Publications

@article{Oke2016136,

title = {Semi-Analytical Model for Umbrella Arch Systems in Squeezing Conditions},

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

url = {https://www.sciencedirect.com/science/article/pii/S0886779816301559},

doi = {https://doi.org/10.1016/j.tust.2016.03.006},

isbn = {0886-7798},

year  = {2016},

date = {2016-06-01},

journal = {Tunnelling and Underground Space Technology},

volume = {56},

pages = {136-156},

abstract = {Methods of approximation that predict the mechanical responses of the tunnel support systems in conjunction with ground behaviour are invaluable to the tunnel design engineer. Analytical models are often used in order to predict and/or validate ground-support behaviour. Conventionally, these analytical models do not account for the complex loading and reacting conditions of umbrella arch support systems throughout the tunnel excavation and support sequence. As such, a semi-analytical model is proposed within this paper for umbrella-arch systems that employ an umbrella ache with forepoles, in squeezing-ground conditions. The semi-analytical model is based on an assortment of applicable methods and theories depending on the relevant loading. Beam theory, elastic foundation theory, and the Convergence-Confinement Method (CCM) are all incorporated within the proposed analytical method. After a review of the literature it became apparent that a limited amount of models existed for squeezing-ground conditions. Previous models were based on gravity-driven (Silo Theory) loading conditions rather than the more applicable stress-driven (squeezing) loading conditions. The results of the semi-analytical approach included herein were able to reasonably capture the displacement profiles associated with captured field data. This semi-analytical approach can be considered for use by tunnel design engineers in order to aid them with tunnel support design.},

keywords = {Analytical model, Convergence-confinement method, Forepole, Numerical modelling, Umbrella arch},

pubstate = {published},

tppubtype = {article}

}

@article{Walton2016,

title = {Back analysis of a pillar monitoring experiment at 2.4 km depth in the Sudbury Basin, Canada},

author = {G Walton and MS Diederichs and A Punkkinen and J Whitmore},

url = {https://www.sciencedirect.com/science/article/pii/S1365160916300284},

doi = {https://doi.org/10.1016/j.ijrmms.2016.03.001},

issn = {1365-1609},

year  = {2016},

date = {2016-05-01},

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

volume = {85},

pages = {33-51},

abstract = {In November 2013, a pillar monitoring and back analysis experiment was initiated on the 7910 level of the Creighton Mine, in Sudbury, Canada. An extensometer array was installed horizontally through the pillar to allow zones of brittle spalling damage and dilatancy in the granitic rockmass to be identified. To aid in the interpretation of the in-situ data, laboratory data were analyzed and a calibrated three-dimensional finite-difference model of the mining area was developed. Based on an interpretation of the available data and models, it was determined that following the onset of yield, pillar cohesion degrades more rapidly than pillar frictional strength increases. The overall rockmass strength remains relatively unchanged, however, due to dilation-induced confining stress increases. As the primary dilatancy of the pillar begins to decay and the pillar walls expand, the confinement in the pillar drops. This is followed by an increase in the vertical load sustained by the pillar as the effects of mobilizing friction strength begins to dominate the rockmass behavior. The relationships demonstrated between dilatancy, strength evolution, and stress path, have significant implications for support design and understanding rockburst mechanisms.},

keywords = {Back analysis, Deep mining, Dilatancy, pillar strength},

pubstate = {published},

tppubtype = {article}

}

@article{Langford2016147,

title = {Revisiting support optimization at the Driskos tunnel using a quantitative risk approach},

