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Numerical investigation into pillar failure induced by time-dependent skin degradation

International Journal of Mining Science and Technology 2017年第4期27卷 591-597页

作者： sainoki atsushi Mitri Hani S. Department of Mining and Materials Engineering McGill University Montreal H3A0E8 Canada

This paper focuses on the instability mechanism of an isolated pillar, caused by time-dependent skin degradation and strength heterogeneity. The time-dependent skin degradation is simulated with a non-linear rheological model capable of simulating tertiary creep, whereby two different pillar failure cases are investigated. The first case is of an isolated pillar in a deep hard rock underground mine and subjected to high stresses. The results show that pillar degradation is limited to the regions near the surface or the skin until two months after ore extraction. Afterwards degradation starts to extend deeper into the pillar, eventually leaving a highly-stressed pillar core due to stress transfer from the failed *** potential indices show that the risk increases exponentially at the core as time goes by. It is then demonstrated that the progressive skin degradation cannot be simulated with conventional strain-softening model assuming brittle failure. The parametric study with respect to the degree of heterogeneity reveals that heterogeneity is key to the occurrence of progressive skin degradation. The second case investigated in this study is pillar failure taking place in a very long period. Such failure becomes significantly important when assessing the risk for ground subsidence caused by pillar collapse in an abandoned mine. The analysis results demonstrate that the employed non-linear rheological model can simulate gradual skin degradation taking place over several hundred years. The percentage of damage zone volume within the pillar is merely 1% after a lapse of one days and increases to 50% after one hundred years, indicating a high risk for pillar collapse in the long term. The vertical displacements within the pillar also indicate the risk of subsidence. The proposed method is suitable for evaluating the risk of ground surface subsidence above an abandoned mine.

关键词： Pillar stability Underground mine Skin degradation Rheological model Time-dependent failure

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Quantitative analysis with plastic strain indicators to estimate damage induced by fault-slip

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

作者： atsushi sainoki Hani S.Mitri International Research Organization for Advanced Science and Technology Kumamoto University Department of Mining and Materials Engineering McGill University

In the present study, methodologies to evaluate damage around an underground opening due to seismic waves arising from mining-induced fault-slip are examined. First, expressions for an associated flow rule with a failure criterion are developed for biaxial stress conditions, which are implemented into FLAC3D code. A three-dimensional(3D) mine model encompassing a fault running parallel to a steeply dipping orebody is constructed, whereby static and dynamic analyses are performed to extract stopes and simulate fault-slip in dynamic condition, respectively. In the analysis, the developed biaxial model is applied to the stope wall. The fault-slip simulation is performed, considering shearing of fault surface asperities and resultant stress drop driving the fault-slip. Two methodologies to evaluate damage caused by seismic waves arising from the simulated fault-slip are examined:(i) the ratio of dynamic plastic strain increment to elastic strain limit and(ii) plastic strain energy density. For the former one, two types of strain increments are tested, namely effective shear strain increment and volumetric strain *** results indicate that volumetric strain increment is a suitable index for detecting damage near the stope wall, while effective shear strain increment is appropriate for evaluating damage in backfill. The evaluation method with plastic strain energy density is found to be capable of assessing damage accumulated in an extensive area caused by rock mass oscillation due to seismic wave propagation. Possible damage to mine developments in the proximity of a stope is clearly described with the index. The comparison of the two methods clarifies that the former one assesses "instantaneous" damage, which is found to be different from "accumulated" damage calculated using plastic strain energy density, in terms of damage area and its location. It is thus concluded that the combination of the two methodologies leads to more accurate damage assessment as a pr

关键词： Stability of mine opening Mining-induced fault-slip Seismic waves Biaxial stress condition

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Numerical modelling of spatially and temporally distributed on‑fault induced seismicity:implication for seismic hazards

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International Journal of Coal Science & Technology 2023年第1期10卷 108-123页

作者： atsushi sainoki Adam Karl Schwartzkopf Lishuai Jiang Hani Mitri Faculty of Advanced Science and Technology KumamotoUniversityKumamotoJapan School of Engineering The University of Western AustraliaPerthAustralia State Key Laboratory of Mining Disaster Preventionand Control Shandong University of Scienceand TechnologyShandongChina Department of Mining and Materials Engineering McGillUniversityMontrealCanada

