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\n\n \n \n 2021\n \n \n (1)\n \n \n
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\n \n \n\n \n \n \n \n \n An enhanced tool for probing the microscopic behavior of granular materials based on X-ray micro-CT and FDEM.\n \n \n \n\n\n \n Chen, Y.; Ma, G.; Zhou, W.; Wei, D.; Zhao, Q.; Zou, Y.; and Grasselli, G.\n\n\n \n\n\n\n Computers and Geotechnics, 132. 2021.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n \n \n 7 downloads\n \n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {An enhanced tool for probing the microscopic behavior of granular materials based on X-ray micro-CT and FDEM},\n type = {article},\n year = {2021},\n keywords = {FDEM,Granular materials,Intra-particle contact force,Microscopic dynamics,Particle matching and tracking,X-ray micro-computed tomography},\n volume = {132},\n id = {0175be23-42de-3c80-9a34-451ab0e71ede},\n created = {2021-02-06T07:01:17.659Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.659Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2020 We propose an enhanced tool by combining X-ray micro-computed tomography test and hybrid finite and discrete element method to investigate the mechanical behaviors of granular materials. We first conduct a min-triaxial test of Ottawa sand under X-ray micro-CT. Then, spherical harmonic analysis is performed to characterize multi-scale morphological characteristics of particles and used in the particle matching. The particle tracking algorithm ensures the matching accuracy between particle configurations even at large strain intervals. To probe intra-particle contact force, we reconstruct the numerical sample from X-ray image data. Without calibrating material parameters, FDEM simulation quantitatively agrees with the overall response of Ottawa sand recorded in experiment. Moreover, the particle scale dynamics obtained by simulation are remarkably quantitatively consistent with experiment results. The proposed tool sheds new light on bridging length scales from particle to granular system. We find that the granular material deforms plastically through spatially localized zones of large nonaffine displacements, and the spatiotemporal evolution of these zones controls the macroscopic responses of the system. The force chain collapse is relevant to the large induced structural voids formation within the shear transformation zones. Furthermore, we discover a connection between particle stress fluctuations and particle plastic rearrangements in granular materials.},\n bibtype = {article},\n author = {Chen, Y. and Ma, G. and Zhou, W. and Wei, D. and Zhao, Q. and Zou, Y. and Grasselli, G.},\n doi = {10.1016/j.compgeo.2020.103974},\n journal = {Computers and Geotechnics}\n}\n\n © 2020 We propose an enhanced tool by combining X-ray micro-computed tomography test and hybrid finite and discrete element method to investigate the mechanical behaviors of granular materials. We first conduct a min-triaxial test of Ottawa sand under X-ray micro-CT. Then, spherical harmonic analysis is performed to characterize multi-scale morphological characteristics of particles and used in the particle matching. The particle tracking algorithm ensures the matching accuracy between particle configurations even at large strain intervals. To probe intra-particle contact force, we reconstruct the numerical sample from X-ray image data. Without calibrating material parameters, FDEM simulation quantitatively agrees with the overall response of Ottawa sand recorded in experiment. Moreover, the particle scale dynamics obtained by simulation are remarkably quantitatively consistent with experiment results. The proposed tool sheds new light on bridging length scales from particle to granular system. We find that the granular material deforms plastically through spatially localized zones of large nonaffine displacements, and the spatiotemporal evolution of these zones controls the macroscopic responses of the system. The force chain collapse is relevant to the large induced structural voids formation within the shear transformation zones. Furthermore, we discover a connection between particle stress fluctuations and particle plastic rearrangements in granular materials.\n
\n\n\n\n
\n\n \n \n 2020\n \n \n (4)\n \n \n
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\n \n \n\n \n \n \n \n \n Relocating Acoustic Emission in Rocks with Unknown Velocity Structure with Machine Learning.\n \n \n \n\n\n \n Zhao, Q.; and Glaser, S.\n\n\n \n\n\n\n Rock Mechanics and Rock Engineering, 53(5). 2020.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n \n \n 7 downloads\n \n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {Relocating Acoustic Emission in Rocks with Unknown Velocity Structure with Machine Learning},\n type = {article},\n year = {2020},\n keywords = {Acoustic emission,Artificial neural network,Machine learning,Relocation,Support vector machine,Unknown wave velocity},\n volume = {53},\n id = {ac1ec75f-788e-3e18-b9e2-6da28f74ffb8},\n created = {2021-02-06T07:01:16.989Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:16.989Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2019, Springer-Verlag GmbH Austria, part of Springer Nature. Inversion of hypocenters is the first and most fundamental step in the study of seismic activities. It requires solving the nonlinear relation between the travel time and hypocenter locations, which is heavily dependent on the knowledge of the medium properties, most importantly the velocity structure. In this study, we prove that machine learning (ML) methods including artificial neural networks (ANNs) and support vector machines (SVMs) can relocate hypocenters without a priori knowledge of the velocity structure. We train ML models with acoustic emissions (AEs) created by breaking pencil leads at known locations on a laboratory fault, using the relative P-wave arrival time as the input and AE source locations as the output. The resultant ML models can accurately relocate AEs on the fault surface. With carefully chosen training strategies, the ANN model achieved better accuracy than the SVM model. This study suggests that ML methods can provide effective and accurate approaches for relocating seismic events in a medium with unknown velocity structures.},\n bibtype = {article},\n author = {Zhao, Q. and Glaser, S.D.},\n doi = {10.1007/s00603-019-02028-8},\n journal = {Rock Mechanics and Rock Engineering},\n number = {5}\n}\n\n © 2019, Springer-Verlag GmbH Austria, part of Springer Nature. Inversion of hypocenters is the first and most fundamental step in the study of seismic activities. It requires solving the nonlinear relation between the travel time and hypocenter locations, which is heavily dependent on the knowledge of the medium properties, most importantly the velocity structure. In this study, we prove that machine learning (ML) methods including artificial neural networks (ANNs) and support vector machines (SVMs) can relocate hypocenters without a priori knowledge of the velocity structure. We train ML models with acoustic emissions (AEs) created by breaking pencil leads at known locations on a laboratory fault, using the relative P-wave arrival time as the input and AE source locations as the output. The resultant ML models can accurately relocate AEs on the fault surface. With carefully chosen training strategies, the ANN model achieved better accuracy than the SVM model. This study suggests that ML methods can provide effective and accurate approaches for relocating seismic events in a medium with unknown velocity structures.\n
\n\n\n\n \n\n \n \n \n \n \n Numerical simulation of fault slip during geothermal energy extraction.\n \n \n \n\n\n \n Zhao, Q.; Glaser, S.; Lisjak, A.; and Grasselli, G.\n\n\n \n\n\n\n In 54th U.S. Rock Mechanics/Geomechanics Symposium, 2020. \n \n\n\n\n
\n\n\n\n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
\n\n\n \n\n\n\n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
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\n\n\n@inproceedings{\n title = {Numerical simulation of fault slip during geothermal energy extraction},\n type = {inproceedings},\n year = {2020},\n id = {d7165738-d541-3070-a8dd-4043947ee1e3},\n created = {2021-02-06T07:01:17.145Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.145Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2020 ARMA, American Rock Mechanics Association Enhanced geothermal systems (EGS) have been increasingly exploited as an alternative energy source. However, unexpected induced earthquakes bring uncertainty to their wider application. We employ a 2D thermal-hydro-mechanical (THM) coupled hybrid finite-discrete element method (FDEM) to investigate fault slip induced by injecting cold water into a hot fault under geothermal conditions. We show that slip will occur on stressed fault even if the overall stress condition is in the stable regime. This slip is caused by thermal contraction that reduces the fault normal stress locally, which also cause opening of the fault. We also found that convective heat transfer coefficient, which is typically unknown for natural faults, is a controlling factor for induced fault slip. This indicates the importance of understanding fault surface geometry.},\n bibtype = {inproceedings},\n author = {Zhao, Q. and Glaser, S.D. and Lisjak, A. and Grasselli, G.},\n booktitle = {54th U.S. Rock Mechanics/Geomechanics Symposium}\n}\n\n © 2020 ARMA, American Rock Mechanics Association Enhanced geothermal systems (EGS) have been increasingly exploited as an alternative energy source. However, unexpected induced earthquakes bring uncertainty to their wider application. We employ a 2D thermal-hydro-mechanical (THM) coupled hybrid finite-discrete element method (FDEM) to investigate fault slip induced by injecting cold water into a hot fault under geothermal conditions. We show that slip will occur on stressed fault even if the overall stress condition is in the stable regime. This slip is caused by thermal contraction that reduces the fault normal stress locally, which also cause opening of the fault. We also found that convective heat transfer coefficient, which is typically unknown for natural faults, is a controlling factor for induced fault slip. This indicates the importance of understanding fault surface geometry.\n
\n\n\n\n \n\n \n \n \n \n \n Assessing Energy Budget of Laboratory Fault Slip Using Rotary Shear Experiments and Micro-Computed Tomography.\n \n \n \n\n\n \n Zhao, Q.; Glaser, S.; Tisato, N.; and Grasselli, G.\n\n\n \n\n\n\n Geophysical Research Letters, 47(1). 2020.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