author = {JC Langford and N Vlachopoulos and MS Diederichs},

url = {https://www.sciencedirect.com/science/article/pii/S1674775515001390},

doi = {https://doi.org/10.1016/j.jrmge.2015.11.003},

issn = {1674-7755},

year  = {2016},

date = {2016-04-01},

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

volume = {8},

number = {2},

pages = {147-163},

abstract = {With the scale and cost of geotechnical engineering projects increasing rapidly over the past few decades, there is a clear need for the careful consideration of calculated risks in design. While risk is typically dealt with subjectively through the use of conservative design parameters, with the advent of reliability-based methods, this no longer needs to be the case. Instead, a quantitative risk approach can be considered that incorporates uncertainty in ground conditions directly into the design process to determine the variable ground response and support loads. This allows for the optimization of support on the basis of both worker safety and economic risk. This paper presents the application of such an approach to review the design of the initial lining system along a section of the Driskos twin tunnels as part of the Egnatia Odos highway in northern Greece. Along this section of tunnel, weak rock masses were encountered as well as high in situ stress conditions, which led to excessive deformations and failure of the as built temporary support. Monitoring data were used to validate the rock mass parameters selected in this area and a risk approach was used to determine, in hindsight, the most appropriate support category with respect to the cost of installation and expected cost of failure. Different construction sequences were also considered in the context of both convenience and risk cost.},

keywords = {Driskos tunnel, Flysch, Quantitative risk analysis, Reliability-based design, Rockmass characterization, Underground support},

pubstate = {published},

tppubtype = {article}

}

@article{Diederichs201640,

title = {Thinking Geo: The Role of Geological Engineering Education in Modern Tunnelling},

author = {MS Diederichs},

year  = {2016},

date = {2016-01-01},

journal = {Tunnels and Tunnelling},

volume = {6},

pages = {40-43},

keywords = {Education, Geological Engineering, tunnelling},

pubstate = {published},

tppubtype = {article}

}

@article{Perras2015,

title = {Predicting excavation damage zone depths in brittle rocks},

author = {MA Perras and MS Diederichs},

url = {https://www.sciencedirect.com/science/article/pii/S1674775515001407},

doi = {https://doi.org/10.1016/j.jrmge.2015.11.004},

issn = {1674-7755},

year  = {2015},

date = {2015-11-30},

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

volume = {8},

number = {1},

pages = {60-74},

abstract = {During the construction of an underground excavation, damage occurs in the surrounding rock mass due in large part to stress changes. While the predicted damage extent impacts profile selection and support design, the depth of damage is a critical aspect for the design of permeability sensitive excavations, such as a deep geological repository (DGR) for nuclear waste. Review of literature regarding the depth of excavation damage zones (EDZs) indicates three zones are common and typically related to stress induced damage. Based on past developments related to brittle damage prediction using continuum modelling, the depth of the EDZs has been examined numerically. One method to capture stress induced damage in conventional engineering software is the damage initiation and spalling limit (DISL) approach. The variability of depths predicted using the DISL approach has been evaluated and guidelines are suggested for determining the depth of the EDZs around circular excavations in brittle rock masses. Of the inputs evaluated, it was found that the tensile strength produces the greatest variation in the depth of the EDZs. The results were evaluated statistically to determine the best fit relation between the model inputs and the depth of the EDZs. The best correlation and least variation were found for the outer EDZ and the highly damaged zone (HDZ) showed the greatest variation. Predictive equations for different EDZs have been suggested and the maximum numerical EDZ depths, represented by the 68% prediction interval, agreed well with the empirical evidence. This suggests that the numerical limits can be used for preliminary depth prediction of the EDZs in brittle rock for circular excavations.},

keywords = {Damage initiation and spalling limit (DISL), Deep geological repository (DGR), Empirical depth prediction, excavation damage zone (EDZ), Numerical depth prediction},

pubstate = {published},

tppubtype = {article}

}

@article{Day2015414,

title = {Effects of structural contact stiffness on strength and progressive failure of fractures and healed structure},

