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Influence of data analysis when exploiting DFN model representation in the application of rock mass classification systems

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第6期10卷 1046-1062页

作者： Takako Miyoshi davide elmo Steve Rogers NBK Institute of Mining University of British ColumbiaVancouverCanada Golder Associates Ltd. VancouverCanada

Discrete fracture network(DFN) models have been proved to be effective tools for the characterisation of rock masses by using statistical distributions to generate realistic three-dimensional(3 D) representations of a natural fracture network. The quality of DFN modelling relies on the quality of the field data and their interpretation. In this context, advancements in remote data acquisition have now made it possible to acquire high-quality data potentially not accessible by conventional scanline and window mapping. This paper presents a comparison between aggregate and disaggregate approaches to define fracture sets, and their role with respect to the definition of key input parameters required to generate DFN models. The focal point of the discussion is the characterisation of in situ block size distribution(IBSD) using DFN methods. An application of IBSD is the assessment of rock mass quality through rock mass classification systems such as geological strength index(GSI). As DFN models are becoming an almost integral part of many geotechnical and mining engineering problems, the authors present a method whereby realistic representation of 3 D fracture networks and block size analysis are used to estimate GSI ratings, with emphasis on the limitations that exist in rock engineering design when assigning a unique GSI value to spatially variable rock masses.

关键词： Data collection Discrete fracture network(DFN) Classification system Geological strength index(GSI)

Overhanging rock slope by design:An integrated approach using rock mass strength characterisation,large-scale numerical modelling and limit equilibrium methods

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第1期10卷 72-90页

作者： Paul Schlotfeldt davide elmo Brad Panton Golder Associates Ltd. VancouverCanada NBK Institute of Mining The University of British ColumbiaVancouverCanada

Overhanging rock slopes(steeper than 90°) are typically avoided in rock engineering design, particularly where the scale of the slope exceeds the scale of fracturing present in the rock mass. This paper highlights an integrated approach of designing overhanging rock slopes where the relative dimensions of the slope exceed the scale of fracturing and the rock mass failure needs to be considered rather than kinematic release of individual blocks. The key to the method is a simplified limit equilibrium(LE) tool that was used for the support design and analysis of a multi-faceted overhanging rock slope. The overhanging slopes required complex geometries with constantly changing orientations. The overhanging rock varied in height from 30 m to 66 m. Geomechanical modelling combined with discrete fracture network(DFN)representation of the rock mass was used to validate the rock mass strength assumptions and the failure mechanism assumed in the LE model. The advantage of the simplified LE method is that buttress and support design iterations(along with sensitivity analysis of design parameters) can be completed for various cross-sections along the proposed overhanging rock sections in an efficient manner, compared to the more time-intensive, sophisticated methods that were used for the initial validation. The method described presents the development of this design tool and assumptions made for a specific overhanging rock slope design. Other locations will have different geological conditions that can control the potential behaviour of rock slopes, however, the approach presented can be applied as a general guiding design principle for overhanging rock cut slope.

关键词： Rock slopes Discrete fracture network(DFN) Rock mass strength characterisation Numerical modelling Limit equilibrium(LE) methods

New approaches to quantify progressive damage and associated dynamic rock mass blockiness

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第2期15卷 285-295页

作者： Ladan Karimi Sharif davide elmo Doug Stead NBK Institute of Mining Engineering The University of British ColumbiaVancouverCanada Department of Earth Science Simon Fraser UniversityBurnabyCanada

In the past decade, numerical modelling has been increasingly used for simulating the mechanical behaviour of naturally fractured rock masses. In this paper, we introduce new algorithms for spatial and temporal analyses of newly generated fractures and blocks using an integrated discrete fracture network (DFN)-finite-discrete element method (FDEM) (DFN-FDEM) modelling approach. A fracture line calculator and analysis technique (i.e. discrete element method (DEM) fracture analysis, DEMFA) calculates the geometrical aspects of induced fractures using a dilation criterion. The resultant two-dimensional (2D) blocks are then identified and characterised using a graph structure. Block tracking trees allow track of newly generated blocks across timesteps and to analyse progressive breakage of these blocks into smaller blocks. Fracture statistics (number and total length of initial and induced fractures) are then related to the block forming processes to investigate damage evolution. The combination of various proposed methodologies together across various stages of modelling processes provides new insights to investigate the dependency of structure's resistance on the initial fracture configuration.