\n\n\n \n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {Assessing Energy Budget of Laboratory Fault Slip Using Rotary Shear Experiments and Micro-Computed Tomography},\n type = {article},\n year = {2020},\n keywords = {energy budget,fracture energy,laboratory earthquake,machine learning,micro-CT},\n volume = {47},\n id = {d00c225f-f21c-3ec1-a7c7-ff618ba67a08},\n created = {2021-02-06T07:01:17.241Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.241Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {©2020. American Geophysical Union. All Rights Reserved. Quantitative assessment of the energy budget of earthquake events is one of the key aspects for understanding the physics of earthquakes. Investigation of laboratory fault slips under controlled conditions can provide insights on this important aspect of the natural and induced earthquakes. We conducted a rotary shear experiment under X-ray micro-computed tomography, which allowed in situ and operando measurement of macroscopic stresses and imaging of the newly formed fractures inside the sample. We estimate each component of the energy budget and found that friction energy loss (EF), fracture energy (EG), and radiated energy (ER) account for 70.16%, 15.68%, and 14.15% of the total energy budget, respectively. Quantitative analysis of the micro-computed tomography images indicates that the energy consumed by creating slip-induced off-fault fractures (EfG) accounts for only 0.3% of the total energy, less than 2% of the total EG.},\n bibtype = {article},\n author = {Zhao, Q. and Glaser, S.D. and Tisato, N. and Grasselli, G.},\n doi = {10.1029/2019GL084787},\n journal = {Geophysical Research Letters},\n number = {1}\n}\n\n ©2020. American Geophysical Union. All Rights Reserved. Quantitative assessment of the energy budget of earthquake events is one of the key aspects for understanding the physics of earthquakes. Investigation of laboratory fault slips under controlled conditions can provide insights on this important aspect of the natural and induced earthquakes. We conducted a rotary shear experiment under X-ray micro-computed tomography, which allowed in situ and operando measurement of macroscopic stresses and imaging of the newly formed fractures inside the sample. We estimate each component of the energy budget and found that friction energy loss (EF), fracture energy (EG), and radiated energy (ER) account for 70.16%, 15.68%, and 14.15% of the total energy budget, respectively. Quantitative analysis of the micro-computed tomography images indicates that the energy consumed by creating slip-induced off-fault fractures (EfG) accounts for only 0.3% of the total energy, less than 2% of the total EG.\n
\n\n\n\n \n\n \n \n \n \n \n A New Contact Formulation for Large Frictional Sliding and Its Implement in the Explicit Numerical Manifold Method.\n \n \n \n\n\n \n Wei, W.; Zhao, Q.; Jiang, Q.; and Grasselli, G.\n\n\n \n\n\n\n Rock Mechanics and Rock Engineering, 53(1). 2020.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
\n\n\n\n\n\n \n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {A New Contact Formulation for Large Frictional Sliding and Its Implement in the Explicit Numerical Manifold Method},\n type = {article},\n year = {2020},\n keywords = {Contact algorithm,Explicit method,Large frictional sliding,Numerical manifold method},\n volume = {53},\n id = {d05fa6da-178c-31ca-a73d-773455ca2fcd},\n created = {2021-02-06T07:01:17.241Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.241Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2019, Springer-Verlag GmbH Austria, part of Springer Nature. Modelling discontinuous systems involving large frictional sliding is one of the key requirements for numerical methods in geotechnical engineering. The contact algorithms for most numerical methods in geotechnical engineering is based on the judgement of contact types and the satisfaction of contact conditions by the open–close iteration, in which penalty springs between contacting bodies are added or removed repeatedly. However, the simulations involving large frictional sliding contact are not always convergent, particularly in the cases that contain a large number of contacts. To avoid the judgement of contact types and the open–close iteration, a new contact algorithm, in which the contact force is calculated directly based on the overlapped area of bodies in contact and the contact states, is proposed and implemented in the explicit numerical manifold method (NMM). Stemming from the discretization of Kuhn–Tucker conditions for contact, the equations for calculating contact force are derived and the contributions of contact force to the global iteration equation of explicit NMM are obtained. The new contact algorithm can also be implemented in other numerical methods (FEM, DEM, DDA, etc.) as well. Finally, five numerical examples are investigated to verify the proposed method and illustrate its capability.},\n bibtype = {article},\n author = {Wei, W. and Zhao, Q. and Jiang, Q. and Grasselli, G.},\n doi = {10.1007/s00603-019-01914-5},\n journal = {Rock Mechanics and Rock Engineering},\n number = {1}\n}\n\n © 2019, Springer-Verlag GmbH Austria, part of Springer Nature. Modelling discontinuous systems involving large frictional sliding is one of the key requirements for numerical methods in geotechnical engineering. The contact algorithms for most numerical methods in geotechnical engineering is based on the judgement of contact types and the satisfaction of contact conditions by the open–close iteration, in which penalty springs between contacting bodies are added or removed repeatedly. However, the simulations involving large frictional sliding contact are not always convergent, particularly in the cases that contain a large number of contacts. To avoid the judgement of contact types and the open–close iteration, a new contact algorithm, in which the contact force is calculated directly based on the overlapped area of bodies in contact and the contact states, is proposed and implemented in the explicit numerical manifold method (NMM). Stemming from the discretization of Kuhn–Tucker conditions for contact, the equations for calculating contact force are derived and the contributions of contact force to the global iteration equation of explicit NMM are obtained. The new contact algorithm can also be implemented in other numerical methods (FEM, DEM, DDA, etc.) as well. Finally, five numerical examples are investigated to verify the proposed method and illustrate its capability.\n
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\n\n \n \n 2019\n \n \n (1)\n \n \n
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\n \n \n\n \n \n \n \n \n Assessing energy budget of laboratory fault slip using quantitative micro-CT image analysis.\n \n \n \n\n\n \n Zhao, Q.; Glaser, S.; Tisato, N.; and Grasselli, G.\n\n\n \n\n\n\n In 53rd U.S. Rock Mechanics/Geomechanics Symposium, 2019. \n \n\n\n\n
\n\n\n\n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
\n\n\n\n\n\n \n\n\n\n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
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\n\n\n@inproceedings{\n title = {Assessing energy budget of laboratory fault slip using quantitative micro-CT image analysis},\n type = {inproceedings},\n year = {2019},\n id = {b8bded7a-5452-3bae-bf24-dc576ee8c8ba},\n created = {2021-02-06T07:01:17.200Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.200Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {Copyright 2019 ARMA, American Rock Mechanics Association. Off-fault fracturing that occurs out of the main fault is observed at all scales, from laboratory to plate boundaries. Understanding these co-seismic fracturing phenomena in the laboratory under controlled conditions can provide insight on the in situ dynamic stress and fault conditions of the earthquakes. Studies regarding the relative amount of energy consumed by fracturing (EG) is inconclusive, and the disagreement about the relative size of EG is related to the difficulty in assessing the fracture surface area. We conducted a rotary shear experiment under X-ray micro-CT, which allowed not only the measurement of macroscopic stresses but also the imaging of the newly formed fractures inside the sample. With the careful analysis of the micro-CT images, we quantitatively assessed the fracture surface area. Then, we used Griffith theory of brittle fracture to estimate EG, which accounted for only 0.15–0.43% of the total energy consumption during slipping. The EG we estimated may imply the lower bound of the actual fracture energy, because it did not include the micro-fractures below the resolution of the micro-CT or the energy consumed by nonelastic deformation. Friction work, which is calculated from the macroscopic shear stress and angular slipping distance, consumed most (>80%) of the total energy. Less than 18% energy may have radiated in form of stress waves.},\n bibtype = {inproceedings},\n author = {Zhao, Q. and Glaser, S.D. and Tisato, N. and Grasselli, G.},\n booktitle = {53rd U.S. Rock Mechanics/Geomechanics Symposium}\n}\n\n Copyright 2019 ARMA, American Rock Mechanics Association. Off-fault fracturing that occurs out of the main fault is observed at all scales, from laboratory to plate boundaries. Understanding these co-seismic fracturing phenomena in the laboratory under controlled conditions can provide insight on the in situ dynamic stress and fault conditions of the earthquakes. Studies regarding the relative amount of energy consumed by fracturing (EG) is inconclusive, and the disagreement about the relative size of EG is related to the difficulty in assessing the fracture surface area. We conducted a rotary shear experiment under X-ray micro-CT, which allowed not only the measurement of macroscopic stresses but also the imaging of the newly formed fractures inside the sample. With the careful analysis of the micro-CT images, we quantitatively assessed the fracture surface area. Then, we used Griffith theory of brittle fracture to estimate EG, which accounted for only 0.15–0.43% of the total energy consumption during slipping. The EG we estimated may imply the lower bound of the actual fracture energy, because it did not include the micro-fractures below the resolution of the micro-CT or the energy consumed by nonelastic deformation. Friction work, which is calculated from the macroscopic shear stress and angular slipping distance, consumed most (>80%) of the total energy. Less than 18% energy may have radiated in form of stress waves.\n
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\n\n \n \n 2018\n \n \n (7)\n \n \n
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\n \n \n\n \n \n \n \n \n Rotary shear test under X-ray micro-computed tomography.\n \n \n \n\n\n \n Zhao, Q.; Tisato, N.; and Grasselli, G.\n\n\n \n\n\n\n In 52nd U.S. Rock Mechanics/Geomechanics Symposium, 2018. \n \n\n\n\n