Induced seismicity is strongly related to various engineering projects that cause anthropogenic in-situ stress change at a great ***,there is a need to estimate and mitigate the associated *** the past,various simulation methods have been developed and applied to induced seismicity analysis,but there is still a fundamental diference between simulation results and feld observations in terms of the spatial distribution of seismic events and its *** present study aims to develop a method to simulate spatially distributed on-fault seismicity whilst reproducing a complex stress state in the fault ***,an equivalent continuum model is constructed,based on a discrete fracture network within a fault damage zone,by employing the crack tensor theory.A fault core is simulated at the center of the model as a discontinuous *** the model,a heterogeneous stress state with stress anomalies in the fault zone is frst simulated by applying tractions on the model outer ***,the efective normal stress on the fault plane is decreased in a stepwise manner to induce *** simulation result is validated in terms of the b-value and other seismic source parameters,hence demonstrating that the model can reproduce spatially and temporally distributed on-fault *** analysis on the parameters shows the variation of frequency-magnitude distribution before the occurrence of large seismic *** variation is found to be consistent with feld observations,thus suggesting the potential use of this simulation method in evaluating the risk for seismic hazards in various engineering projects.

关键词： Induced seismicity Fracture network Fault damage zone Crack tensor theory

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Instantaneous stress release in fault surface asperities during mining-induced fault-slip

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Journal of Rock Mechanics and Geotechnical Engineering 2016年第5期8卷 619-628页

作者： atsushi sainoki Hani S.Mitri Department of Mining and Materials Engineering McGill University

Fault-slip taking place in underground mines occasionally causes severe damage to mine openings as a result of strong ground motion induced by seismic waves arising from fault-slip. It is indicated from previous studies that intense seismic waves could be generated with the shock unloading of fault surface asperities during fault-slip. This study investigates the shock unloading with numerical simulation. A three-dimensional （3D） numerical model with idealized asperities is constructed with the help of discrete element code 3DEC. The idealization is conducted to particularly focus on simulating the shock unloading that previous numerical models, which replicate asperity degradation and crack development during the shear behavior of a joint surface in previous studies, fail to capture and simulate. With the numerical model, static and dynamic analyses are carried out to simulate unloading of asperities in the course of fault-slip. The results obtained from the dynamic analysis show that gradual stress release takes place around the center of the asperity tip at a rate of 45 MPa/ms for the base case, while an instantaneous stress release greater than 80 MPa occurs near the periphery of the asperity tip when the contact between the upper and lower asperities is lost. The instantaneous stress release becomes more intense in the vicinity of the asperity tip, causing tensile stress more than 20 MPa. It is deduced that the tensile stress could further increase if the numerical model is discretized more densely and analysis is carried out under stress conditions at a great depth. A model parametric study shows that in-situ stress state has a significant influence on the magnitude of the generated tensile stress. The results imply that the rapid stress release generating extremely high tensile stress on the asperity tip can cause intense seismic waves when it occurs at a great depth.

关键词： Shock unloading Mining-induced fault-slip Asperity Dynamic analysis

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Influence analysis of complex crack geometric parameters on mechanical properties of soft rock

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International Journal of Coal Science & Technology 2023年第4期10卷 290-304页

作者： Yang Zhao Xin He Lishuai Jiang Zongke Wang Jianguo Ning atsushi sainoki State Key Laboratory of Mining Disaster Prevention and Control Shandong University of Science and TechnologyQingdao 266590China College of Energy and Mining Engineering Shandong University of Science and TechnologyQingdao 266590China Faculty of Advanced Science and Technology Kumamoto UniversityKumamoto 860‑8555Japan

Soft rocks, such as coal, are afected by sedimentary efects, and the surrounding rock mass of underground coal mines is generally soft and rich in joints and cracks. A clear and deep understanding of the relationship between crack geometric parameters and rock mechanics properties in cracked rock is greatly important to the design of engineering rock mass struc‑tures. In this study, computed tomography (CT) scanning was used to extract the internal crack network of coal specimens. Based on the crack size and dominant crack number, the parameters of crack area, volume, length, width, and angle were statistically analyzed by diferent sampling thresholds. In addition, the Pearson correlation coefcients between the crack parameters and uniaxial compression rock mechanics properties (uniaxial compressive strength UCS, elasticity modulus E) were calculated to quantitatively analyze the impact of each parameter. Furthermore, a method based on Pearson coefcients was used to grade the correlation between crack geometric parameters and rock mechanical properties to determine threshold values. The results indicated that the UCS and E of the specimens changed with the varied internal crack structures of the specimens, the crack parameters of area, volume, length and width all showed negative correlations with UCS and E, and the dominant crack played an important role both in weakening strength and stifness. The crack parameters of the angle are all positively correlated with the UCS and E. More crack statistics can signifcantly improve the correlation between the parameters of the crack angle and the rock mechanics properties, and the statistics of the geometric parameters of at least 16 cracks or the area larger than 5 mm2 are suggested for the analysis of complex cracked rock masses or physical reproduction using 3D printing. The results are validated and further analyzed with triaxial tests. The fndings of this study have important reference value for future research regardi

