Publications

@article{Dadashzadeh2019,

title = {EDZ prediction and characterization for deep repository engineering based on a 2D random Voronoi grain-based modeling technique},

author = {N Dadashzadeh and MS Diederichs},

year  = {2019},

date = {2019-09-04},

urldate = {2019-09-04},

journal = {Tunnelling and Underground Space Technology},

number = {TUST_2019_1187},

keywords = {2D random Voronoi grain-based modelling, Deep geological repository (DGR), deep re, excavation damage zone (EDZ)},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{nokeyd,

title = {Calibration strategies for brittle fracture simulation at laboratory and in-situ scales using a grain-based distinct element approach},

author = {N Dadashzadeh and MS Diederichs},

year  = {2019},

date = {2019-08-24},

urldate = {2019-08-24},

journal = {Journal of Rock Mechanics and Geotechnical Engineering},

number = {JRMGE_2019_567},

keywords = {Brittle fracturing, grain-based distinct element method, Numerical simulation},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Garroux2019,

title = {EPB machine excavation of mixed soils – Laboratory characterisation},

author = {D Garroux and DGG Oliveira and M Thewes and MS Diederichs},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/geot.201900014},

doi = {https://doi.org/10.1002/geot.201900014},

year  = {2019},

date = {2019-08-01},

journal = {Geomechanics and Tunnelling},

volume = {12},

number = {4},

pages = {373-385},

abstract = {Earth pressure balance (EPB) tunnel boring machines are shield machines that rely on their own excavated material as a support medium to maintain the support pressure at the face. This material also needs to have the necessary properties to be extracted, transported and, finally, disposed of. Whenever the natural material does not fulfil the necessary requirements, additives like water, foam, polymers, and fines, must be added, modifying the excavated ground to the desired conditions. The rheological properties of any excavated material, together with any additives, must be investigated and understood, as they will influence the flow behaviour of this conditioned material, directly affecting the machine operation and tunnel logistics. While studies assessing the flowability related to the EPB excavation of sand or clay soils are available, there is a lack of information on mixed soils. This paper presents the results from a testing campaign with mixed clay-sand samples, aiming to reproduce a simplified tropical weathered mixed soil, investigating its flow behaviour when changing certain controlled variables: clay-sand proportions, clay mineral, size of the clastic grain mixed with clay, water content, and additives (foam and polymers). Results from the tests conducted with a flow table, a slump test, and a rheometer device were compared, providing insights about the flow behaviour of the tested samples and its interaction with an EPB machine.},

keywords = {Earth Pressure Balance Machine, Flow behaviour, Fluidity, mixed sand and clay soils},

pubstate = {published},

tppubtype = {article}

}

@article{nokeye,

title = {Simulation of Fragmental Rockfalls Detected Using Terrestrial Laser Scans from Rock Slopes in South-Central British Columbia, Canada},

author = {Z Sala and DJ Hutchinson and R Harrap and D Gauthier},

doi = {https://doi.org/10.5194/nhess-19-2385-2019},

year  = {2019},

date = {2019-07-25},

journal = {Natural Hazards and Earth System Sciences},

volume = {19},

pages = {2385–2404},

abstract = {Rockfall presents an ongoing challenge to the safe operation of transportation infrastructure, creating hazardous conditions which can result in damage to roads and railways, as well as loss of life. Rockfall risk assessment frameworks often involve the determination of rockfall runout in an attempt to understand the likelihood that rockfall debris will reach an element at risk. Rockfall modelling programs which simulate the trajectory of rockfall material are one method commonly used to assess potential runout. This study aims to demonstrate the effectiveness of a rockfall simulation prototype which uses the Unity 3D game engine. The technique is capable of simulating rockfall events comprised of many mobile fragments, a limitation of many industry standard rockfall modelling programs. Five fragmental rockfalls were simulated using the technique, with slope and rockfall geometries constructed from high-resolution terrestrial laser scans. Simulated change detection was produced for each of the events and compared to the actual change detection results for each rockfall as a basis for testing model performance. In each case the simulated change detection results aligned well with the actual observed change in terms of location and magnitude. An example of how the technique could be used to support the design of rockfall catchment ditches is shown. Suggestions are made for future development of the simulation technique with a focus on better informing simulated rockfall fragment size and the timing of fragmentation},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Day2019,

title = {Brittle overbreak prediction for hydrothermal complex rockmasses with healed structure},

author = {JJ Day},

doi = {10.1007/s10064-019-01578-z},

year  = {2019},

date = {2019-07-24},

journal = {Bulletin of Engineering Geology and the Environment},

volume = {79},

pages = {1041-1060(2020)},

abstract = {In massive rockmasses under high in situ and deviatoric stresses, brittle spalling is the dominant damage process and failure mode and can result in significant depths of overbreak outside the excavation design dimensions during and after construction. Significant work has been done by researchers to develop empirical and mechanistic prediction tools for brittle overbreak in homogeneous rockmasses. Brittle overbreak in heterogeneous rockmasses that contain hydrothermal veins and breccia can behave quite differently than homogeneous rockmasses, with the result that the existing tools for homogeneous rocks are inadequate. In this study, overbreak profiles and excavation observations from part of the undercut level in the New Mine Level project at the El Teniente copper–porphyry mine in Chile and intact laboratory test data from the four local rockmass units are used to develop new functions based on brittle rock mechanics to improve the prediction of the depth of brittle overbreak for similar excavations in heterogeneous rockmasses. The dacite porphyry unit, which has few stockwork veins, most closely resembles the expected homogeneous brittle overbreak development. The stockwork mafic complex unit exhibits overbreak that exceeds the homogeneous prediction because the planar, pervasive quartz veins act as crack attractors and develop maximum crack propagation after initiation and immediate strength loss. The anhydrite breccia unit and a brecciated contact zone contain large clasts of contrasting mineralogy that act as crack arresters, resulting in minimal overbreak. The proposed functions to predict depths of brittle overbreak around tunnels in these heterogeneous rocks can ultimately be used to aid in excavation and ground support design.},