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\n\n\n@inproceedings{\n title = {Rotary shear test under X-ray micro-computed tomography},\n type = {inproceedings},\n year = {2018},\n id = {9ff12e23-26fd-3342-8c54-e7c574d7e6d2},\n created = {2021-02-06T07:01:17.036Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.036Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {Copyright © 2018 ARMA, American Rock Mechanics Association. We present a novel rotary shear experiment that was conducted under X-ray micro-computed tomography (µCT) scans. This combination of methodologies allows for the measurement of friction during shearing and provides the opportunity to directly observe the rock joint evolution. Our results demonstrated that the initial phase of slipping was significantly influenced by asperity interlocking and breakdown, and the asperity breakdowns created secondary fractures. We present direct observations of the real contact area with progressive wearing of the shear surface. The real contact area on the joint surface consisted of numerous contacted asperities that accounted for about 11.7–17.6% of the nominal joint surface area. The slip distance required for friction behavior to be stable was similar to the sizes of the largest contact asperities. These observations helped improve our understanding of joint slip behavior and demonstrated that the µCT technology is a powerful tool for the study of joint evolution.},\n bibtype = {inproceedings},\n author = {Zhao, Q. and Tisato, N. and Grasselli, G.},\n booktitle = {52nd U.S. Rock Mechanics/Geomechanics Symposium}\n}\n\n Copyright © 2018 ARMA, American Rock Mechanics Association. We present a novel rotary shear experiment that was conducted under X-ray micro-computed tomography (µCT) scans. This combination of methodologies allows for the measurement of friction during shearing and provides the opportunity to directly observe the rock joint evolution. Our results demonstrated that the initial phase of slipping was significantly influenced by asperity interlocking and breakdown, and the asperity breakdowns created secondary fractures. We present direct observations of the real contact area with progressive wearing of the shear surface. The real contact area on the joint surface consisted of numerous contacted asperities that accounted for about 11.7–17.6% of the nominal joint surface area. The slip distance required for friction behavior to be stable was similar to the sizes of the largest contact asperities. These observations helped improve our understanding of joint slip behavior and demonstrated that the µCT technology is a powerful tool for the study of joint evolution.\n
\n\n\n\n \n\n \n \n \n \n \n Grain based modelling of rocks using the combined finite-discrete element method.\n \n \n \n\n\n \n Abdelaziz, A.; Zhao, Q.; and Grasselli, G.\n\n\n \n\n\n\n Computers and Geotechnics, 103. 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n\n\n\n
\n\n\n \n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {Grain based modelling of rocks using the combined finite-discrete element method},\n type = {article},\n year = {2018},\n keywords = {Combined finite-discrete element method,Grain based modelling,Microscopic and macroscopic rock behaviour},\n volume = {103},\n id = {2988392d-81b5-38d6-b5b4-95941625fc88},\n created = {2021-02-06T07:01:17.039Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.039Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2018 Elsevier Ltd This paper describes the implementation and advantages of grain based modelling (GBM) in the combined finite-discrete element method (FDEM) to study the mechanical behaviour of crystalline rocks. GBM in FDEM honours grain petrological properties and explicitly models grain boundaries. The simulation results demonstrated that GBM in FDEM predicted more realistic microscopic and macroscopic response of rocks than conventional FDEM models. The explicit modelling of crack boundaries captured microscopic failure transition from along grain boundaries to coalescence along the shear band, dominated by intraphase cracks. This novel framework presents a gateway into further understanding the behaviour of crystalline rocks and granular minerals.},\n bibtype = {article},\n author = {Abdelaziz, A. and Zhao, Q. and Grasselli, G.},\n doi = {10.1016/j.compgeo.2018.07.003},\n journal = {Computers and Geotechnics}\n}\n\n © 2018 Elsevier Ltd This paper describes the implementation and advantages of grain based modelling (GBM) in the combined finite-discrete element method (FDEM) to study the mechanical behaviour of crystalline rocks. GBM in FDEM honours grain petrological properties and explicitly models grain boundaries. The simulation results demonstrated that GBM in FDEM predicted more realistic microscopic and macroscopic response of rocks than conventional FDEM models. The explicit modelling of crack boundaries captured microscopic failure transition from along grain boundaries to coalescence along the shear band, dominated by intraphase cracks. This novel framework presents a gateway into further understanding the behaviour of crystalline rocks and granular minerals.\n
\n\n\n\n \n\n \n \n \n \n \n In situ chemical oxidation processes: 4D quantitative visualization of byproduct formation and deposition via micro-CT imaging.\n \n \n \n\n\n \n Kalogerakis, G.; Zhao, Q.; Grasselli, G.; and Sleep, B.\n\n\n \n\n\n\n Leading Edge, 37(6). 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
\n\n\n \n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {In situ chemical oxidation processes: 4D quantitative visualization of byproduct formation and deposition via micro-CT imaging},\n type = {article},\n year = {2018},\n keywords = {Engineering,Environmental,Groundwater,Imaging,Tomography},\n volume = {37},\n id = {ec37481d-2f07-34eb-b1a2-91960ec49494},\n created = {2021-02-06T07:01:17.299Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.299Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2018 by The Society of Exploration Geophysicists. In Canada alone, petroleum hydrocarbons have been found in groundwater and soil at approximately 1400 and 4000 sites, respectively. In situ chemical oxidation (ISCO) is a remediation technology that delivers oxidants to the subsurface to mineralize the contaminants. A typical oxidant is permanganate, which generates carbon dioxide (CO2) as gas and manganese oxides (MnO2) as precipitates. In this study, microcomputed tomography (micro-CT) imaging has been used successfully to visualize the oxidation of diesel fuel with permanganate in a 1D column packed with silica sand with respect to time (4D imaging). The byproducts of diesel fuel oxidation with permanganate have been visualized with micro-CT image analysis and subsequently qualitatively and quantitatively assessed via image processing. This is the first study to visualize the distribution of the byproducts in the pores in a noninvasive manner and to quantify both the gaseous CO2 and MnO2. Flushing water through the sample to remove the byproducts was also investigated. Imaging results showed a reduction of the gas phase by approximately 6% from water flushing, but the MnO2 deposits were not removed. CO2 and MnO2 generation from permanganate addition for contaminant remediation may result in preferential pathways, and potential permanganate bypassing of the target treatment zone may occur, reducing the efficiency of the remediation process. Using 4D micro-CT imaging offers an opportunity to further elucidate the fundamental understanding of all underlying processes and potentially help in improving the design of ISCO schemes.},\n bibtype = {article},\n author = {Kalogerakis, G.C. and Zhao, Q. and Grasselli, G. and Sleep, B.E.},\n doi = {10.1190/tle37060462.1},\n journal = {Leading Edge},\n number = {6}\n}\n\n © 2018 by The Society of Exploration Geophysicists. In Canada alone, petroleum hydrocarbons have been found in groundwater and soil at approximately 1400 and 4000 sites, respectively. In situ chemical oxidation (ISCO) is a remediation technology that delivers oxidants to the subsurface to mineralize the contaminants. A typical oxidant is permanganate, which generates carbon dioxide (CO2) as gas and manganese oxides (MnO2) as precipitates. In this study, microcomputed tomography (micro-CT) imaging has been used successfully to visualize the oxidation of diesel fuel with permanganate in a 1D column packed with silica sand with respect to time (4D imaging). The byproducts of diesel fuel oxidation with permanganate have been visualized with micro-CT image analysis and subsequently qualitatively and quantitatively assessed via image processing. This is the first study to visualize the distribution of the byproducts in the pores in a noninvasive manner and to quantify both the gaseous CO2 and MnO2. Flushing water through the sample to remove the byproducts was also investigated. Imaging results showed a reduction of the gas phase by approximately 6% from water flushing, but the MnO2 deposits were not removed. CO2 and MnO2 generation from permanganate addition for contaminant remediation may result in preferential pathways, and potential permanganate bypassing of the target treatment zone may occur, reducing the efficiency of the remediation process. Using 4D micro-CT imaging offers an opportunity to further elucidate the fundamental understanding of all underlying processes and potentially help in improving the design of ISCO schemes.\n
\n\n\n\n \n\n \n \n \n \n \n Direct Observation of Faulting by Means of Rotary Shear Tests Under X-Ray Micro-Computed Tomography.\n \n \n \n\n\n \n Zhao, Q.; Tisato, N.; Kovaleva, O.; and Grasselli, G.\n\n\n \n\n\n\n Journal of Geophysical Research: Solid Earth, 123(9). 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
\n\n\n \n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {Direct Observation of Faulting by Means of Rotary Shear Tests Under X-Ray Micro-Computed Tomography},\n type = {article},\n year = {2018},\n keywords = {X-ray micro-CT,contact patch,critical slip distance,friction,real contact area,rotary shear experiment},\n volume = {123},\n id = {8dfb0a4d-6c3a-32da-aed4-557c1444f604},\n created = {2021-02-06T07:01:17.351Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.351Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {©2018. American Geophysical Union. All Rights Reserved. Friction and fault evolution are critical aspects in earthquake studies as they directly influence the nucleation, propagation, and arrest of earthquake ruptures. We present the results of a recently developed experimental approach that investigates these important aspects using a combination of rotary shear testing and X-ray micro-computed tomography technology. Two sets of experiments at normal stresses (σn) of 2.5 and 1.8 MPa were conducted on synthetic laboratory faults. We identified real contact areas (Ac) on the fault surfaces and estimated sizes of contact patches by means of micro-computed tomography image analysis. The number of contact patches and their sizes showed positive correlations with σn, and contact patch size distributions followed power law relations. The total number of contact patches decreased with increasing slip distance, and large contact patches endured longer slip distance than small ones. Secondary off-fault fractures created by interlocking and breakdown of large contact patches were closely related to the sudden drops of frictional resistance, suggesting the dominant role of surface roughness on shear behavior especially at low stress.},\n bibtype = {article},\n author = {Zhao, Q. and Tisato, N. and Kovaleva, O. and Grasselli, G.},\n doi = {10.1029/2017JB015394},\n journal = {Journal of Geophysical Research: Solid Earth},\n number = {9}\n}\n\n ©2018. American Geophysical Union. All Rights Reserved. Friction and fault evolution are critical aspects in earthquake studies as they directly influence the nucleation, propagation, and arrest of earthquake ruptures. We present the results of a recently developed experimental approach that investigates these important aspects using a combination of rotary shear testing and X-ray micro-computed tomography technology. Two sets of experiments at normal stresses (σn) of 2.5 and 1.8 MPa were conducted on synthetic laboratory faults. We identified real contact areas (Ac) on the fault surfaces and estimated sizes of contact patches by means of micro-computed tomography image analysis. The number of contact patches and their sizes showed positive correlations with σn, and contact patch size distributions followed power law relations. The total number of contact patches decreased with increasing slip distance, and large contact patches endured longer slip distance than small ones. Secondary off-fault fractures created by interlocking and breakdown of large contact patches were closely related to the sudden drops of frictional resistance, suggesting the dominant role of surface roughness on shear behavior especially at low stress.\n