关键词： Numerical modelling Spatial analysis Temporal analysis Discrete fracture network(DFN) Finite-discrete element method(FDEM)modelling Block calculations Graph structure

Modelling of blast-induced damage in tunnels using a hybrid finite-discrete numerical approach

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Journal of Rock Mechanics and Geotechnical Engineering 2014年第6期6卷 565-573页

作者： Amichai Mitelman davide elmo NBK Institute of Mining Engineering University of British ColumbiaVancouver Canada

This paper presents the application of a hybrid finite-discrete element method to study blast-induceddamage in circular tunnels. An extensive database of field tests of underground explosions above tunnelsis used for calibrating and validating the proposed numerical method; the numerical results areshown to be in good agreement with published data for large-scale physical experiments. The method isthen used to investigate the influence of rock strength properties on tunnel durability to withstand blastloads. The presented analysis considers blast damage in tunnels excavated through relatively weak（sandstone） and strong （granite） rock materials. It was found that higher rock strength will increase thetunnel resistance to the load on one hand, but decrease attenuation on the other hand. Thus, undercertain conditions, results for weak and strong rock masses are similar. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

关键词： Blast damage Tunnels Numerical analysis Finite-discrete method

Characterizing the influence of stress-induced microcracks on the laboratory strength and fracture development in brittle rocks using a finite-discrete element method-micro discrete fracture network FDEM-μDFN approach

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Journal of Rock Mechanics and Geotechnical Engineering 2015年第6期7卷 609-625页

作者： Pooya Hamdi Doug Stead davide elmo Simon Fraser University 8888 University Drive NBK Institute of Mining Engineering University of British Columbia

Heterogeneity is an inherent component of rock and may be present in different forms including mineralheterogeneity, geometrical heterogeneity, weak grain boundaries and micro-defects. Microcracks areusually observed in crystalline rocks in two forms： natural and stress-induced; the amount of stressinducedmicrocracking increases with depth and in-situ stress. Laboratory results indicate that thephysical properties of rocks such as strength, deformability, P-wave velocity and permeability areinfluenced by increase in microcrack intensity. In this study, the finite-discrete element method （FDEM）is used to model microcrack heterogeneity by introducing into a model sample sets of microcracks usingthe proposed micro discrete fracture network （mDFN） approach. The characteristics of the microcracksrequired to create mDFN models are obtained through image analyses of thin sections of Lac du Bonnetgranite adopted from published literature. A suite of two-dimensional laboratory tests including uniaxial,triaxial compression and Brazilian tests is simulated and the results are compared with laboratory *** FDEM-mDFN models indicate that micro-heterogeneity has a profound influence on both the mechanicalbehavior and resultant fracture pattern. An increase in the microcrack intensity leads to areduction in the strength of the sample and changes the character of the rock strength envelope. Spallingand axial splitting dominate the failure mode at low confinement while shear failure is the dominantfailure mode at high confinement. Numerical results from simulated compression tests show thatmicrocracking reduces the cohesive component of strength alone, and the frictional strength componentremains unaffected. Results from simulated Brazilian tests show that the tensile strength is influenced bythe presence of microcracks, with a reduction in tensile strength as microcrack intensity increases. Theimportance of microcrack heterogeneity in reproducing a bi-linear or S-shape failure

关键词： Finite-discrete element method(FDEM) Micro discrete fracture network(μDFN) Brittle fracture

Long-term mechanical behavior and characteristics of cemented tailings backfill through impact loading

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International Journal of Minerals,Metallurgy and Materials 2020年第2期27卷 140-151页