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

url = {https://onlinelibrary.wiley.com/doi/10.1002/geot.201500027},

doi = {https://doi.org/10.1002/geot.201500027},

year  = {2015},

date = {2015-10-01},

journal = {Geomechanics and Tunnelling},

volume = {8},

number = {5},

pages = {414-420},

abstract = {Geotechnical analysis for underground excavation design in complex tectonic environments requires an increased understanding and more rigorous consideration of the impact of healed or "intrablock" structure, such as veins, on rockmass behaviour. Intrablock structure occurs between blocks of rock defined and bounded by "interblock structure", the network of joints and other fractures conventionally considered in classic rockmass characterization, classification or rockmass property estimation. Discrete simulation of fractures has become a more commonplace model analysis technique for excavations in jointed rockmasses. Here too, however, special attention is required to simulate intrablock structure within the model. In particular, the selection and evolution of stiffness and strength values for the model discontinuity elements must follow a different logic than that adopted for fractures and true joints. A new concept to better represent the behaviour of intrablock structure in explicit numerical models is proposed and tested in this paper by means of finite element method (FEM) analysis and case study data from a 1, 200 m deep drift. This approach changes the stiffness and strength values of failed intrablock structural elements between pre-peak ("primary"), post-peak ("secondary"), and ultimate ("tertiary") states. The FEM models in the tertiary state match 96 % of overbreak patterns along the case drift, versus 80 % in primary state models. These findings suggest that the proposed method is a good option to more accurately model the influence of intrablock structure on rockmass behaviour.},

keywords = {Discrete numerical modelling, engineering geology, numerical methods, progressive yield, rock mechanics, stiffness properties},

pubstate = {published},

tppubtype = {article}

}

@article{Day2015,

title = {Optimization of structural contact stiffness and strength for discrete simulation of progressive failure of healed structure},

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

doi = {10.1002/geot.201500027},

year  = {2015},

date = {2015-10-01},

journal = {Geomechanics and Tunnelling},

volume = {8},

number = {5},

pages = {414-420},

abstract = {Geotechnical analysis for underground excavation design in complex tectonic environments requires an increased understanding and more rigorous consideration of the impact of healed or "intrablock" structure, such as veins, on rockmass behaviour. Intrablock structure occurs between blocks of rock defined and bounded by "interblock structure", the network of joints and other fractures conventionally considered in classic rockmass characterization, classification or rockmass property estimation. Discrete simulation of fractures has become a more commonplace model analysis technique for excavations in jointed rockmasses. Here too, however, special attention is required to simulate intrablock structure within the model. In particular, the selection and evolution of stiffness and strength values for the model discontinuity elements must follow a different logic than that adopted for fractures and true joints. A new concept to better represent the behaviour of intrablock structure in explicit numerical models is proposed and tested in this paper by means of finite element method (FEM) analysis and case study data from a 1, 200 m deep drift. This approach changes the stiffness and strength values of failed intrablock structural elements between pre‐peak ("primary"), post‐peak ("secondary"), and ultimate ("tertiary") states. The FEM models in the tertiary state match 96 % of overbreak patterns along the case drift, versus 80 % in primary state models. These findings suggest that the proposed method is a good option to more accurately model the influence of intrablock structure on rockmass behaviour.},

keywords = {Discrete numerical modelling, engineering geology, numerical methods, progressive yield, rock mechanics, stiffness properties},

pubstate = {published},

tppubtype = {article}

}

@article{Walton2015441,

title = {The influence of constitutive model selection on predicted stresses and yield in deep mine pillars – A case study at the Creighton mine, Sudbury, Canada},

author = {G Walton and MS Diederichs and A Punkkinen},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/geot.201500023},

doi = {https://doi.org/10.1002/geot.201500023},

year  = {2015},

date = {2015-10-01},

journal = {Geomechanics and Tunnelling},

volume = {8},

number = {5},

pages = {441-449},

abstract = {Based on recent advances in modelling the post-yield behaviour of brittle rock, the authors have developed a calibrated inelastic model of the 7,910 level (2.4 km depth) at the Creighton Mine in Sudbury, Ontario, Canada using data collected from the monitoring of pillar dilatancy. While this calibrated model represents a state-of-the-art continuum approach for capturing the progressive development of yield and stresses in mine pillars, alternative state-of-practice approaches (elastic and perfectly plastic material models, for example) represent potentially acceptable options for practical application. 