\n\n\n\n \n\n \n \n \n \n \n Three new boundary conditions for the seismic response analysis of geomechanics problems using the numerical manifold method.\n \n \n \n\n\n \n Wei, W.; Zhao, Q.; Jiang, Q.; and Grasselli, G.\n\n\n \n\n\n\n International Journal of Rock Mechanics and Mining Sciences, 105. 2018.\n \n\n\n\n
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\n\n\n@article{\n title = {Three new boundary conditions for the seismic response analysis of geomechanics problems using the numerical manifold method},\n type = {article},\n year = {2018},\n keywords = {Free field boundary,Numerical manifold method,Seismic response analysis,Viscous boundary},\n volume = {105},\n id = {65d09fbf-4ceb-300c-893c-6d3429f8b4b2},\n created = {2021-02-06T07:01:17.372Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.372Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2018 Elsevier Ltd The numerical manifold method (NMM) provides a unified approach to address continuum-discontinuum problems in geotechnical engineering. Owing to the dynamic nature of its governing equations, the NMM should be suitable for modelling dynamic problems such as those associated to earthquakes. However, due to the current limitations in far-field boundary conditions implemented in the original NMM formulation, NMM has not been used to carry out seismic response analysis. In the present study, three new boundary conditions have been developed to extend the capability of the NMM to conduct seismic response analysis: (1) the classical viscous boundary condition, which allows for the absorption of the seismic wave energy at the boundaries, based on the viscous boundaries, and the seismic motion input method is also proposed; (2) the free field boundary condition, which captures the free field motion and absorption of the reflected waves at the sides of the model. The algorithms to generate free field mesh and its coupling calculations with the main mesh are also presented; (3) the static-dynamic unified boundary, which models the transition from fixed boundary condition in static state to free field boundary condition in seismic state, thus ensuring the accuracy and consistency of the numerical simulation. Finally, five numerical examples are shown to validate the proposed methods. The numerical results indicate that the improved NMM can be successfully adopted for seismic response analysis.},\n bibtype = {article},\n author = {Wei, W. and Zhao, Q. and Jiang, Q. and Grasselli, G.},\n doi = {10.1016/j.ijrmms.2018.03.009},\n journal = {International Journal of Rock Mechanics and Mining Sciences}\n}\n\n © 2018 Elsevier Ltd The numerical manifold method (NMM) provides a unified approach to address continuum-discontinuum problems in geotechnical engineering. Owing to the dynamic nature of its governing equations, the NMM should be suitable for modelling dynamic problems such as those associated to earthquakes. However, due to the current limitations in far-field boundary conditions implemented in the original NMM formulation, NMM has not been used to carry out seismic response analysis. In the present study, three new boundary conditions have been developed to extend the capability of the NMM to conduct seismic response analysis: (1) the classical viscous boundary condition, which allows for the absorption of the seismic wave energy at the boundaries, based on the viscous boundaries, and the seismic motion input method is also proposed; (2) the free field boundary condition, which captures the free field motion and absorption of the reflected waves at the sides of the model. The algorithms to generate free field mesh and its coupling calculations with the main mesh are also presented; (3) the static-dynamic unified boundary, which models the transition from fixed boundary condition in static state to free field boundary condition in seismic state, thus ensuring the accuracy and consistency of the numerical simulation. Finally, five numerical examples are shown to validate the proposed methods. The numerical results indicate that the improved NMM can be successfully adopted for seismic response analysis.\n
\n\n\n\n \n\n \n \n \n \n \n Dataset for time-lapse ultrasonic tomography of a granite slab under uniaxial compression test.\n \n \n \n\n\n \n Zhao, Q.; He, T.; Ha, J.; Xia, K.; and Grasselli, G.\n\n\n \n\n\n\n Data in Brief, 20. 2018.\n \n\n\n\n
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\n\n\n@article{\n title = {Dataset for time-lapse ultrasonic tomography of a granite slab under uniaxial compression test},\n type = {article},\n year = {2018},\n volume = {20},\n id = {de0207a6-6299-3a93-b844-f08ddbaaef58},\n created = {2021-02-06T07:01:17.421Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.421Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2018 This data article includes raw data for time-lapse ultrasonic tomography measurements during a uniaxial compression test. Two sets of experimental data are included: first, the ultrasonic tomography (UT) observation (i.e., waveform) data at each 20 MPa axial stress step during the uniaxial loading test; and second, the stress-strain curve of the uniaxial compression test. A numerical model based on the combined finite-discrete element method (FDEM) was used to improve the understanding of the experimental results. The model file and the simulated acoustic emission (AE) data extracted from the simulation results are also included in this article. Data sets presented in this article help to improve understanding of the progressive rock failure process at microscopic and macroscopic scales.},\n bibtype = {article},\n author = {Zhao, Q. and He, T.-M. and Ha, J. and Xia, K. and Grasselli, G.},\n doi = {10.1016/j.dib.2018.08.151},\n journal = {Data in Brief}\n}\n\n © 2018 This data article includes raw data for time-lapse ultrasonic tomography measurements during a uniaxial compression test. Two sets of experimental data are included: first, the ultrasonic tomography (UT) observation (i.e., waveform) data at each 20 MPa axial stress step during the uniaxial loading test; and second, the stress-strain curve of the uniaxial compression test. A numerical model based on the combined finite-discrete element method (FDEM) was used to improve the understanding of the experimental results. The model file and the simulated acoustic emission (AE) data extracted from the simulation results are also included in this article. Data sets presented in this article help to improve understanding of the progressive rock failure process at microscopic and macroscopic scales.\n
\n\n\n\n \n\n \n \n \n \n \n Understanding progressive rock failure and associated seismicity using ultrasonic tomography and numerical simulation.\n \n \n \n\n\n \n He, T.; Zhao, Q.; Ha, J.; Xia, K.; and Grasselli, G.\n\n\n \n\n\n\n Tunnelling and Underground Space Technology, 81. 2018.\n \n\n\n\n
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\n\n\n@article{\n title = {Understanding progressive rock failure and associated seismicity using ultrasonic tomography and numerical simulation},\n type = {article},\n year = {2018},\n keywords = {AE,FDEM,Precursors,Ultrasonic tomography,b-value},\n volume = {81},\n id = {1821b2c1-f24e-3a5d-9ef9-fa3e4ac2ba7f},\n created = {2021-02-06T07:01:17.450Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.450Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2018 The Authors Monitoring the stability of underground rock excavation zones, such as tunnels and underground mines, is critical to their operational safety. The stability of these structures is related to the stress redistribution introduced by the excavation process and disturbance during the operation. Therefore, the characteristics of progressive rock failure behaviour at different stress conditions must be investigated. In this study, we address this problem using a laboratory experiment, coupled with ultrasonic tomography (UT) and numerical simulation. A time-lapse two-dimensional (2D) UT observation was conducted on a granite slab under uniaxial compression. This test was then reproduced numerically by the combined finite-discrete element method (FDEM). This innovative combination of technologies depicted the entire deformation and failure processes at macroscopic and microscopic scales. Quantitative assessments of the results suggested six precursory behaviours indicating the catastrophic failure of the rock: (1) decrease of the average wave velocity perpendicular to the loading direction, (2) increase of the heterogeneity and anisotropy of wave velocity, (3) exponential increase of seismic rate, (4) spatial localization of damage onto the failure plane, (5) increase of the dominance of shear failure, and (6) slight recovery of b-value, followed by a significant drop. An integrated monitoring and analysis of these indicators, accompanied by carefully calibrated numerical simulations, may provide vital information regarding the stability of underground structures.},\n bibtype = {article},\n author = {He, T.-M. and Zhao, Q. and Ha, J. and Xia, K. and Grasselli, G.},\n doi = {10.1016/j.tust.2018.06.022},\n journal = {Tunnelling and Underground Space Technology}\n}\n\n © 2018 The Authors Monitoring the stability of underground rock excavation zones, such as tunnels and underground mines, is critical to their operational safety. The stability of these structures is related to the stress redistribution introduced by the excavation process and disturbance during the operation. Therefore, the characteristics of progressive rock failure behaviour at different stress conditions must be investigated. In this study, we address this problem using a laboratory experiment, coupled with ultrasonic tomography (UT) and numerical simulation. A time-lapse two-dimensional (2D) UT observation was conducted on a granite slab under uniaxial compression. This test was then reproduced numerically by the combined finite-discrete element method (FDEM). This innovative combination of technologies depicted the entire deformation and failure processes at macroscopic and microscopic scales. Quantitative assessments of the results suggested six precursory behaviours indicating the catastrophic failure of the rock: (1) decrease of the average wave velocity perpendicular to the loading direction, (2) increase of the heterogeneity and anisotropy of wave velocity, (3) exponential increase of seismic rate, (4) spatial localization of damage onto the failure plane, (5) increase of the dominance of shear failure, and (6) slight recovery of b-value, followed by a significant drop. An integrated monitoring and analysis of these indicators, accompanied by carefully calibrated numerical simulations, may provide vital information regarding the stability of underground structures.\n
