becomes comparable with those obtained from laboratory tests when the heterogeneity in the rock is *** of grain boundary parameters with increasing grain size provides a plausible explanation for the grain size effect on rock strength.

关键词： Grain size Rock strength Grain-based modeling(GBM)approach Grain boundary Micro-cracking behavior

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A numerical test method of California bearing ratio on graded crushed rocks using particle flow modeling

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Journal of Traffic and Transportation Engineering(English Edition) 2015年第2期2卷 107-115页

作者： Yingjun Jiang louis ngai yuen wong Jiaolong Ren Key Laboratory for Special Area Highway Engineering of Ministry of Education Chang'an University School of Civil and Environmental Engineering Nanyang Technological University School of Transportation Southeast University

In order to better understand the mechanical properties of graded crushed rocks （GCRs） and to optimize the relevant design, a numerical test method based on the particle flow modeling technique PFC2D is developed for the California bearing ratio （CBR） test on GGRs. The effects of different testing conditions and micro-mechanical parameters used in the model on the CBR numerical results have been systematically studied. The reliability of the numerical technique is verified. The numerical results suggest that the influences of the loading rate and Poisson＇s ratio on the CBR numerical test results are not significant. As such, a loading rate of 1.0-3.0 mm/min, a piston diameter of 5 cm, a specimen height of 15 cm and a specimen diameter of 15 cm are adopted for the CBR numerical test. The numerical results reveal that the GBR values increase with the friction coefficient at the contact and shear modulus of the rocks, while the influence of Poisson＇s ratio on the GBR values is insignificant. The close agreement between the CBR numerical results and experimental results suggests that the numerical simulation of the CBR values is promising to help assess the mechanical properties of GGRs and to optimize the grading design. Be- sides, the numerical study can provide useful insights on the mesoscopic mechanism.

关键词： Graded crushed rocks Particle flow modeling California bearing ratio Numerical test Micro-mechanical parametersMesoscopic mechanism

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Choosing a proper loading rate for bonded-particle model of intact rock

Choosing a proper loading rate for bonded-particle model of ...

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中国科学院地质与地球物理研究所2014年度（第14届）学术年会

作者： Xiao-Ping Zhang louis ngai yuen wong Key Laboratory of Engineering Geomechanics Institute of Geology and GeophysicsChinese Academy of Sciences School of Civil and Environmental Engineering Nanyang Technological University

Bonded-particle model(BPM) is widely used to model geomaterials,in which calibration against the results from uniaxial/triaxial compressive tests,Brazilian tensile tests and shear tests have been commonly ***,since different loading rates were used,it is difficult to assess the numerical results of these studies if the effects of the loading rate are *** paper discusses the loading mechanisms associated with different loading rates in the BPM and examines the numerical outputs under these different *** results indicate that the time step is an important factor controlling the loading rate of the BPM and should be considered in addition to the velocity of the loading *** strain rate,which is usually employed to describe the loading rate in a physical test,cannot be used for the direct comparison of different numerical tests in PFC due to the time step.A proposed "step strain rate",which considers the time step,is found to be more appropriate for comparing the loading velocity on specimens of varying *** different loading rates(0.005,0.01,0.02,0.08,0.2 and 0.6m/s) are employed in uniaxial compressive tests and Brazilian tests during this *** comprehensive examinations,a maximum step strain rate of 1.1 × 10step is considered to be appropriate for quasi-static uniaxial compressive tests and Brazilian tests using the BPM.

关键词： Bonded-particle model(BPM) Rock Loading rate Step strain rate Time step

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Displacement field analysis for cracking processes in bonded-particle model

Displacement field analysis for cracking processes in bonded...

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中国科学院地质与地球物理研究所2014年度（第14届）学术年会

Bonded-particle model(BPM) is widely used to model the cracking processes in rock/rock-like ***,the discrete particles in the BPM cannot produce a continuous displacement field,which is comparable with those in physical experiments and numerical method such as the finite element *** trend lines are introduced to analyze the displacement field type of the BPM in the present *** displacement field types(DF,DFI and DFII) are defined and used in the analysis of the cracking *** study shows that the type of displacement field may evolve during the cracking *** are advised to examine the displacement field before and right after a particular crack has *** examination of the associated type of displacement field can help reveal the nature of the crack.