 

The purpose of this study is to examine the influence of constitutive model choice on stress paths throughout the pillar system at the mining level of interest. The strengths and limitations of various material models are compared and contrasted. Elastic models are shown to adequately represent the larger scale pillar system behaviour from a stress transfer perspective, whereas the state-of-art brittle modelling approach is shown to be ideal for understanding specific pillar-scale stresses and yield.},

keywords = {Back analysis, Deep mining, Dilatancy, Numerical modelling, pillar strength, rock mechanics},

pubstate = {published},

tppubtype = {article}

}

@article{Ghazvinian20151409,

title = {An investigation on the fabric type dependency of crack damage thresholds in brittle rocks},

author = {E Ghazvinian and MS Diederichs and D Labrie and CD Martin},

doi = {https://doi.org/10.1007/s10706-015-9909-1},

year  = {2015},

date = {2015-07-28},

journal = {Geotechnical and Geological Engineering},

volume = {33},

number = {6},

pages = {1409-1429},

abstract = {Fabric-guided micro-fracturing phenomenon in brittle rocks and its effect on crack damage thresholds remains subject to continuing research. The available fabric in rocks can act as a motivator for nucleation and/or extension and interaction of micro-fractures in a preferred orientation, or as a suppressor for growth of micro-cracks in a given direction by different mechanisms such as compliance (stiffness contrast) or preferred orientation of minerals and their boundaries. While anisotropy of brittle rocks in terms of their mechanical strengths can play a significant role in the stability of underground openings, the understanding of the dependency of crack initiation (CI) and crack propagation (CD) thresholds on the available fabric in rocks can improve predictions of the extension and density of micro-fracturing in different directions in the walls of underground openings. To better understand the fabric-guided micro-fracturing phenomenon, and also to study the effect of fabric types available in brittle rocks on their anisotropic behaviour, four types of brittle rocks with different types of fabric are investigated in terms of crack damage anisotropy in this paper. The rocks that are chosen for this study are limestone from the Cobourg Formation, Queenston shale, Olkiluoto mica gneiss and Lac du Bonnet granite. For each rock type, CI and CD thresholds are identified from the unconfined compressive strength testing data. The mechanical behaviour of the four rock types are investigated at each damage stress level and the contributing factors to the isotropic or anisotropic behaviour of the rocks at different crack damage thresholds are discussed.},

keywords = {Anisotropy, Brittle rocks, Crack initiation, crack propagation, Fabric-guided micro-fracturing, rock mechanics},

pubstate = {published},

tppubtype = {article}

}

@article{Walton201598,

title = {A mine shaft case study on the accurate prediction of yield and displacements in stressed ground using lab-derived material properties},

author = {G Walton and MS Diederichs},

doi = {https://doi.org/10.1016/j.tust.2015.04.010},

issn = {0886-7798},

year  = {2015},

date = {2015-06-01},

journal = {Tunnelling and Underground Space Technology},

volume = {49},

pages = {98-113},

abstract = {Continuum models provide a useful tool for the prediction of stress re-distribution due to excavation and induced yielding, and are used as a key analysis tool in the design of many underground excavations. Recent developments in the study of rock strength and post-yield behaviour have played a key role in improving our understanding of how plastic constitutive models can also be used to practically replicate observed phenomena in brittle rocks. In particular, new models for rock dilatancy can help to improve the applicability of plastic constitutive models as a predictive tool for excavation design. In this study, laboratory data for a heterogeneous, brittle, conglomerate unit from a mine shaft has been analysed. Using parameters from this analysis, brittle strength and dilatancy models have been implemented in a finite-difference code to predict not only stress re-distribution and yield around the shaft, but also to obtain realistic displacement values. Comparison of the modelling results to displacements measured using borehole extensometers show that the constitutive model and lab-derived parameters used were effective in predicting the rockmass behaviour. Parameters were further optimized through back analysis. One interesting finding of this analysis is that the in-situ rockmass dilation decay rate (as a function of plastic strain) appears to be faster than estimated based on laboratory data, which may be indicative of the influence of rockmass-scale natural fractures and other geological structures on the dilation decay process. It also appears possible to model the in-situ dilation decay rate using a single parameter, instead of separate parameters for unconfined and confined conditions. To conclude the study, more numerical results obtained using alternative dilatancy models are presented to illustrate the problem of non-uniqueness in plasticity back analyses.},