keywords = {Breccia clasts, Brittle failure, Copper–molybdenum porphyry systems, Heterogeneous rockmasses, hydrothermal veins, Rockmass characterization, Tunnel overbreak prediction},

pubstate = {published},

tppubtype = {article}

}

@article{Day2019b,

title = {Composite Geological Strength Index approach with application to hydrothermal vein networks and other healed intrablock structures in complex rockmasses},

author = {JJ Day and MS Diederichs and DJ Hutchinson},

doi = {10.1007/s10706-019-00980-4},

year  = {2019},

date = {2019-06-20},

journal = {Geotechnical and Geological Engineering},

volume = {37},

pages = {5285-5314},

abstract = {Conventional rockmass characterization and analysis methods for geotechnical assessment in mining, civil tunnelling, and other excavations consider only the intact rock properties and the discrete fractures that are present and form blocks within rockmasses. As modern underground excavations go deeper and enter into more high stress environments with complex excavation geometries and associated stress paths, healed structures within initially intact rock blocks such as hydrothermal veins, veinlets and stockwork (termed intrablock structures) are having an increasing influence on rockmass behaviour and should be included in modern geotechnical engineering design. Field observations indicate the conventional Geological Strength Index (GSI) does not accurately estimate rockmass strength and behaviour of complex rockmasses. A modified GSI chart to include intrablock structures and a new Composite Geological Strength Index (CGSI) methodology to combine multiple suites of rockmass structure using a weighted harmonic average are presented as tools to evaluate complex rockmasses that contain multiple suites of structure for application to geomechanical numerical models. CGSI is introduced and numerically validated using implicit and explicit finite element method numerical simulations of an underground excavation and a case study of field observations in an adit at the El Teniente mine in Chile. In both cases, the CGSI approach using the modified GSI chart results in an improved estimate of rockmass behaviour in implicit equivalent continuum numerical models when compared to a conventional GSI approach.},

keywords = {Complex rockmasses, Composite Geological Strength Index, Finite element method numerical models, Geological Strength Index, Healed intrablock structures, Rockmass characterization},

pubstate = {published},

tppubtype = {article}

}

@article{deOliveira2019b,

title = {The Consistency Index and Its Correlation with EPB Excavation of Mixed Clay–Sand Soils},

author = {DGG Oliveira and M Thewes and MS Diederichs and MJ Lato},

url = {https://link.springer.com/article/10.1007%2Fs10706-018-0612-x},

doi = {https://doi.org/10.1007/s10706-018-0612-x},

year  = {2019},

date = {2019-06-18},

journal = {Geotechnical and Geological Engineering},

volume = {37},

pages = {327-345},

abstract = {The behavioural properties of excavated ground have significant influence on the excavation process performed by an Earth Pressure Balance Machine (EPBM), as they are among the main factors responsible for maintaining the pressure ahead of the face, which affects face stability. Therefore, understanding the characteristics of the excavated material along with its flow behaviour is essential for a successful EPB tunnel drive. In scenarios involving the excavation of fine-grained soils containing clay minerals, the consistency index has been widely used as a guideline to define the ideal state of the excavated material. However, there are certain restrictions for the use of this index, the first of which are the Atterberg limits. These limits become more restrictive when mixed soils are involved. This study presents a brief review of the application of the consistency index and Atterberg limits in order to predict the performance of an EPB excavation. This study presents the results of a laboratory testing campaign with artificially mixed clay–sand soils by using a flow table as a preliminary flow assessment of cohesive soils.},

keywords = {Atterberg limits, Consistency index, Earth Pressure Balance Machine, EPB soil conditioning, Flow table, mixed sand and clay soils},

pubstate = {published},

tppubtype = {article}

}

@article{Bonneau2019c,

title = {The Use of Terrestrial Laser Scanning for the Characterization of a Cliff-Talus System in the Thompson River Valley, British Columbia, Canada},

author = {D Bonneau and DJ Hutchinson},

doi = {10.1016/j.geomorph.2018.11.022},

year  = {2019},

date = {2019-02-15},

journal = {Geomorphology},

volume = {327},

pages = {598-609},

abstract = {A postglacial river terrace along the Thompson River in Interior British Columbia, Canada has been monitored using terrestrial laser scanning (TLS) and high-resolution photography for almost a 3-year study to observe the deformation and failure processes, which result in changes in the slope morphology. Change detection using Multiscale Model to Model Cloud Comparison (M3C2) and a multi-scale dimensionality analysis (CANUPO) were performed on the 3-dimensional point cloud data to track the deposition patterns occurring in this active cliff talus system. Changes documented in the analysis of TLS data were verified using the high-resolution photography. Over 1.5 m of valley parallel retreat was captured in a section of the cliff face related to instability of a cobble and boulder horizon beneath a thick fluvial gravel unit. Because of the high-resolution remote sensing data, it was possible to observe a longitudinal sorting of grain sizes (i.e. fall sorting) in this cliff-talus system, whereby the size of individual particles controls the position on the slope. The overall mapped distribution of particle sizes on the slope remained constant for the almost 3-year study period. Flows of granular debris were observed in TLS change detection and the CANUPO analysis was able to display the longitudinal and lateral sorting of grain sizes that occurs during flow. This case history demonstrates that high resolution remote sensing data of large slopes permits us to link the geomorphic processes occurring in the cliff face with mass movement and deposition occurring on the talus slope below.},