关键词： CT scanning Complex crack Sampling threshold Soft rock Rock mechanics Crack geometric parameters

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Effect of surface retaining elements on rock stability:laboratory investigation with sand powder 3D printing

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International Journal of Coal Science & Technology 2023年第4期10卷 305-324页

作者： Hao Feng Lishuai Jiang Qingwei Wang Peng Tang atsushi sainoki Hani S.Mitri State Key Laboratory of Mining Disaster Prevention and Control Shandong University of Science and TechnologyQingdao 266590China Faculty of Advanced Science and Technology Kumamoto UniversityKumamoto 860-8555Japan International Research Organization for Advanced Science and Technology Kumamoto UniversityKumamoto 860-8555Japan Department of Mining and Materials Engineering McGill UniversityMontreal H3A 0E8Canada

This study aims to investigate the benefcial efects of surface retaining elements (SREs) on the mechanical behaviors of bolted rock and roadway stability. 3D printing (3DP) technology is utilized to create rock analogue prismatic specimens for conducting this investigation. Uniaxial compression tests with acoustic emission (AE) and digital image correlation techniques have been conducted on 3DP specimens bolted with diferent SREs. The results demonstrate that the strength and modulus of elasticity of the bolted specimens show a positive correlation with the area of the SRE;the AE characteristics of the bolted specimens are higher than those of the unbolted specimen, but they decrease with an increase in SRE area, thus further improving the integrity of the bolted specimens. The reinforcement efect of SREs on the surrounding rock of roadways is further analyzed using numerical modelling and feld test. The results provide a better understanding of the role of SREs in rock bolting and the optimization of rock bolting design. Furthermore, they verify the feasibility of 3DP for rock analogues in rock mechanics tests.

关键词： Roadway stability Surface retaining element Sand-powder 3D printing Rock bolting Numerical modelling

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Integrated CO_(2)capture and reduction catalysis:Role ofγ-Al_(2)O_(3)support,unique state of potassium and synergy with copper

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Journal of Environmental Sciences 2024年第6期140卷 113-122页

作者： Donato Pinto Stefano Minorello Zhouping Zhou atsushi Urakawa Catalysis Engineering Department of Chemical EngineeringDelft University of TechnologyDelft2629HZNetherlands

Carbon dioxide capture and reduction(CCR)process emerges as an efficient catalytic strategy for CO_(2)capture and conversion to valuable chemicals.K-promoted Cu/Al_(2)O_(3)catalysts exhibited promising CO_(2)capture efficiency and highly selective conversion to syngas(CO+H_(2)).The dynamic nature of the Cu-K system at reaction conditions complicates the identification of the catalytically active phase and surface *** present work aims at more precise understanding of the roles of the potassium and copper and the contribution of the metal oxide ***γ-Al_(2)O_(3)guarantees high dispersion and destabilisation of the potassium phase,potassium and copper act synergistically to remove CO_(2)from diluted streams and promote fast regeneration of the active phase for CO_(2)capture releasing CO while passing H_(2).A temperature of 350℃is found necessary to activate H_(2)dissociation and generate the active sites for CO_(2)*** effects of synthesis parameters on the CCR activity are also described by combination of ex-situ characterisation of the materials and catalytic testing.

关键词： Carbon dioxide Carbon capture and utilisation CO_(2)capture and reduction Solid CO_(2)sorbents Heterogeneous catalysis Potassium Copper catalysts Aluminium oxide

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The mechanism of block form diversification in urban morphological transformation:Case study of grid blocks in Beijing,China

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Frontiers of Architectural Research 2024年第4期13卷 928-943页

作者： Jiankun Liu atsushi Deguchi School of Architecture Tianjin UniversityTianjin 300072China Graduate School of Frontier Science The University of TokyoChiba 277-0882Japan