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\n \n \n\n \n \n \n \n \n Rotary shear experiments under X-ray micro-computed tomography.\n \n \n \n\n\n \n Zhao, Q.; Tisato, N.; and Grasselli, G.\n\n\n \n\n\n\n Review of Scientific Instruments, 88(1). 2017.\n \n\n\n\n
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\n\n\n@article{\n title = {Rotary shear experiments under X-ray micro-computed tomography},\n type = {article},\n year = {2017},\n volume = {88},\n id = {0d552f7a-2b90-338d-af5d-35e461714d7c},\n created = {2021-02-06T07:01:17.097Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.097Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2017 Author(s). A rotary shear apparatus (ERDμ-T) was designed, assembled, and calibrated to study frictional behavior. We paired the apparatus with X-ray micro-computed tomography (μCT) to inspect in situ and in operando deformation of the tested specimen. This technology allows us to observe how two rough surfaces interact and deform without perturbing the experimental conditions (e.g., pressure, temperature, and sample position). We performed an experiment employing an aluminum alloy sample to demonstrate the capability of the apparatus. The sample was sheared at incremental steps, and during shearing, normal force, sample shortening, torque, and shearing velocity were measured. The measurements were associated to the μCT imagery, giving a comprehensive understanding of the deformation processes of the samples. The present contribution demonstrates that the ERDμ-T allows (1) linking the variation of physical parameters to the evolution of internal structures of the sample and (2) shedding light on fracturing and frictional sliding processes in solid materials.},\n bibtype = {article},\n author = {Zhao, Q. and Tisato, N. and Grasselli, G.},\n doi = {10.1063/1.4974149},\n journal = {Review of Scientific Instruments},\n number = {1}\n}\n\n © 2017 Author(s). A rotary shear apparatus (ERDμ-T) was designed, assembled, and calibrated to study frictional behavior. We paired the apparatus with X-ray micro-computed tomography (μCT) to inspect in situ and in operando deformation of the tested specimen. This technology allows us to observe how two rough surfaces interact and deform without perturbing the experimental conditions (e.g., pressure, temperature, and sample position). We performed an experiment employing an aluminum alloy sample to demonstrate the capability of the apparatus. The sample was sheared at incremental steps, and during shearing, normal force, sample shortening, torque, and shearing velocity were measured. The measurements were associated to the μCT imagery, giving a comprehensive understanding of the deformation processes of the samples. The present contribution demonstrates that the ERDμ-T allows (1) linking the variation of physical parameters to the evolution of internal structures of the sample and (2) shedding light on fracturing and frictional sliding processes in solid materials.\n
\n\n\n\n \n\n \n \n \n \n \n Direct observation of faulting by means of a rotary shear test under X-ray micro-computed tomography.\n \n \n \n\n\n \n Zhao, Q.; Tisato, N.; Kovaleva, O.; and Grasselli, G.\n\n\n \n\n\n\n 2017.\n \n\n\n\n
\n\n\n\n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
\n\n\n \n\n\n\n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
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\n\n\n@misc{\n title = {Direct observation of faulting by means of a rotary shear test under X-ray micro-computed tomography},\n type = {misc},\n year = {2017},\n source = {arXiv},\n id = {de2d8ca0-dab8-3620-9b38-cd9e4efbf22d},\n created = {2021-02-06T07:01:17.186Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.186Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {Copyright © 2017, The Authors. All rights reserved. Friction and fault surface evolution are critical aspects in earthquake studies. We present the preliminary result from a novel experimental approach that combines rotary shear testing with X-ray micro-computed tomography (µCT) technology. An artificial fault was sheared at small incremental rotational steps under the normal stress of 2.5 MPa. During shearing, mechanical data including normal force and torque were measured and used to calculate the friction coefficient (µ). After each rotation increment, a µCT scan was conducted to observe the sample structure. The careful and quantitative µCT image analysis allowed for direct and continuous observation of the fault evolution. We observed that fracturing due to asperity interlocking and breakage dominated the initial phase of slipping. The frictional behavior stabilized after ∼1 mm slip distance, which inferred the critical slip distance (Dc). We developed a novel approach to estimate the real contact area (Ac) on the fault surface by means of µCT image analysis. Ac varied with increased shear distances as the contacts between asperities changed, and it eventually stabilized at approximately 12% of the nominal fault area. The dimension of the largest contact patch on the surface was close to observed Dc, suggesting that the frictional behavior may be controlled by contacting large asperities. These observations improved our understanding of fault evolution and associated friction variation. Moreover, this work demonstrates that the µCT technology is a powerful tool for the study of earthquake physics.},\n bibtype = {misc},\n author = {Zhao, Q. and Tisato, N. and Kovaleva, O. and Grasselli, G.}\n}\n\n Copyright © 2017, The Authors. All rights reserved. Friction and fault surface evolution are critical aspects in earthquake studies. We present the preliminary result from a novel experimental approach that combines rotary shear testing with X-ray micro-computed tomography (µCT) technology. An artificial fault was sheared at small incremental rotational steps under the normal stress of 2.5 MPa. During shearing, mechanical data including normal force and torque were measured and used to calculate the friction coefficient (µ). After each rotation increment, a µCT scan was conducted to observe the sample structure. The careful and quantitative µCT image analysis allowed for direct and continuous observation of the fault evolution. We observed that fracturing due to asperity interlocking and breakage dominated the initial phase of slipping. The frictional behavior stabilized after ∼1 mm slip distance, which inferred the critical slip distance (Dc). We developed a novel approach to estimate the real contact area (Ac) on the fault surface by means of µCT image analysis. Ac varied with increased shear distances as the contacts between asperities changed, and it eventually stabilized at approximately 12% of the nominal fault area. The dimension of the largest contact patch on the surface was close to observed Dc, suggesting that the frictional behavior may be controlled by contacting large asperities. These observations improved our understanding of fault evolution and associated friction variation. Moreover, this work demonstrates that the µCT technology is a powerful tool for the study of earthquake physics.\n
\n\n\n\n \n\n \n \n \n \n \n Understanding progressive rock failure using ultrasonic tomography and numerical simulation.\n \n \n \n\n\n \n Zhao, Q.; Abdelaziz, A.; He, T.; Xia, K.; and Grasselli, G.\n\n\n \n\n\n\n In ISRM Progressive Rock Failure Conference, PRF 2017, volume 2017-June, 2017. \n \n\n\n\n
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\n\n\n\n@inproceedings{\n title = {Understanding progressive rock failure using ultrasonic tomography and numerical simulation},\n type = {inproceedings},\n year = {2017},\n volume = {2017-June},\n id = {26cd2c8e-6afd-337a-9e07-26543edebb0a},\n created = {2021-02-06T07:01:17.467Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.467Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n bibtype = {inproceedings},\n author = {Zhao, Q. and Abdelaziz, A. and He, T.-M. and Xia, K. and Grasselli, G.},\n booktitle = {ISRM Progressive Rock Failure Conference, PRF 2017}\n}\n\n \n\n \n \n \n \n \n Numerical simulation on seismic response of the filled joint under high amplitude stress waves using Finite-Discrete Element Method (FDEM).\n \n \n \n\n\n \n Huang, X.; Zhao, Q.; Qi, S.; Xia, K.; Grasselli, G.; and Chen, X.\n\n\n \n\n\n\n Materials, 10(1). 2017.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
\n\n\n\n\n\n \n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {Numerical simulation on seismic response of the filled joint under high amplitude stress waves using Finite-Discrete Element Method (FDEM)},\n type = {article},\n year = {2017},\n keywords = {Amplitude attenuation,FDEM,Filled joint,Grain size reduction,High amplitude stress wave,Particle crushing},\n volume = {10},\n id = {cbb1e597-64a9-3981-8a14-ae28cb1c03d3},\n created = {2021-02-06T07:01:17.636Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.636Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2017 by the authors. This paper numerically investigates the seismic response of the filled joint under high amplitude stress waves using the combined finite-discrete element method (FDEM). A thin layer of independent polygonal particles are used to simulate the joint fillings. Each particle is meshed using the Delaunay triangulation scheme and can be crushed when the load exceeds its strength. The propagation of the 1D longitude wave through a single filled joint is studied, considering the influences of the joint thickness and the characteristics of the incident wave, such as the amplitude and frequency. The results show that the filled particles under high amplitude stress waves mainly experience three deformation stages: (i) initial compaction stage; (ii) crushing stage; and (iii) crushing and compaction stage. In the initial compaction stage and crushing and compaction stage, compaction dominates the mechanical behavior of the joint, and the particle area distribution curve varies little. In these stages, the transmission coefficient increases with the increase of the amplitude, i.e., peak particle velocity (PPV), of the incident wave. On the other hand, in the crushing stage, particle crushing plays the dominant role. The particle size distribution curve changes abruptly with the PPV due to the fragments created by the crushing process. This process consumes part of wave energy and reduces the stiffness of the filled joint. The transmission coefficient decreases with increasing PPV in this stage because of the increased amount of energy consumed by crushing. Moreover, with the increase of the frequency of the incident wave, the transmission coefficient decreases and fewer particles can be crushed. Under the same incident wave, the transmission coefficient decreases when the filled thickness increases and the filled particles become more difficult to be crushed.},\n bibtype = {article},\n author = {Huang, X. and Zhao, Q. and Qi, S. and Xia, K. and Grasselli, G. and Chen, X.},\n doi = {10.3390/ma10010013},\n journal = {Materials},\n number = {1}\n}\n\n © 2017 by the authors. This paper numerically investigates the seismic response of the filled joint under high amplitude stress waves using the combined finite-discrete element method (FDEM). A thin layer of independent polygonal particles are used to simulate the joint fillings. Each particle is meshed using the Delaunay triangulation scheme and can be crushed when the load exceeds its strength. The propagation of the 1D longitude wave through a single filled joint is studied, considering the influences of the joint thickness and the characteristics of the incident wave, such as the amplitude and frequency. The results show that the filled particles under high amplitude stress waves mainly experience three deformation stages: (i) initial compaction stage; (ii) crushing stage; and (iii) crushing and compaction stage. In the initial compaction stage and crushing and compaction stage, compaction dominates the mechanical behavior of the joint, and the particle area distribution curve varies little. In these stages, the transmission coefficient increases with the increase of the amplitude, i.e., peak particle velocity (PPV), of the incident wave. On the other hand, in the crushing stage, particle crushing plays the dominant role. The particle size distribution curve changes abruptly with the PPV due to the fragments created by the crushing process. This process consumes part of wave energy and reduces the stiffness of the filled joint. The transmission coefficient decreases with increasing PPV in this stage because of the increased amount of energy consumed by crushing. Moreover, with the increase of the frequency of the incident wave, the transmission coefficient decreases and fewer particles can be crushed. Under the same incident wave, the transmission coefficient decreases when the filled thickness increases and the filled particles become more difficult to be crushed.\n