keywords = {CANUPO, Grain size mapping, Granular flows, Machine learning, Talus, terrestrial laser scanning},

pubstate = {published},

tppubtype = {article}

}

@article{Vazaios2019,

title = {Assessing fracturing mechanisms and evolution of excavation damaged zone of tunnels in interlocked rock masses at high stresses using a finite-discrete element approach},

author = {I Vazaios and N Vlachopoulos and MS Diederichs},

url = {https://www.sciencedirect.com/science/article/pii/S1674775518303652},

doi = {https://doi.org/10.1016/j.jrmge.2019.02.004},

issn = {1674-7755},

year  = {2019},

date = {2019-02-13},

journal = {Journal of Rock Mechanics and Geotechnical Engineering},

volume = {11},

number = {4},

pages = {701-722},

abstract = {Deep underground excavations within hard rocks can result in damage to the surrounding rock mass mostly due to redistribution of stresses. Especially within rock masses with non-persistent joints, the role of the pre-existing joints in the damage evolution around the underground opening is of critical importance as they govern the fracturing mechanisms and influence the brittle responses of these hard rock masses under highly anisotropic in situ stresses. In this study, the main focus is the impact of joint network geometry, joint strength and applied field stresses on the rock mass behaviours and the evolution of excavation induced damage due to the loss of confinement as a tunnel face advances. Analysis of such a phenomenon was conducted using the finite-discrete element method (FDEM). The numerical model is initially calibrated in order to match the behaviour of the fracture-free, massive Lac du Bonnet granite during the excavation of the Underground Research Laboratory (URL) Test Tunnel, Canada. The influence of the pre-existing joints on the rock mass response during excavation is investigated by integrating discrete fracture networks (DFNs) of various characteristics into the numerical models under varying in situ stresses. The numerical results obtained highlight the significance of the pre-existing joints on the reduction of in situ rock mass strength and its capacity for extension with both factors controlling the brittle response of the material. Furthermore, the impact of spatial distribution of natural joints on the stability of an underground excavation is discussed, as well as the potentially minor influence of joint strength on the stress induced damage within joint systems of a non-persistent nature under specific conditions. Additionally, the in situ stress-joint network interaction is examined, revealing the complex fracturing mechanisms that may lead to uncontrolled fracture propagation that compromises the overall stability of an underground excavation.},

keywords = {Brittle failure, Discrete fracture networks (DFN), excavation damage zone (EDZ), finite–discrete element method (FDEM), tunnelling},

pubstate = {published},

tppubtype = {article}

}

@article{VAZAIOS201912,

title = {Assessment of strain bursting in deep tunnelling by using the finite-discrete element method},

author = {I Vazaios and MS Diederichs and N Vlachopoulos},

url = {https://www.sciencedirect.com/science/article/pii/S167477551830163X},

doi = {https://doi.org/10.1016/j.jrmge.2018.06.007},

issn = {1674-7755},

year  = {2019},

date = {2019-02-01},

journal = {Journal of Rock Mechanics and Geotechnical Engineering},

volume = {11},

number = {1},

pages = {12-37},

abstract = {Rockbursting in deep tunnelling is a complex phenomenon posing significant challenges both at the design and construction stages of an underground excavation within hard rock masses and under high in situ stresses. While local experience, field monitoring, and informed data-rich analysis are some of the tools commonly used to manage the hazards and the associated risks, advanced numerical techniques based on discontinuum modelling have also shown potential in assisting in the assessment of rockbursting. In this study, the hybrid finite-discrete element method (FDEM) is employed to investigate the failure and fracturing processes, and the mechanisms of energy storage and rapid release resulting in bursting, as well as to assess its utility as part of the design process of underground excavations. Following the calibration of the numerical model to simulate a deep excavation in a hard, massive rock mass, discrete fracture network (DFN) geometries are integrated into the model in order to examine the impact of rock structure on rockbursting under high in situ stresses. The obtained analysis results not only highlight the importance of explicitly simulating pre-existing joints within the model, as they affect the mobilised failure mechanisms and the intensity of strain bursting phenomena, but also show how the employed joint network geometry, the field stress conditions, and their interaction influence the extent and depth of the excavation induced damage. Furthermore, a rigorous analysis of the mass and velocity of the ejected rock blocks and comparison of the obtained data with well-established semi-empirical approaches demonstrate the potential of the method to provide realistic estimates of the kinetic energy released during bursting for determining the energy support demand.},

keywords = {Brittle fracturing, Deep tunnelling, Discrete fracture networks (DFN), Finite-discrete element method (FDEM), Hard rock excavations, Rockburst},

pubstate = {published},

tppubtype = {article}

}

@article{nokeyf,

title = {Measuring the in-situ response of tunnel support using high spatial resolution optical fiber strain sensing},