作者： Yu-ye Tan elmo davide Yu-cheng Zhou Wei-dong Song Xiang Meng Key Laboratory of High-Efficient Mining and Safety of Metal Mines(Ministry of Education of China) University of Science and Technology BeijingBeijing 100083China School of Civil and Resources Engineering University of Science and Technology BeijingBeijing 100083China Norman B.Keevil Institute of Mining Engineering Applied Science SchoolUniversity of British ColumbiaVancouverBC Canada V6T 1Z4

Cemented tailings backfill(CTB)structures are important components of underground mine *** is important to investigate the characteristics and dynamic behavior of CTB materials because they are susceptible to disturbance by dynamic loading,such as excavation and *** this study,the authors present the results of a series of Split-Hopkinson pressure bar(SHPB)single and cyclic impact loading tests on CTB specimens to investigate the long-term dynamic mechanical properties of *** stress-strain relationship,dynamic strength,and dynamic failure characteristics of CTB specimens are analyzed and discussed to provide valuable conclusions that will improve our knowledge of CTB long-term mechanical behavior and *** instance,the dynamic peak stress under cyclic impact loading is approximately twice that under single impact loading,and the CTB specimens are less prone to fracture when cyclically *** findings and conclusions can provide a new set of references for the stability analysis of CTB materials and help guide mine designers in reducing the amount of binding agents and the associated mining cost.

关键词： cyclic impact loading cemented tailings backfill dynamic mechanical properties Split–Hopkinson pressure bar dynamic peak stress

Experimental study on dynamic mechanical property of cemented tailings backfill under SHPB impact loading

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International Journal of Minerals,Metallurgy and Materials 2019年第4期26卷 404-416页

作者： Yu-ye Tan Xin Yu davide elmo Lin-hui Xu Wei-dong Song Key Laboratory of High-Efficient Mining and Safety of Metal Mines (Ministry of Education of China) University of Science and Technology Beijing School of Civil and Resources Engineering University of Science and Technology Beijing Norman B.Keevil Institute of Mining Engineering Applied Science SchoolUniversity of British Columbia

Cemented tailings backfill(CTB) have increasingly been used in recent years to improve the stability of mining stopes in deep underground mines. Deep mining processes are often associated with rock bursting and high-speed dynamic loading conditions. Therefore, it is important to investigate the characteristics and dynamic mechanical behavior of CTB. This paper presents the results of dynamic tests on CTB specimens with different cement and solid contents using a split Hopkinson pressure bar(SHPB). The results showed that some CTB specimens exhibited one to two lower stress peaks after reaching dynamic peak stress before they completely failed. The greater the cement-to-tailings ratio is, the more obvious the strain reaction. This property mainly manifested as follows. First,the dynamic peak stress increased with the increase of the cement-to-tailings ratio when the impact velocity was fixed. Second, the dynamic peak stress had a quadratic relationship with the average stress rate. Third, the cement-to-tailings ratio could enhance the increase rate of dynamic peak stress with strain rate. In addition, the dynamic strength enhancement factor K increased with the increase of strain rate, and its value was larger than that of the rock samples. The failure modes of CTB specimens under low-speed impact were tensile failure and X conjugate shear failure, where were nearly the same as those under static uniaxial and triaxial compression. The CTB specimens were crushed and broken under critical strain, a failure mode similar to that of low-strength concrete. The results of the experimental research can improve the understanding of the dynamic mechanical properties of CTB and guide the strength design of deep mining backfills.