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\n \n \n\n \n \n \n \n \n Experimental rock deformation under micro-CT - Two new apparatuses for rock physics.\n \n \n \n\n\n \n Tisato, N.; Zhao, Q.; and Grasselli, G.\n\n\n \n\n\n\n In 78th EAGE Conference and Exhibition 2016: Efficient Use of Technology - Unlocking Potential, 2016. \n \n\n\n\n
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\n\n\n@inproceedings{\n title = {Experimental rock deformation under micro-CT - Two new apparatuses for rock physics},\n type = {inproceedings},\n year = {2016},\n id = {ca3812b9-dd43-3bbc-9039-5413853ee159},\n created = {2021-02-06T07:01:16.989Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:16.989Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {Geophysical methods rely on the accurate determination of physical and mechanical properties of rocks. However, these properties are intimately related to microscopic features such as pore shape and distribution, grain orientations, degree of saturation and fluid distribution. The present contribution reports the development and the preliminary results obtained with two new high pressure vessels which are paired with a X-ray micro-CT system to investigate the influence of fluid distribution and microstructural features on the physical and mechanical properties of rocks, and in particular on seismic wave attenuation and dynamic moduli.},\n bibtype = {inproceedings},\n author = {Tisato, N. and Zhao, Q. and Grasselli, G.},\n doi = {10.3997/2214-4609.201601225},\n booktitle = {78th EAGE Conference and Exhibition 2016: Efficient Use of Technology - Unlocking Potential}\n}\n\n Geophysical methods rely on the accurate determination of physical and mechanical properties of rocks. However, these properties are intimately related to microscopic features such as pore shape and distribution, grain orientations, degree of saturation and fluid distribution. The present contribution reports the development and the preliminary results obtained with two new high pressure vessels which are paired with a X-ray micro-CT system to investigate the influence of fluid distribution and microstructural features on the physical and mechanical properties of rocks, and in particular on seismic wave attenuation and dynamic moduli.\n
\n\n\n\n \n\n \n \n \n \n \n Experimental rock physics under micro-CT.\n \n \n \n\n\n \n Tisato, N.; Zhao, Q.; and Grasselli, G.\n\n\n \n\n\n\n In SEG Technical Program Expanded Abstracts, volume 35, 2016. \n \n\n\n\n
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\n\n\n@inproceedings{\n title = {Experimental rock physics under micro-CT},\n type = {inproceedings},\n year = {2016},\n volume = {35},\n id = {2d11fa17-5a1f-3d6b-8f7b-7a908be063fe},\n created = {2021-02-06T07:01:17.081Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.081Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2016 SEG. Geophysical methods rely on the accurate determination of physical and mechanical properties of rocks. These properties are intimately related to rock microscopic features such as pore shape and distribution, grain orientations, and fluid distribution. The present contribution reports the preliminary results obtained with a newly conceived high pressure vessel which is paired with an X-ray micro-CT system to investigate the influence of fluid distribution and microstructural features on the physical and mechanical properties of rocks, and in particular on seismic wave attenuation and dynamic moduli.},\n bibtype = {inproceedings},\n author = {Tisato, N. and Zhao, Q. and Grasselli, G.},\n doi = {10.1190/segam2016-13949603.1},\n booktitle = {SEG Technical Program Expanded Abstracts}\n}\n\n © 2016 SEG. Geophysical methods rely on the accurate determination of physical and mechanical properties of rocks. These properties are intimately related to rock microscopic features such as pore shape and distribution, grain orientations, and fluid distribution. The present contribution reports the preliminary results obtained with a newly conceived high pressure vessel which is paired with an X-ray micro-CT system to investigate the influence of fluid distribution and microstructural features on the physical and mechanical properties of rocks, and in particular on seismic wave attenuation and dynamic moduli.\n
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\n \n \n\n \n \n \n \n \n Seismic wave attenuation in rocks saturated with bubbly liquids: Experiments and numerical modeling.\n \n \n \n\n\n \n Tisato, N.; Chapman, S.; Zhao, Q.; Grasselli, G.; and Quintal, B.\n\n\n \n\n\n\n In SEG Technical Program Expanded Abstracts, volume 34, 2015. \n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
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\n\n\n@inproceedings{\n title = {Seismic wave attenuation in rocks saturated with bubbly liquids: Experiments and numerical modeling},\n type = {inproceedings},\n year = {2015},\n volume = {34},\n id = {8709b878-25de-3dab-9ab5-d6f5d5c3b5d1},\n created = {2021-02-06T07:01:17.501Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.501Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2015 SEG. Seismic wave attenuation (1/Q) is a physical property that might be considered in seismic tomography to improve the subsurface imaging. In particular, it may help in the exploration of unconventional reservoirs as these resources are hosted in highly attenuating geo-materials. One of the factors increasing visco-elasticity of rocks (i.e. 1/Q) is the presence of fluids. Here we report experimental data showing how gas bubbles, occupying part of water-saturated pores, attenuate seismic waves. The data are explained with a gas-exsolution-dissolution theory and a 1D numerical model accounting for the diffusion of the gas in the water. The theory is then applied to an oil-methane system showing that this attenuation mechanism is relevant also for hydrocarbon reservoirs.},\n bibtype = {inproceedings},\n author = {Tisato, N. and Chapman, S. and Zhao, Q. and Grasselli, G. and Quintal, B.},\n doi = {10.1190/segam2015-5902520.1},\n booktitle = {SEG Technical Program Expanded Abstracts}\n}\n\n © 2015 SEG. Seismic wave attenuation (1/Q) is a physical property that might be considered in seismic tomography to improve the subsurface imaging. In particular, it may help in the exploration of unconventional reservoirs as these resources are hosted in highly attenuating geo-materials. One of the factors increasing visco-elasticity of rocks (i.e. 1/Q) is the presence of fluids. Here we report experimental data showing how gas bubbles, occupying part of water-saturated pores, attenuate seismic waves. The data are explained with a gas-exsolution-dissolution theory and a 1D numerical model accounting for the diffusion of the gas in the water. The theory is then applied to an oil-methane system showing that this attenuation mechanism is relevant also for hydrocarbon reservoirs.\n
\n\n\n\n \n\n \n \n \n \n \n Influence of in situ stress variations on acoustic emissions: A numerical study.\n \n \n \n\n\n \n Zhao, Q.; Tisato, N.; Grasselli, G.; Mahabadi, O.; Lisjak, A.; and Liu, Q.\n\n\n \n\n\n\n Geophysical Journal International, 203(2). 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n \n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n\n\n\n
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\n\n\n@article{\n title = {Influence of in situ stress variations on acoustic emissions: A numerical study},\n type = {article},\n year = {2015},\n keywords = {Earthquake source observations,Fractures and faults,Mechanics, theory, and modelling,Numerical solutions,Statistical seismology},\n volume = {203},\n id = {9b0a485d-5140-326c-9cc8-d44d9b657ffb},\n created = {2018-05-30T23:59:00.000Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-28T23:42:18.705Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {true},\n abstract = {© The Authors 2015. The study of acoustic emissions (AEs) is of paramount importance to understand rock deformation processes. AE recorded during laboratory experiments mimics, in a controlled geometry and environment, natural and induced seismicity. However, these experiments are destructive, time consuming and require a significant amount of resources. Lately, significant progresses have been made in numerical simulations of rock failure processes, providing detailed insights into AE. We utilized the 2-D combined finite-discrete element method to simulate the deformation of Stanstead Granite under varying confining pressure (Pc) and demonstrated that the increase of confining pressure, Pc, (i) shifts failures from tensile towards shear dominated and (ii) enhance the macroscopic ductility. We quantitatively describe the AE activity associated with the fracturing process by assessing the spatial fractal dimension (D-value), the temporal distribution (AE rate) and the slope of the frequency-magnitude distribution (b-value). Based on the evaluation of D-value and AE rate, we defined two distinct deformation phases: Phase I and Phase II. The influence of Pc on the spatial distribution of AE varies according to the deformation phase: for increasing Pc, D-value decreases and increases during Phases I and II, respectively. In addition, b-value decreases with increasing Pc during the entire experiment. Our numerical results show for the first time that variations of D- and b-values as a function of in situ stress can be simulated using the combined finite-discrete element approach. We demonstrate that the examination of seismicity should be carried out carefully, taking into consideration the deformation phase and in situ stress conditions.