author = {B Forbes and N Vlachopoulos and MS Diederichs},

year  = {2019},

date = {2019-01-01},

urldate = {2019-01-01},

journal = {International Journal of Mining Science and Technology},

keywords = {Distributed optical fiber strain sensing, In-situ response, Tunnel support},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{deOliveira2018b,

title = {EPB tunnelling through clay‐sand mixed soils: Proposed methodology for clogging evaluation},

author = {DGG Oliveira and M Thewes and MS Diederichs and L Langmaack},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/geot.201800009},

doi = {https://doi.org/10.1002/geot.201800009},

year  = {2018},

date = {2018-08-01},

journal = {Geomechanics and Tunnelling},

volume = {11},

number = {4},

pages = {375-387},

abstract = {The clogging of Tunnel Boring Machine (TBM) tools by soils has long been investigated, owing to the numerous difficulties arising in shield tunnelling as a result. Its occurrence leads to operation delays owing to the frequent and lengthy interventions required to unblock the soil stuck to the excavation tools and screw conveyor. Several authors have proposed laboratory tests for evaluating the clogging potential, however, those include limitations, such as not considering the clay fraction in a soil. One of these methods is the empirical stickiness evaluation, whereby a mixer and a beater are used to define a clogging evaluation parameter. Following an extended test campaign using soils with different clay contents and minerals, it became clear that this method was not adequate to provide reliable information regarding the tendency of a soil to clog in a tunnel drive. A new device was then implemented, which adds to the first method a kinetic energy impulse via dropping of the beater from a certain height. This combination of methods could provide a reasonable approximation of the potential for clogging to occur along Earth Pressure Balance Machine (EPB) tunnel drives. This paper presents the results of the proposed combined methodology for clogging evaluation, as well as the research evolution that led to the addition of the beater dropping stage.},

keywords = {beater dropping stage, Clogging, clogging evaluation parameter, Earth Pressure Balance Machine, empirical stickiness evaluation, mixed sand and clay soils},

pubstate = {published},

tppubtype = {article}

}

@article{deOliveira2018,

title = {Consistency Index and Its Correlation with EPB Excavation of Mixed Clay–Sand Soils},

author = {DGG Oliveira and M Thewes and MS Diederichs and L Langmaack},

doi = {10.1007/s10706-018-0612-x},

year  = {2018},

date = {2018-06-18},

journal = {Geotechnical and Geological Engineering},

volume = {37},

pages = {327-345},

abstract = {The behavioural properties of excavated ground have significant influence on the excavation process performed by an Earth Pressure Balance Machine (EPBM), as they are among the main factors responsible for maintaining the pressure ahead of the face, which affects face stability. Therefore, understanding the characteristics of the excavated material along with its flow behaviour is essential for a successful EPB tunnel drive. In scenarios involving the excavation of fine-grained soils containing clay minerals, the consistency index has been widely used as a guideline to define the ideal state of the excavated material. However, there are certain restrictions for the use of this index, the first of which are the Atterberg limits. These limits become more restrictive when mixed soils are involved. This study presents a brief review of the application of the consistency index and Atterberg limits in order to predict the performance of an EPB excavation. This study presents the results of a laboratory testing campaign with artificially mixed clay–sand soils by using a flow table as a preliminary flow assessment of cohesive soils.},

keywords = {Atterberg limits, Consistency index, Earth Pressure Balance Machine, EPB soil conditioning, Flow table, mixed sand and clay soils},

pubstate = {published},

tppubtype = {article}

}

@article{Vazaios2018b,

title = {Assessment of strain bursting in deep tunnelling by using the finite-discrete element method},

author = {I Vazaios and MS Diederichs and N Vlachopoulos},

url = {https://www.sciencedirect.com/science/article/pii/S167477551830163X},

doi = {https://doi.org/10.1016/j.jrmge.2018.06.007},

issn = {1674-7755},

year  = {2018},

date = {2018-06-10},

journal = {Journal of Rock Mechanics and Geotechnical Engineering},

volume = {11},

number = {1},

pages = {12-37},

abstract = {Rockbursting in deep tunnelling is a complex phenomenon posing significant challenges both at the design and construction stages of an underground excavation within hard rock masses and under high in situ stresses. While local experience, field monitoring, and informed data-rich analysis are some of the tools commonly used to manage the hazards and the associated risks, advanced numerical techniques based on discontinuum modelling have also shown potential in assisting in the assessment of rockbursting. In this study, the hybrid finite-discrete element method (FDEM) is employed to investigate the failure and fracturing processes, and the mechanisms of energy storage and rapid release resulting in bursting, as well as to assess its utility as part of the design process of underground excavations. Following the calibration of the numerical model to simulate a deep excavation in a hard, massive rock mass, discrete fracture network (DFN) geometries are integrated into the model in order to examine the impact of rock structure on rockbursting under high in situ stresses. The obtained analysis results not only highlight the importance of explicitly simulating pre-existing joints within the model, as they affect the mobilised failure mechanisms and the intensity of strain bursting phenomena, but also show how the employed joint network geometry, the field stress conditions, and their interaction influence the extent and depth of the excavation induced damage. Furthermore, a rigorous analysis of the mass and velocity of the ejected rock blocks and comparison of the obtained data with well-established semi-empirical approaches demonstrate the potential of the method to provide realistic estimates of the kinetic energy released during bursting for determining the energy support demand.},

keywords = {Brittle fracturing, Deep tunnelling, Discrete fracture networks (DFN), finite–discrete element method (FDEM), Hard rock excavations, Rockburst},