关键词： impact loading test cemented tailings backfill dynamic mechanical properties split Hopkinson pressure bar

深部不同断面巷道分区破裂形态与围岩结构控制

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岩土工程学报 2023年第4期45卷 720-729页

作者：许磊郭帅 davide elmo 刘洪林洪紫杰肖同强河南理工大学土木工程学院河南焦作454000 河南省地下工程与灾变防控重点实验室(河南理工大学) 河南焦作454000 英属哥伦比亚大学NBK矿业工程学院温哥华V6T 1Z4 新疆大学地质与矿业工程学院新疆乌鲁木齐830046 河南理工大学能源科学与工程学院河南焦作454000

采用理论分析、现场实测、模拟分析的方法,研究了各向等压条件下等效开挖矩形、直墙半圆拱和圆形断面分区破裂形态及围岩稳定结构。结论:3个断面分区破裂形态不同,矩形断面分区破裂呈“■”状分布,直墙半圆拱断面分区破裂呈多层的“■... 详细信息

采用理论分析、现场实测、模拟分析的方法,研究了各向等压条件下等效开挖矩形、直墙半圆拱和圆形断面分区破裂形态及围岩稳定结构。结论:3个断面分区破裂形态不同,矩形断面分区破裂呈“■”状分布,直墙半圆拱断面分区破裂呈多层的“■”状分布,圆形断面分区破裂呈“花瓣”状分布;三个断面位移特征相似,位移等值线浅部呈正立的“鸡蛋壳”形,深部呈“碗”形;支承压力在主破裂面处降低,在最外层主破裂面头部集中,在破裂面之间完整岩层处升高,呈分区集中,“波谷—波峰—波谷”震荡增高的特征向外传播;理想正方形破裂面弦长有an+1=2(1/2)an(n=1,2,3,4)关系;浅部围岩分区破裂形成后,相当于深部围岩的伪开挖,3个断面均存在多层“■”形围岩承载结构。巷道稳定原理就是促进多层承载结构相互依存,共同承载。具体措施:加密、加粗、加长锚杆(索)支护结构,建立浅部与深部多层承载结构相互联系,在浅部形成稳定锚固体促进深部围岩稳定,主破裂面精准注浆修复围岩破裂面和限制主破裂面滑移。

关键词：分区破裂围岩结构深部巷道破裂形态

Strength and energy exchange of deep sandstone under high hydraulic conditions

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Journal of Central South University 2020年第10期27卷 3053-3062页

作者： LI Fei YOU Shuang JI Hong-guang elmo davide WANG Hong-tao Beijing Key Laboratory of Urban Underground Space Engineering University of Science and Technology BeijingBeijing 100083China School of Civil and Resource Engineering University of Science and Technology BeijingBeijing 100083China Institute of Mining Engineering University of British ColumbiaBC V6T 1Z4Canada

To investigate the influence of confining pressure and pore water pressure on strength characteristics,energy storage state and energy release intensity at peak failure of deep sandstone,a series of triaxial compression tests under hydraulic coupling conditions are carried *** analyzing the process of rock deformation and failure,the stress thresholds of the rock are *** change trend of total energy density,elastic energy density and dissipated energy density of deep sandstone in the pre-peak stage is obtained by the graphical integration *** comparing the dynamic energy storage level of rocks under different confining pressures,the influence of pore water pressure on the energy dissipation at stress thresholds of crack closure stress,crack initiation stress,crack damage stress and peak stress is *** on the ratio of pre-peak total energy density to post-peak total energy density,the interaction mechanism of confining pressure and pore water pressure for the rock burst proneness of deep sandstone is *** experimental results show that the peak stress of sandstone increases with the increase of confining pressure,while the existence of pore water pressure can weaken the peak stress of *** the stress stage from crack closure stress to peak stress,the dynamic energy storage level of rock presents a trend of the inverse“check mark”.Meanwhile,the larger the confining pressure,the higher the energy storage level of ***,the pore water pressure increases the degree of energy dissipation of rock and reduces the energy storage capacity of rock,and the degree of dissipation is linear with pore water *** increase of confining pressure aggravates the instability and failure of deep sandstone,while pore water pressure has the opposite *** research results will provide necessary data support for the stability analysis of rock mass excavation in sandstone stratum under high stress and high pore water pressure.

关键词： deep sandstone high hydraulic pressure mechanical characteristics energy storage rock burst proneness