},\n bibtype = {article},\n author = {Zhao, Q. and Tisato, N. and Grasselli, G. and Mahabadi, O.K. and Lisjak, A. and Liu, Q.},\n doi = {10.1093/gji/ggv370},\n journal = {Geophysical Journal International},\n number = {2}\n}\n\n © The Authors 2015. The study of acoustic emissions (AEs) is of paramount importance to understand rock deformation processes. AE recorded during laboratory experiments mimics, in a controlled geometry and environment, natural and induced seismicity. However, these experiments are destructive, time consuming and require a significant amount of resources. Lately, significant progresses have been made in numerical simulations of rock failure processes, providing detailed insights into AE. We utilized the 2-D combined finite-discrete element method to simulate the deformation of Stanstead Granite under varying confining pressure (Pc) and demonstrated that the increase of confining pressure, Pc, (i) shifts failures from tensile towards shear dominated and (ii) enhance the macroscopic ductility. We quantitatively describe the AE activity associated with the fracturing process by assessing the spatial fractal dimension (D-value), the temporal distribution (AE rate) and the slope of the frequency-magnitude distribution (b-value). Based on the evaluation of D-value and AE rate, we defined two distinct deformation phases: Phase I and Phase II. The influence of Pc on the spatial distribution of AE varies according to the deformation phase: for increasing Pc, D-value decreases and increases during Phases I and II, respectively. In addition, b-value decreases with increasing Pc during the entire experiment. Our numerical results show for the first time that variations of D- and b-values as a function of in situ stress can be simulated using the combined finite-discrete element approach. We demonstrate that the examination of seismicity should be carried out carefully, taking into consideration the deformation phase and in situ stress conditions.\n
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\n \n \n\n \n \n \n \n \n Numerical simulation of hydraulic fracturing and associated microseismicity using finite-discrete element method.\n \n \n \n\n\n \n Zhao, Q.; Lisjak, A.; Mahabadi, O.; Liu, Q.; and Grasselli, G.\n\n\n \n\n\n\n Journal of Rock Mechanics and Geotechnical Engineering, 6(6). 2014.\n \n\n\n\n
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\n\n\n@article{\n title = {Numerical simulation of hydraulic fracturing and associated microseismicity using finite-discrete element method},\n type = {article},\n year = {2014},\n keywords = {Clustering,Finite-discrete element method (FDEM),Hydraulic fracturing (HF),Kernel density estimation (KDE),Microseismic (MS),Numerical simulation},\n volume = {6},\n id = {7fd62eab-504d-3122-9c9d-156f8ea935be},\n created = {2021-02-06T07:01:17.511Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.511Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Hydraulic fracturing (HF) technique has been extensively used for the exploitation of unconventional oil and gas reservoirs. HF enhances the connectivity of less permeable oil and gas-bearing rock formations by fluid injection, which creates an interconnected fracture network and increases the hydrocarbon production. Meanwhile, microseismic (MS) monitoring is one of the most effective approaches to evaluate such stimulation process. In this paper, the combined finite-discrete element method (FDEM) is adopted to numerically simulate HF and associated MS. Several post-processing tools, including frequency-magnitude distribution (b-value), fractal dimension (D-value), and seismic events clustering, are utilized to interpret numerical results. A non-parametric clustering algorithm designed specifically for FDEM is used to reduce the mesh dependency and extract more realistic seismic information. Simulation results indicated that at the local scale, the HF process tends to propagate following the rock mass discontinuities; while at the reservoir scale, it tends to develop in the direction parallel to the maximum in-situ stress.},\n bibtype = {article},\n author = {Zhao, Q. and Lisjak, A. and Mahabadi, O. and Liu, Q. and Grasselli, G.},\n doi = {10.1016/j.jrmge.2014.10.003},\n journal = {Journal of Rock Mechanics and Geotechnical Engineering},\n number = {6}\n}\n\n © 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Hydraulic fracturing (HF) technique has been extensively used for the exploitation of unconventional oil and gas reservoirs. HF enhances the connectivity of less permeable oil and gas-bearing rock formations by fluid injection, which creates an interconnected fracture network and increases the hydrocarbon production. Meanwhile, microseismic (MS) monitoring is one of the most effective approaches to evaluate such stimulation process. In this paper, the combined finite-discrete element method (FDEM) is adopted to numerically simulate HF and associated MS. Several post-processing tools, including frequency-magnitude distribution (b-value), fractal dimension (D-value), and seismic events clustering, are utilized to interpret numerical results. A non-parametric clustering algorithm designed specifically for FDEM is used to reduce the mesh dependency and extract more realistic seismic information. Simulation results indicated that at the local scale, the HF process tends to propagate following the rock mass discontinuities; while at the reservoir scale, it tends to develop in the direction parallel to the maximum in-situ stress.\n
\n\n\n\n \n\n \n \n \n \n \n Spectral-element simulations of elastic wave propagation in exploration and geotechnical applications.\n \n \n \n\n\n \n Zheng, L.; Zhao, Q.; Milkereit, B.; Grasselli, G.; and Liu, Q.\n\n\n \n\n\n\n Earthquake Science, 27(2). 2014.\n \n\n\n\n
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\n\n\n@article{\n title = {Spectral-element simulations of elastic wave propagation in exploration and geotechnical applications},\n type = {article},\n year = {2014},\n keywords = {Exploration seismology,Seismic wave propagation,Spectral-element method},\n volume = {27},\n id = {3bc5bec3-39f7-3907-9f7d-6387a217b6bc},\n created = {2021-02-06T07:01:17.550Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.550Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {We apply the spectral-element method (SEM), a high-order finite-element method (FEM) to simulate seismic wave propagation in complex media for exploration and geotechnical problems. The SEM accurately treats geometrical complexities through its flexible FEM mesh and accurately interpolates wavefields through high-order Lagrange polynomials. It has been a numerical solver used extensively in earthquake seismology. We demonstrate the applicability of SEM for selected 2D exploration and geotechnical velocity models with an open-source SEM software package SPECFEM2D. The first scenario involves a marine survey for a salt dome with the presence of major internal discontinuities, and the second example simulates seismic wave propagation for an open-pit mine with complex surface topography. Wavefield snapshots, synthetic seismograms, and peak particle velocity maps are presented to illustrate the promising use of SEM for industrial problems. © 2014 The Seismological Society of China, Institute of Geophysics, China Earthquake Administration and Springer-Verlag Berlin Heidelberg.},\n bibtype = {article},\n author = {Zheng, L. and Zhao, Q. and Milkereit, B. and Grasselli, G. and Liu, Q.},\n doi = {10.1007/s11589-014-0069-9},\n journal = {Earthquake Science},\n number = {2}\n}\n\n We apply the spectral-element method (SEM), a high-order finite-element method (FEM) to simulate seismic wave propagation in complex media for exploration and geotechnical problems. The SEM accurately treats geometrical complexities through its flexible FEM mesh and accurately interpolates wavefields through high-order Lagrange polynomials. It has been a numerical solver used extensively in earthquake seismology. We demonstrate the applicability of SEM for selected 2D exploration and geotechnical velocity models with an open-source SEM software package SPECFEM2D. The first scenario involves a marine survey for a salt dome with the presence of major internal discontinuities, and the second example simulates seismic wave propagation for an open-pit mine with complex surface topography. Wavefield snapshots, synthetic seismograms, and peak particle velocity maps are presented to illustrate the promising use of SEM for industrial problems. © 2014 The Seismological Society of China, Institute of Geophysics, China Earthquake Administration and Springer-Verlag Berlin Heidelberg.\n
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\n \n \n\n \n \n \n \n \n Numerical simulation of acoustic emission in rocks using FEM/DEM.\n \n \n \n\n\n \n Grasselli, G.; Zhao, Q.; Lisjak, A.; and Liu, Q.\n\n\n \n\n\n\n 2013.\n \n\n\n\n
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\n\n\n@book{\n title = {Numerical simulation of acoustic emission in rocks using FEM/DEM},\n type = {book},\n year = {2013},\n source = {Rock Dynamics and Applications - State of the Art},\n id = {6e563768-e186-3738-aef1-92c47d193898},\n created = {2021-02-06T07:01:17.314Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.314Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {© 2013 Taylor & Francis Group, London. Acoustic Emissions (AE) are stress waves released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical methods have been developed to simulate the deformation and damage processes of rocks, only a limited number have been capable of providing quantitative information regarding the associated acoustic activity. FEM/DEM is a numerical tool that simulates material failure by explicitly modelling fracture nucleation and propagation using cohesive elements. Seismic information is extracted with a newly developed algorithm based on the monitoring of internal variables in the proximity of propagating cracks. Several simulation cases were analyzed, including a point source model, a wing crack propagation model, and a circular excavation model. Simulated AE were cross-analyzed by travel-time inversion, spectral analysis, and frequency- magnitude statistics. These preliminary results demonstrate the capabilities of FEM/DEM as a tool to numerically simulate seismicity associated to the rock failure process.},\n bibtype = {book},\n author = {Grasselli, G. and Zhao, Q. and Lisjak, A. and Liu, Q.}\n}\n\n © 2013 Taylor & Francis Group, London. Acoustic Emissions (AE) are stress waves released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical methods have been developed to simulate the deformation and damage processes of rocks, only a limited number have been capable of providing quantitative information regarding the associated acoustic activity. FEM/DEM is a numerical tool that simulates material failure by explicitly modelling fracture nucleation and propagation using cohesive elements. Seismic information is extracted with a newly developed algorithm based on the monitoring of internal variables in the proximity of propagating cracks. Several simulation cases were analyzed, including a point source model, a wing crack propagation model, and a circular excavation model. Simulated AE were cross-analyzed by travel-time inversion, spectral analysis, and frequency- magnitude statistics. These preliminary results demonstrate the capabilities of FEM/DEM as a tool to numerically simulate seismicity associated to the rock failure process.\n