pubstate = {published},

tppubtype = {article}

}

@article{Vazaios2018bb,

title = {Effects of confinement on rock mass modulus: a synthetic rock mass modelling (SRM) study},

author = {I Vazaios and K Farahmand and N Vlachopoulos and MS Diederichs},

url = {https://www.sciencedirect.com/science/article/pii/S1674775517302044},

doi = {https://doi.org/10.1016/j.jrmge.2018.01.002},

issn = {1674-7755},

year  = {2018},

date = {2018-06-01},

journal = {Journal of Rock Mechanics and Geotechnical Engineering},

volume = {10},

number = {3},

pages = {436-456},

abstract = {The main objective of this paper is to examine the influence of the applied confining stress on the rock mass modulus of moderately jointed rocks (well interlocked undisturbed rock mass with blocks formed by three or less intersecting joints). A synthetic rock mass modelling (SRM) approach is employed to determine the mechanical properties of the rock mass. In this approach, the intact body of rock is represented by the discrete element method (DEM)-Voronoi grains with the ability of simulating the initiation and propagation of microcracks within the intact part of the model. The geometry of the pre-existing joints is generated by employing discrete fracture network (DFN) modelling based on field joint data collected from the Brockville Tunnel using LiDAR scanning. The geometrical characteristics of the simulated joints at a representative sample size are first validated against the field data, and then used to measure the rock quality designation (RQD), joint spacing, areal fracture intensity (P21), and block volumes. These geometrical quantities are used to quantitatively determine a representative range of the geological strength index (GSI). The results show that estimating the GSI using the RQD tends to make a closer estimate of the degree of blockiness that leads to GSI values corresponding to those obtained from direct visual observations of the rock mass conditions in the field. The use of joint spacing and block volume in order to quantify the GSI value range for the studied rock mass suggests a lower range compared to that evaluated in situ. Based on numerical modelling results and laboratory data of rock testing reported in the literature, a semi-empirical equation is proposed that relates the rock mass modulus to confinement as a function of the areal fracture intensity and joint stiffness.},

keywords = {Composite Geological Strength Index, Confinement, Discrete fracture networks (DFN), Rockmass modulus, Synthetic rockmass modelling (SRM)},

pubstate = {published},

tppubtype = {article}

}

@article{Vazaios2018,

title = {Mechanical analysis and interpretation of excavation damage zone formation around deep tunnels within massive rock masses using hybrid finite–discrete element approach: case of Atomic Energy of Canada Limited (AECL) Underground Research Laboratory (URL) test tunnel},

author = {I Vazaios and N Vlachopoulos and MS Diederichs},

doi = {10.1139/cgj-2017-0578},

year  = {2018},

date = {2018-04-19},

journal = {Canadian Geotechnical Journal},

volume = {56},

number = {1},

pages = {35-59},

abstract = {The construction of an underground opening leads to changes in the in situ stress regime surrounding the excavation. The opening influences the rock mass owing to the redistribution of the stresses and results in the disturbance of the surrounding ground. At great depths, massive to slightly or moderately fractured rock masses are usually encountered, and under high stresses, they are more likely to behave in a brittle manner during an excavation. While constitutive models have been developed and proposed for the numerical simulation of such excavations using continuum mechanics, this brittle response cannot be simulated accurately enough, since the material behaviour is governed by fracture initiation and propagation. On the contrary, discontinuum approaches are more suitable in such cases. For the purposes of this paper, the brittle behaviour of hard, massive rock masses and the associated spalling failure mechanisms were simulated by employing a finite–discrete element method (FDEM) approach using Irazu software. The generated numerical model was utilized to replicate field conditions based on the observations at the Atomic Energy of Canada Limited (AECL) Underground Research Laboratory (URL) test tunnel located in Pinawa, Manitoba, Canada. The model results are compared with field observation data to explicitly demonstrate the suitability of the method.},

keywords = {Brittle failure, excavation damage zone (EDZ), finite–discrete element method (FDEM), spalling, tunnelling},

pubstate = {published},

tppubtype = {article}

}

@article{WALTON2018172,

title = {Change detection in drill and blast tunnels from point cloud data},

author = {G Walton and MS Diederichs and K Weinhardt and D Delaloyle and MJ Lato and A Punkkinen},

url = {https://www.sciencedirect.com/science/article/pii/S1365160918302430},

doi = {10.1016/j.ijrmms.2018.03.004},

issn = {1365-1609},

year  = {2018},

date = {2018-03-13},

journal = {International Journal of Rock Mechanics and Mining Sciences},

volume = {105},

pages = {172-181},

abstract = {During the excavation of underground workings, stress redistribution around the excavation causes the rockmass to deform. The magnitude of this deformation depends on the rockmass conditions, the magnitude, orientation, and anisotropy of the in situ stresses, the excavation method and rate, and the type and location of installed support. Monitoring data which records the deformation of an excavation over time can therefore be used to back analyze information about the rockmass parameters and/or stress state, and can serve as an early warning for more severe failures1. 