keywords = {Case study, Dilatancy, High stress, Mine shaft, Numerical modelling},

pubstate = {published},

tppubtype = {article}

}

@article{Walton2015210,

title = {Non-invasive detection of fractures, fractures zones, and rock damage in a hard rock excavation - experience from the Äspö Hard Rock Laboratory in Sweden},

author = {G Walton and MJ Lato and H Anschütz and MA Perras and MS Diederichs},

url = {https://www.sciencedirect.com/science/article/pii/S001379521530017X},

doi = {https://doi.org/10.1016/j.enggeo.2015.07.010},

isbn = {0013-7952},

year  = {2015},

date = {2015-04-01},

journal = {Engineering Geology},

volume = {196},

number = {210-221},

pages = {210-221},

abstract = {A key requirement for licensing of the construction of underground repositories for nuclear waste is the demonstrated capability to verify design assumptions involving the presence and extent of the excavation damage zone around tunnels, shafts, emplacement holes and caverns. As part of ongoing work to select and refine key technologies and techniques towards this end, geophysical surveys were performed at two locations within the Äspö Hard Rock Laboratory in Sweden. Earth resistivity (RES), induced polarization (IP), and Ground Penetrating Radar (GPR) data were collected using a variety of survey parameters; Light Detection and Ranging (LiDAR) data were collected as a reference for surface structures, surface topography, and site geology. Based on an analysis of the data, models for the Highly Damaged Zone (HDZ) and Excavation Damage Zone (EDZ) at both sites were developed. The HDZ was found to be approximately 5 to 10cm in thickness, and the EDZ was found to extend between 15 and 35cm below the excavation surface. Two-dimensional (2D) RES profiling generated the most reliable assessment of the HDZ, whereas chargeability data and GPR data were more useful in the estimation of the EDZ dimensions.},

keywords = {excavation damage zone (EDZ), Geophysical mapping, Ground Penetrating Radar (GPR), LiDAR, Resistivity survey},

pubstate = {published},

tppubtype = {article}

}

@article{Langford201591,

title = {Quantifying uncertainty in Hoek-Brown intact strength envelopes},

author = {JC Langford and MS Diederichs},

url = {https://www.sciencedirect.com/science/article/pii/S1365160915000040},

doi = {https://doi.org/10.1016/j.ijrmms.2014.12.008},

isbn = {1365-1609},

year  = {2015},

date = {2015-02-01},

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

volume = {74},

pages = {91-102},

abstract = {Uncertainty plays a critical role in geotechnical design projects. In addition to the natural variability of geomaterials, testing, transformation and modelling errors must also be considered to accurately characterize rockmass behaviour. By using statistical methods to quantify the intact rock strength and a measure of rockmass quality, a greater understanding of the variability in ground response and support performance can be achieved. This paper examines the issue of quantifying uncertainty in rockmass strength by using the generalized Hoek–Brown approach, which defines rockmass strength according to the intact strength envelope (based on test data) and the geological strength index (GSI). While uncertainty in GSI can be quantified through either a qualitative or quantitative approach, it is more difficult to assess the uncertainty in the intact strength envelope as it is defined by two correlated variables: the uniaxial compressive strength (UCS) and the Hoek–Brown material constant. A new set of linear and nonlinear regression approaches is proposed that can be used to accurately determine the mean intact strength envelope and quantify uncertainty from test data. A reliability-based design method is then presented that quantifies and utilizes uncertainty information at each stage of design to obtain a more complete understanding of rockmass behaviour. To demonstrate the usefulness of this approach, a reliability assessment is performed for a circular excavation under hydrostatic loading conditions.},