关键词： Bonded-particle model(BPM) Cracking processes Displacement field Displacement trend lines

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Simulation of 3D fracture propagation under I-II-III mixed-mode loading

Rock Mechanics Bulletin

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Rock Mechanics Bulletin 2023年第4期2卷 70-83页

作者： louis ngai yuen wong Xin Cui Department of Earth Sciences The University of Hong KongPokfulamHong KongChina Now at Department of Earth Atmospheric and Planetary SciencesMassachusetts Institute of TechnologyCambridgeUSA

Fracture propagation under mixed-mode loading conditions prevails in many natural geological processes and deep engineering projects,while the corresponding numerical simulation is very challenging in rock mechanics,especially in 3D *** most previous studies,the complexity of 3D fracture geometry was over-simplified,and model III loading was often not *** this study,we propose to use an efficient stress-based Sch€ollmann criterion combined with Displacement Discontinuity Method(DDM)to model 3D fracture propagation under arbitrary I+II+III mixed-mode loading conditions.A novel curve-smoothing algorithm is developed to smoothen the fracture front during propagation,which significantly enhances the model's ability in dealing with complex 3D fracture *** particular,we adopt two different solution schemes,namely staggered and monolithic,to simulate mode I fracture propagation in the case of hydraulic *** accuracy,efficiency and convergency of the two solution schemes are compared in *** research findings suggest that the degree of coupling between fracture aperture and fluid pressure in hydraulic fracturing lies somewhere between one-way and two-way,which favors the staggered solution *** further test our new model,we provide three additional numerical examples associated with 3D fracture propagation under various mixed-mode loading *** model shows excellent performance in efficiently locating the new fracture front and reliably capturing the complex 3D fracture *** study provides a generic algorithm to model high-fidelity 3D fracture propagation without simplifying fracture geometry or loading conditions,making it widely applicable to fracture-propagation-related problems.

关键词： 3D fracture propagation Mixed-mode loading Sch€ollmann criterion Curve smoothing Hydro-mechanical(HM)coupling

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Effects of the ratio of flaw size to specimen size on cracking behavior

Effects of the ratio of flaw size to specimen size on cracki...

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中国科学院地质与地球物理研究所2015年度（第15届）学术年会

作者： Xiao-Ping Zhang louis ngai yuen wong Sijing Wang Key Laboratory of Engineering Geomechanics Institute of Geology and GeophysicsChinese Academy of Sciences School of Civil and Environmental Engineering Nanyang Technological University

To investigate the size effects on the cracking behavior of flaw-containing specimens under compressive loading,rectangular parallelepiped specimens containing a single centrally located flaw are numerically loaded using the bonded-particle model(BPM).Effects of the ratio of flaw size(length)to specimen size on cracking behavior are carefully *** numerical results show that increasing the ratio of flaw size to specimen size within a reasonable range(<0.33)has no obvious effects on the first crack initiation stress,but decreases the uniaxial compressive *** specimens of a high flaw size to specimen size ratio,the newly generated cracks have longer extension length,which allows for easier crack identification as compared with that of the low ratio *** phenomena are also observed in the physical *** on the present study,recommendations are given on choosing appropriate specimen widths in the BPM *** failures of flaw-containingspecimens as well as the outward bending effect of narrow specimens are also discussed.

关键词： Size effects Ratio of flaw size to specimen size Bonded-particle model(BPM) First cracks Secondary cracks

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单轴压缩下含预制孔洞板状花岗岩试样力学响应的试验和数值研究

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岩石力学与工程学报 2011年第6期30卷 1198-1206页

作者：李地元李夕兵李春林王毅远中南大学资源与安全工程学院湖南长沙410083 新加坡南洋理工大学土木与环境工程学院新加坡639798 挪威科学技术大学地质与矿物资源工程系

利用挪威Iddefjord花岗岩试样加工制备含双侧预制方形孔洞的板状试样,并在Instron液压伺服控制试验机上开展单轴压缩试验,监测试样的应力、应变、声发射信号特征及试样破坏过程。研究发现,随着轴向应力的增大,试样在平行于孔洞竖直方向... 详细信息

利用挪威Iddefjord花岗岩试样加工制备含双侧预制方形孔洞的板状试样,并在Instron液压伺服控制试验机上开展单轴压缩试验,监测试样的应力、应变、声发射信号特征及试样破坏过程。研究发现,随着轴向应力的增大,试样在平行于孔洞竖直方向的位置相继出现劈裂裂纹并逐渐贯通,孔洞周边岩体出现块体弹射、片帮等应变型岩爆特征。试验研究表明,含孔洞花岗岩试样在单轴压缩下总是从孔洞周边的劈裂破坏开始,试样的声发射曲线比完整岩样存在更多的跳跃突变点。在此基础上,利用FLAC3D对室内试验进行数值模拟,通过线弹性模型分析含孔洞岩石材料的应力分布特性,通过应变软化莫尔-库仑准则模拟岩样的破坏过程,监测各计算时步下单元拉伸和剪切破坏特性;发现单轴压缩下含孔洞岩样的塑形破坏单元以拉伸破坏为主,拉伸破坏单元沿孔洞竖向边界贯通形成劈裂破坏面,这和室内试验观测结果是一致的。研究结果在一定程度上揭示了深部硬岩洞室开挖后,在高地应力作用下总是产生平行于洞室开挖边界面的板裂、片帮破坏现象。

关键词：岩石力学花岗岩劈裂破坏裂纹扩展声发射数值模拟

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