 

With the recent profileration of laser scanning technology (and photogrammetry) in geotechnical engineering applications, it is natural that some researchers have begun to study its potential use as a deformation monitoring tool in excavations. By comparing two time-separated point cloud data sets (or attributes of these data sets), rockmass deformation can be mapped. This deformation can be mapped as either relative or absolute. To obtain absolute deformation measurements, georeferencing must be employed. This typically means that the location of the scanner must be surveyed from a known absolute reference for each instance of data collection using a total station. The advantage of absolute positioning when recording deformations is that translations of individual tunnels due to nearby excavation activities can be recorded; in contrast, only closure measurements can be obtained when using relative positioning2. The practical advantage of using relative positioning is that it requires much less time to set up scans, meaning that in an active excavation environment, typical cycle times can be maintained3. 

 

With the exception of closest point approaches, methods for comparing time-separated point cloud data sets have generally used what we refer to as a “global fitting approach”. The global fitting approach for change detection depends on the comparison of 2D or 3D shapes fit to two data sets taken at the same location. Since only a small number of parameters are required to derive the best-fit shape as compared to the large number of data points, anomalous results and random errors can be effectively removed from the analysis. By contrast, algorithms based on closest point distance are significantly influenced by the range error inherent in the instruments used4. 

 

Delaloye5 provides a framework for the comparison of point cloud data sets collected in elliptical excavations (see Walton et al.3 and Delaloye et al.6 for further developments). When fitting an ellipse to data, the long and short axes of the ellipse correspond to the principal deformation directions within the tunnel. To calculate the amount of normalized tunnel convergence, uniform deformation between measurements must be assumed. The orientation of the ellipse can easily be calculated, and is important to identify because a change in the orientation of the ellipse suggests a change in the deformation pattern. 

 

Whereas previous works have focused on excavations with simple geometries (e.g. Wannanmacher et al.7, Nuttens et al.8), this study uses data from the Creighton Mine in Sudbury, Canada to investigate the applicability of various change detection methods for application in an excavation with irregular geometry.},

keywords = {change detection, Laser scanning, LiDAR, Mining, tunnelling},

pubstate = {published},

tppubtype = {article}

}

@article{FARAHMAND2018162,

title = {Investigating the scale-dependency of the geometrical and mechanical properties of a moderately jointed rock using a synthetic rock mass (SRM) approach},

author = {K Farahmand and I Vazaios and MS Diederichs and N Vlachopoulos},

url = {https://www.sciencedirect.com/science/article/pii/S0266352X17302677v},

doi = {https://doi.org/10.1016/j.compgeo.2017.10.002},

issn = {0266-352X},

year  = {2018},

date = {2018-03-01},

journal = {Computers and Geotechnics},

volume = {95},

pages = {162-179},

abstract = {A synthetic rock mass (SRM) model coupling discrete fracture networks (DFNs) and a discrete element grain-based model (DEM) is used to characterize the mechanical properties of moderately jointed rockmasses under confined and unconfined conditions. The scale dependency of the rockmass properties is investigated using the concept of representative element volume (REV). The numerical results are compared with the estimated values from empirical methods. It is determined that the empirical Hoek-Brown criterion correctly estimates the unconfined strength of the rockmass with non-persistent joints, while it overestimates the strength under confined conditions. An S-shaped strength envelope is obtained from the numerical results.},

keywords = {Deformability, Discrete fracture networks (DFN), LiDAR, Representative elementary volume (REV), Rockmass strength, Scale-dependency, Synthetic rockmass (SRM)},

pubstate = {published},

tppubtype = {article}

}

@article{Diederichs2018,

title = {Early assessment of dynamic rupture hazard for rockburst risk management in deep tunnel projects},

author = {MS Diederichs},

url = {http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2225-62532018000300004},

doi = {http://dx.doi.org/10.17159/2411-9717/2018/v118n3a1},

issn = {2225-6253},

year  = {2018},

date = {2018-03-01},

journal = {Journal of the Southern African Institute of Mining and Metallurgy},

volume = {118},

number = {3},

pages = {193-204},

abstract = {Managing rockbursting conditions in mine development and operational environments is a complex and difficult challenge. The hazard and the associated risks can be managed based on local experience, monitoring, and informed data-rich analysis. On the other hand, blind development for deep tunnelling is being carried out around the world at depths in excess of 2 km and rockbursting has become a common and serious challenge. The rockburst mechanism is predominantly tunnelling-induced dynamic rupture or strain bursting, distinct from the remote or mine-generated events that impact mining excavations. Considerations of rock petrology, fabric, mechanical parameters, and structure allow an estimate of brittle response. The potential for energy storage and rapid release must be accounted for in order to understand the burst potential early in the basic design stage for deep tunnels. Failure to do so can result in unsafe conditions and years of delay. In this paper a multistep semi-empirical approach for early assessment of strain burst or dynamic rupture potential along deep tunnel alignments in variable ground is presented.},

keywords = {dynamic rupture, hazard assessment, High stress, risk management, Rockburst, tunnelling},

pubstate = {published},

tppubtype = {article}

}

@article{Ghazvinian2018,

title = {Progress of brittle microfracturing in crystalline rocks under cyclic loading conditions},

author = {E Ghazvinian and MS Diederichs},

doi = {http://dx.doi.org/10.17159/2411-9717/2018/v118n3a4},

issn = {2411-9717},

year  = {2018},

date = {2018-03-01},

journal = {Journal of the Southern African Institute of Mining and Metallurgy},

volume = {118},

number = {3},

pages = {217-226},

abstract = {The stress at onset of yielding for the walls of deep underground excavations in hard rock is significantly less than the laboratory strength of intact rock samples. The wall stability is rather controlled by the microfracturing strength of the rock (i.e. crack propagation (CD) and initiation (CI) thresholds). Factors such as loading and unloading effect of excavation, glaciation, stress rotation in front of a tunnel face, etc. can contribute to the progressive damage of the rock, influencing the CI and CD thresholds and therefore contributing to the damage intensity around underground openings. The effect of stress rotation and stress fatigue on crack damage thresholds is systematically investigated in this paper through state-of-the-art laboratory testing and monitoring techniques in combination with advanced grain-based numerical modelling.},