Beijing is a typical traditional city in China,originating from the uniform and conventional grid plan,but transformed diversely,either on purpose or *** research took the diversification process of grid blocks as an angle to understand the transformation process of Beijing’s urban *** took 194 grid blocks within the 3rd Ring Road of Beijing as research ***,the paper proposed a whole view of Beijing’s grid blocks by 1)visualizing their construction process,2)classifying 5 morphological clusters by 7 indicators(Block size,Block shape regularity,Intensity,Coverage,Network density,Plot shape regularity,Standard deviation of plot size),and 3)investigating their ***,the diversification process of grid blocks was clarified from two layers:the block-boundary layer and the inner-space ***,the mechanism of block form diversification was clarified by exploring the connections between elements in each layer,and the influence of urban development on block form *** study re-defined the diversification process in a more quantitative way from both time and spatial *** concluded that the diversification is influenced by changes in urban planning principles and locations,and emerged thorough the long-term transformation and *** interaction between the boundary and the inner space stimulates the *** based on these,it concluded with a discussion of limitations and potentials on grid blocks’construction and renovation.

关键词： Grid block Urban morphology Diversification Morphological quantification

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Does There Exist the Applicability Limit of PDE to Describe Physical Phenomena?—A Personal Survey of Quantization, QED, Turbulence

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World Journal of Mechanics 2024年第6期14卷 97-142页

作者： atsushi Inoue Department of Mathematics Tokyo Institute of Technology Tokyo Japan

What does it mean to study PDE (Partial Differential Equation)? How and what to do “to claim proudly that I’m studying a certain PDE”? Newton mechanic uses mainly ODE (Ordinary Differential Equation) and describes nicely movements of Sun, Moon and Earth etc. Now, so-called quantum phenomenum is described by, say Schrödinger equation, PDE which explains both wave and particle characters after quantization of ODE. The coupled Maxwell-Dirac equation is also “quantized” and QED (Quantum Electro-Dynamics) theory is invented by physicists. Though it is said this QED gives very good coincidence between theoretical1 and experimental observed quantities, but what is the equation corresponding to QED? Or, is it possible to describe QED by “equation” in naive sense?

关键词： Superspace Grassmann Variables Hamilton-Jacobi Equation Quantization

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Propensity score matching analysis for clinical impact of braided-type versus laser-cut-type covered self-expandable metal stents for endoscopic ultrasound-guided hepaticogastrostomy

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Hepatobiliary & Pancreatic Diseases International 2024年第2期23卷 181-185页

作者： Mitsuki Tomita Takeshi Ogura Akitoshi Hakoda Saori Ueno atsushi Okuda Nobu Nishioka Yoshitaro Yamamoto Hiroki Nishikawa 2nd Department of Internal Medicine Osaka Medical and Pharmaceutical UniversityOsakaJapan Endoscopy Center Osaka Medical and Pharmaceutical UniversityOsakaJapan

Background:To prevent stent migration during endoscopic ultrasound-guided hepaticogastrostomy(EUS-HGS),intra-scope channel release technique is important,but is unfamiliar to non-expert *** self-expandable metal stent(SEMS)is an additional factor to prevent stent ***,no compara-tive studies of laser-cut-type and braided-type during EUS-HGS have been *** aim of this study was to compare the distance between the intrahepatic bile duct and stomach wall after EUS-HGS among laser-cut-type and braided-type ***:To evaluate stent anchoring function,we measured the distance between the hepatic parenchyma and stomach wall before EUS-HGS,one day after EUS-HGS,and 7 days after ***,propensity score matching was performed to create a propensity score for using laser-cut-type group and braided-type ***:A total of 142 patients were enrolled in this *** them,24 patients underwent EUS-HGS using a laser-cut-type SEMS,and 118 patients underwent EUS-HGS using a braided-type ***-HGS using the laser-cut-type SEMS was mainly performed by non-expert endoscopists(n=21);EUS-HGS using braided-type SEMS was mainly performed by expert endoscopists(n=98).The distance after 1 day was significantly shorter in the laser-cut-type group than that in the braided-type group[2.00(1.70-3.75)vs.6.90(3.72-11.70)mm,P<0.001].In addition,this distance remained significantly shorter in the laser-cut-type group after 7 *** these results were similar after propensity score matching analysis,the distance between hepatic parenchyma and stomach after 7 days was increased by 4 mm compared with the distance after 1 day in the braided-type *** the other hand,in the laser-cut-type group,the distance after 1 day and 7 days was almost the ***:EUS-HGS using a laser-cut-type SEMS may be safe to prevent stent migration,even in non-expert hands.

关键词： Endoscopic ultrasound-guided hepaticogastrostomy Endoscopic ultrasound-guided biliary drainage Endoscopic retrograde cholangiopancreatography

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