\n\n\n\n \n\n \n \n \n \n \n Numerical simulation of acoustic emission in rocks using FEM/DEM.\n \n \n \n\n\n \n Grasselli, G.; Zhao, Q.; Lisjak, A.; and Liu, Q.\n\n\n \n\n\n\n In Rock Dynamics and Applications - State of the Art: Proceedings of the 1st International Conference on Rock Dynamics and Applications, RocDyn-1 2013, 2013. \n \n\n\n\n
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\n\n\n@inproceedings{\n title = {Numerical simulation of acoustic emission in rocks using FEM/DEM},\n type = {inproceedings},\n year = {2013},\n id = {3d788bb2-e17b-3ba7-8988-4e8e11b5a74b},\n created = {2021-02-06T07:01:17.399Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.399Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {Acoustic Emissions (AE) are stress waves released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical methods have been developed to simulate the deformation and damage processes of rocks, only a limited number have been capable of providing quantitative information regarding the associated acoustic activity. FEM/DEM is a numerical tool that simulates material failure by explicitly modelling fracture nucleation and propagation using cohesive elements. Seismic information is extracted with a newly developed algorithm based on the monitoring of internal variables in the proximity of propagating cracks. Several simulation cases were analyzed, including a point source model, a wing crack propagation model, and a circular excavation model. Simulated AE were cross-analyzed by travel-time inversion, spectral analysis, and frequency-magnitude statistics. These preliminary results demonstrate the capabilities of FEM/DEM as a tool to numerically simulate seismicity associated to the rock failure process. © 2013 Taylor & Francis Group.},\n bibtype = {inproceedings},\n author = {Grasselli, G. and Zhao, Q. and Lisjak, A. and Liu, Q.},\n booktitle = {Rock Dynamics and Applications - State of the Art: Proceedings of the 1st International Conference on Rock Dynamics and Applications, RocDyn-1 2013}\n}\n\n Acoustic Emissions (AE) are stress waves released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical methods have been developed to simulate the deformation and damage processes of rocks, only a limited number have been capable of providing quantitative information regarding the associated acoustic activity. FEM/DEM is a numerical tool that simulates material failure by explicitly modelling fracture nucleation and propagation using cohesive elements. Seismic information is extracted with a newly developed algorithm based on the monitoring of internal variables in the proximity of propagating cracks. Several simulation cases were analyzed, including a point source model, a wing crack propagation model, and a circular excavation model. Simulated AE were cross-analyzed by travel-time inversion, spectral analysis, and frequency-magnitude statistics. These preliminary results demonstrate the capabilities of FEM/DEM as a tool to numerically simulate seismicity associated to the rock failure process. © 2013 Taylor & Francis Group.\n
\n\n\n\n \n\n \n \n \n \n \n Erratum to Numerical simulation of acoustic emission in brittle rocks by two-dimensional finite-discrete element analysis [Geophys. J. Int., 195, (2013), 423].\n \n \n \n\n\n \n Lisjak, A.; Liu, Q.; Zhao, Q.; Mahabadi, O.; and Grasselli, G.\n\n\n \n\n\n\n Geophysical Journal International, 196(2). 2013.\n \n\n\n\n
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\n\n\n\n@article{\n title = {Erratum to Numerical simulation of acoustic emission in brittle rocks by two-dimensional finite-discrete element analysis [Geophys. J. Int., 195, (2013), 423]},\n type = {article},\n year = {2013},\n volume = {196},\n id = {55372ae2-af2d-377a-8092-96b9411ff18b},\n created = {2021-02-06T07:01:17.566Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.566Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n bibtype = {article},\n author = {Lisjak, A. and Liu, Q. and Zhao, Q. and Mahabadi, O.K. and Grasselli, G.},\n doi = {10.1093/gji/ggt419},\n journal = {Geophysical Journal International},\n number = {2}\n}\n\n \n\n \n \n \n \n \n Numerical simulation of acoustic emission in brittle rocks by two-dimensional finite-discrete element analysis.\n \n \n \n\n\n \n Lisjak, A.; Liu, Q.; Zhao, Q.; Mahabadi, O.; and Grasselli, G.\n\n\n \n\n\n\n Geophysical Journal International, 195(1). 2013.\n \n\n\n\n
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\n\n\n@article{\n title = {Numerical simulation of acoustic emission in brittle rocks by two-dimensional finite-discrete element analysis},\n type = {article},\n year = {2013},\n keywords = {And modelling.,Fracture and flow,Geomechanics,Mechanics,Numerical solutions,Theory},\n volume = {195},\n id = {f1412d27-6f32-3244-a51b-6d515b8e8f37},\n created = {2021-02-06T07:01:17.605Z},\n file_attached = {false},\n profile_id = {4d39811a-ee39-3db8-860f-1e8ebeaaa4e2},\n last_modified = {2021-02-06T07:01:17.605Z},\n read = {false},\n starred = {false},\n authored = {true},\n confirmed = {false},\n hidden = {false},\n private_publication = {false},\n abstract = {Stress waves, known as acoustic emissions (AEs), are released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical models have been developed to simulate the deformation and damage processes of rocks, such as non-linear stress-strain behaviour and localization of failure, only a limited number have been capable of providing quantitative information regarding the associated seismicity. Moreover, the majority of these studies have adopted a pseudo-static approach based on elastic strain energy dissipation that completely disregards elastodynamic effects. This paper describes a new AE modelling technique based on the combined finite-discrete element method (FEM/DEM), a numerical tool that simulates material failure by explicitly considering fracture nucleation and propagation in the modelling domain. Given the explicit time integration scheme of the solver, stress wave propagation and the effect of radiated seismic energy can be directly captured. Quasi-dynamic seismic information is extracted from a FEM/DEM model with a newly developed algorithm based on the monitoring of internal variables (e.g. relative displacements and kinetic energy) in proximity to propagating cracks. The AE of a wing crack propagation model based on this algorithm are cross-analysed by traveltime inversion and energy estimation from seismic recordings. Results indicate a good correlation of AE initiation times and locations, and scaling of energies, independently calculated with the two methods. Finally, the modelling technique is validated by simulating a laboratory compression test on a granite sample. The micromechanical parameters of the heterogeneous model are first calibrated to reproduce the macroscopic stress-strain response measured during standard laboratory tests. Subsequently, AE frequency-magnitude statistics, spatial clustering of source locations and the evolution of AE rate are investigated. The distribution of event magnitude tends to decay as power law while the spatial distribution of sources exhibits a fractal character, in agreement with experimental observations. Moreover, the model can capture the decrease of seismic b value associated with the macrorupture of the rock sample and the transition of AE spatial distribution from diffuse, in the pre-peak stage, to strongly localized at the peak and post-peak stages, as reported in a number of published laboratory studies. In future studies, the validated FEM/DEM-AE modelling technique will be used to obtain further insights into the micromechanics of rock failure with potential applications ranging from laboratory-scale microcracking to engineering-scale processes (e.g. excavations within mines, tunnels and caverns, petroleum and geothermal reservoirs) to tectonic earthquakes triggering. © The Authors 2013 Published by Oxford University Press on behalf of The Royal Astronomical Society.},\n bibtype = {article},\n author = {Lisjak, A. and Liu, Q. and Zhao, Q. and Mahabadi, O.K. and Grasselli, G.},\n doi = {10.1093/gji/ggt221},\n journal = {Geophysical Journal International},\n number = {1}\n}\n\n Stress waves, known as acoustic emissions (AEs), are released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical models have been developed to simulate the deformation and damage processes of rocks, such as non-linear stress-strain behaviour and localization of failure, only a limited number have been capable of providing quantitative information regarding the associated seismicity. Moreover, the majority of these studies have adopted a pseudo-static approach based on elastic strain energy dissipation that completely disregards elastodynamic effects. This paper describes a new AE modelling technique based on the combined finite-discrete element method (FEM/DEM), a numerical tool that simulates material failure by explicitly considering fracture nucleation and propagation in the modelling domain. Given the explicit time integration scheme of the solver, stress wave propagation and the effect of radiated seismic energy can be directly captured. Quasi-dynamic seismic information is extracted from a FEM/DEM model with a newly developed algorithm based on the monitoring of internal variables (e.g. relative displacements and kinetic energy) in proximity to propagating cracks. The AE of a wing crack propagation model based on this algorithm are cross-analysed by traveltime inversion and energy estimation from seismic recordings. Results indicate a good correlation of AE initiation times and locations, and scaling of energies, independently calculated with the two methods. Finally, the modelling technique is validated by simulating a laboratory compression test on a granite sample. The micromechanical parameters of the heterogeneous model are first calibrated to reproduce the macroscopic stress-strain response measured during standard laboratory tests. Subsequently, AE frequency-magnitude statistics, spatial clustering of source locations and the evolution of AE rate are investigated. The distribution of event magnitude tends to decay as power law while the spatial distribution of sources exhibits a fractal character, in agreement with experimental observations. Moreover, the model can capture the decrease of seismic b value associated with the macrorupture of the rock sample and the transition of AE spatial distribution from diffuse, in the pre-peak stage, to strongly localized at the peak and post-peak stages, as reported in a number of published laboratory studies. In future studies, the validated FEM/DEM-AE modelling technique will be used to obtain further insights into the micromechanics of rock failure with potential applications ranging from laboratory-scale microcracking to engineering-scale processes (e.g. excavations within mines, tunnels and caverns, petroleum and geothermal reservoirs) to tectonic earthquakes triggering. © The Authors 2013 Published by Oxford University Press on behalf of The Royal Astronomical Society.\n
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