keywords = {brittle microfracturing, Crack initiation, crack propogation, cyclic loading},

pubstate = {published},

tppubtype = {article}

}

@article{Packulak2018,

title = {Role of rock direct shear testing in determining geomechanical properties of fractures},

author = {TR Packulak and JJ Day and MS Diederichs},

year  = {2018},

date = {2018-03-01},

journal = {Tunnels and Tunnelling},

volume = {2},

pages = {32-36},

abstract = {Rockmass discontinuities regularly govern the material behaviour around engineering projects such as natural slopes, surface excavations, and underground openings. Geotechnical laboratory tests, such as direct shear, provide a means to determine stiffness, strength, and post-peak material properties, which are key parameters used to quantify rockmass behaviour. Direct shear tests are typically conducted under constant normal stress (CNL*) and constant normal load (CNL) boundary conditions, which are considered to represent fracture behaviour in near surface gravity-driven environments. Both CNL and CNL* conditions allow the fracture to dilate freely during shear, so there is no feedback between dilation and normal stress. A third boundary condition option in direct shear testing is constant normal stiffness (CNS), which is considered to better reflect behaviours of rock fractures near underground excavations, such as tunnels, mines, and nuclear waste repositories. Assessing geomechanical properties of fractures in granitic rock under CNL* and CNS boundary conditions is the focus of this investigation.},

keywords = {Direct shear testing, Discontinuity, Heterogeneous rockmasses, Rockmass},

pubstate = {published},

tppubtype = {article}

}

@article{Oke2018,

title = {Improvement to the Convergence-Confinement Method: Inclusion of Support Installation Proximity and Stiffness},

author = {J Oke and N Vlachopoulos and MS Diederichs},

doi = {10.1007/s00603-018-1418-0},

year  = {2018},

date = {2018-02-01},

journal = {Rock Mechanics and Rock Engineering},

volume = {51},

pages = {1495-1519},

abstract = {The convergence-confinement method (CCM) is a method that has been introduced in tunnel construction that considers the ground response to the advancing tunnel face and the interaction with installed support. One limitation of the CCM is due to the numerically or empirically driven nature of the longitudinal displacement profile and the incomplete consideration of the longitudinal arching effect that occurs during tunnelling operations as part of the face effect. In this paper, the authors address the issue associated with when the CCM is used within squeezing ground conditions at depth. Based on numerical analysis, the authors have proposed a methodology and solution to improving the CCM in order to allow for more accurate results for squeezing ground conditions for three different excavation cases involving various excavation-support increments and distances from the face to the supported front. The tunnelling methods of consideration include: tunnel boring machine, mechanical (conventional), and drill and blast.},

keywords = {Analytical, Convergence-confinement, Numerical modelling, Support, tunnelling},

pubstate = {published},

tppubtype = {article}

}

@article{Paraskevopoulou2018,

title = {Analysis of time-dependent deformation in tunnels using the Convergence-Confinement Method},

author = {C Paraskevopoulou and MS Diederichs},

doi = {10.1016/j.tust.2017.07.001},

year  = {2018},

date = {2018-01-01},

journal = {Tunnelling and Underground Space Technology},

volume = {71},

pages = {62-80},

abstract = {During the excavation of a tunnel the accumulated wall displacement and the loading of tunnel support is the result of both the tunnel advance (round length and cycle time) and the time-dependent behaviour of the surrounding rock mass. The current approach to analyze the tunnel wall displacement increase is based on the Convergence-Confinement Method (CCM) performed with either analytical (closed form solutions) or the usage of the Longitudinal Displacement Profiles. This approach neglects the influence of time-dependency resulting in delayed deformation that may manifest even minutes or hours after excavation. Failure to consider the added displacements in the preliminary design can result in false selecting the time of installation and the type of support system causing safety issues to the working personnel, leading to cost overruns and project delivery delays. This study focuses on investigating and analyzing the total displacements around a circular tunnel in a visco-elastic medium by performing an isotropic axisymmetric finite difference modelling, proposing a new yet simplified approach that practitioners can use taking into account the effect of time.},

keywords = {Creep, Long-term behaviour, Time-dependency, Visco-elastic parameters},

pubstate = {published},

tppubtype = {article}

}

@article{Day2017,

title = {New direct shear testing protocols and analyses for fractures and healed intrablock rockmass discontinuities},

author = {JJ Day and MS Diederichs and DJ Hutchinson},

doi = {10.1016/j.enggeo.2017.08.027},

year  = {2017},

date = {2017-11-07},

journal = {Engineering Geology},

volume = {229},

pages = {53-72},

abstract = {Modern geotechnical numerical design is limited by conventional characterization and data collection practices, which do not capture detailed parameters of intact rock and rockmass structure that are necessary for input to sophisticated and powerful simulation tools. Furthermore, as modern underground excavations go deeper and enter into more high stress environments with complex excavation geometries and associated stress paths, healed structures within initially intact rock blocks such as sedimentary nodules and hydrothermal veins (termed intrablock structure, where conventional fractures are termed interblock structure) are having an increasing influence on rockmass behaviour and should be included in modern geotechnical design. The role of sedimentary nodular intrablock structure in the Cobourg limestone on rockmass behaviour is an important consideration for the design of Canadian Deep Geological Repositories (DGRs) for the permanent storage of nuclear waste. This direct shear test program provides valuable laboratory data results for mechanical properties of targeted fracture surfaces and intrablock features in the Cobourg limestone for application to the numerical geotechnical design of prospective DGRs. Measurements of normal stiffness (Kn), shear stiffness (Ks), shear strength (in terms of cohesion (c) and friction angle (ϕ) from the Mohr-Coulomb shear strength criterion), and initial dilation angle (ψ) parameters are assessed and critically evaluated. These established parameters for fractures are applied to the tests on intrablock structures to provide a consistent basis for comparison and to enable the use of existing mechanical parameters in numerical model inputs. The implications of normal and shear stiffness property selection are evaluated at the excavation scale using finite element models with explicit rockmass structure. The critical analyses of conventional calculations of parameters results in improved calculation methods with mechanistic reasoning for the ultimate application of the data to sophisticated numerical models with explicit or discrete rockmass structure.},

keywords = {Cobourg limestone, Direct shear testing, Healed (intrablock) structure, Normal stiffness, Shear stiffness, Shear strength},

pubstate = {published},

tppubtype = {article}

}

@article{Diederichs2017bb,

title = {An overview of geomechanics field-based training in Europe},

author = {MS Diederichs},

year  = {2017},

date = {2017-11-01},

journal = {Tunnels and Tunnelling},

volume = {6},

pages = {30-33},

keywords = {Field-based training, geomechanics},

pubstate = {published},

tppubtype = {article}

}

@article{Paraskevopoulou2017,

title = {Time-dependent behaviour of brittle rocks based on static load laboratory tests},

author = {C Paraskevopoulou and MA Perras and MS Diederichs and S Loew and T Lam and M Jensen},

url = {https://link.springer.com/article/10.1007/s10706-017-0331-8},

doi = {https://doi.org/10.1007/s10706-017-0331-8},

year  = {2017},

date = {2017-08-22},

journal = {Geotechnical and Geological Engineering},

volume = {36},

pages = {337-376},

abstract = {Cumulative elastic and inelastic strain and associated internal stress changes as well as damage evolution over time in brittle rocks control the long-term evolution of the rockmass around underground openings or the land surface settlement. This long-term behaviour is associated with time-dependent deformation and is commonly investigated under static load (creep) conditions in laboratory scale. In this study, low Jurassic and Cobourg limestone samples were tested at different static load levels in unconfined conditions to examine the time to failure. Comparisons are made with longterm testing data in granites and limestones associated with the Canadian nuclear waste program and other data from the literature. Failure typically occurred within the time limits of the test program (4 months) with axial (differential) stress levels near or above the crack damage threshold (CD) estimated from baseline testing. The results also suggest that the time to failure of limestone is longer than that of granite at a given driving stress. Further insight into samples that did not reach failure was investigated and it was found that there was a clear division between failure and no failure samples based on the Maxwell viscosity of the samples tested (indicating that viscosity changes near the yield threshold of these rocks. Furthermore, samples showed a clear tendency towards failure within minutes to hours when loaded above CD and no failure was shown for samples loaded below CI (crack initiation threshold). Samples loaded between CD and CI show a region of uncertainty, with some failing and other not at similar driving stress-ratios. Although such testing is demanding in terms of setup, control of conditions, continuous utilization of test and data acquisition equipment and data processing, it yields important information about the long-term behaviour of brittle rocks, such as the expect time to failure and the visco-elastic behaviour. The information presented in this paper can be utilized for preliminary numerical studies to gain an understanding of potential impact of long-term deformations.},

keywords = {Creep, Laboratory testing, Long-term behaviour, Static load testing, Time-dependency, Visco-elastic parameters},

pubstate = {published},

tppubtype = {article}

}

@article{Forbes2017,

title = {A new optical sensing technique for monitoring shear of rock bolts. Tunnelling and Underground Space Technology},

author = {B Forbes and N Vlachopoulos and A Hyett and MS Diederichs},

url = {https://www.sciencedirect.com/science/article/pii/S0886779816307313},

doi = {https://doi.org/10.1016/j.tust.2017.03.007},

isbn = {0886-7798},

year  = {2017},

date = {2017-06-21},

journal = {Tunnelling and Underground Space Technology},

volume = {66},

pages = {34-46},

abstract = {In addressing limitations of conventional ground support measurement, a novel optical strain sensing technique is presented that is capable of measuring strain at increments as low as 0.65mm along the entirety of an optical sensor affixed to a support element. The technique considers monitoring three sensing lengths along the profile of a fully grouted rock bolt element using a single optical fiber, which, in turn, allows the derivation of both the principle strain and principle strain direction along the bolt. A series of three experiments, which include: symmetric bending, combined axial load and bending, and double shear loading are presented and highlight the potential of the technique to capture bolt behaviour under such generalized rock bolt loading conditions. Analogized as a distributed strain rosette, the optical technique can distinguish both the coaxial and bending induced constituents of the total strain in the bolt regardless of load orientation.},

keywords = {Instrumentation, Optical sensing, Physical testing, Rock bolt, Shear, Strain analysis},

pubstate = {published},

tppubtype = {article}

}