keywords = {Composite Geological Strength Index, Generalized Hoek-Brown criterion, Reliability-based design, Rockmass characterization, Uncertainty},

pubstate = {published},

tppubtype = {article}

}

@article{Walton2015,

title = {A new model for the dilation of brittle rocks based on laboratory compression test data with separate treatment of dilatancy mobilization and decay},

author = {G Walton and MS Diederichs},

doi = {https://doi.org/10.1007/s10706-015-9849-9},

year  = {2015},

date = {2015-01-30},

journal = {Geotechnical and Geological Engineering},

volume = {33},

pages = {661-679},

abstract = {In this study, a new model is presented for the dilation angle of rocks which deform through brittle mechanisms in laboratory compression tests. This model, which is defined by a smaller number of independent parameters than similar models, is shown to fit laboratory test data for a wide variety of rocks (sedimentary rocks, diabase, marble, granites, and quartzite). A detailed investigation of each model parameter is performed, and potential links to geological and geotechnical properties are made. A mechanistic interpretation of the observed dilation angle data is also presented, in the context of the new model. Model parameters for the rock types studied are presented, and recommendations for parameter determination/estimation are made. The key strength of the model is shown to be its flexibility to accommodate a data-poor or data-rich analysis, as well as a simplified or comprehensive implementation. Practical guidance for model modifications is provided.},

keywords = {brittle rock, Dilation angle, Engineering rock mechanics, Laboratory testing, Post-yield},

pubstate = {published},

tppubtype = {article}

}

@article{Day201526,

title = {Common Core: Core logging procedures for characterization of complex rockmasses as input into geomechanical analysis for tunnel design},

author = {JJ Day and MS Diederichs},

year  = {2015},

date = {2015-01-01},

journal = {Tunnels and Tunnelling},

volume = {1},

pages = {26-32},

keywords = {Complex rockmasses, Drill core sample selection, geomechanics, tunnel design},

pubstate = {published},

tppubtype = {article}

}

@article{Ghazvinian2014,

title = {3D random Voronoi grain-based models for simulation of brittle rock damage and fabric-guided micro-fracturing},

author = {E Ghazvinian and MS Diederichs and R Quey},

doi = {10.1016/j.jrmge.2014.09.001},

year  = {2014},

date = {2014-12-01},

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

volume = {6},

number = {6},

pages = {506-521},

abstract = {A grain-based distinct element model featuring three-dimensional (3D) Voronoi tessellations (random poly-crystals) is proposed for simulation of crack damage development in brittle rocks. The grain boundaries in poly-crystal structure produced by Voronoi tessellations can represent flaws in intact rock and allow for numerical replication of crack damage progression through initiation and propagation of micro-fractures along grain boundaries. The Voronoi modelling scheme has been used widely in the past for brittle fracture simulation of rock materials. However the difficulty of generating 3D Voronoi models has limited its application to two-dimensional (2D) codes. The proposed approach is implemented in Neper, an open-source engine for generation of 3D Voronoi grains, to generate block geometry files that can be read directly into 3DEC. A series of Unconfined Compressive Strength (UCS) tests are simulated in 3DEC to verify the proposed methodology for 3D simulation of brittle fractures and to investigate the relationship between each micro-parameter and the model's macro-response. The possibility of numerical replication of the classical U-shape strength curve for anisotropic rocks is also investigated in numerical UCS tests by using complex-shaped (elongated) grains that are cemented to one another along their adjoining sides. A micro-parameter calibration procedure is established for 3D Voronoi models for accurate replication of the mechanical behaviour of isotropic and anisotropic (containing a fabric) rocks.},

keywords = {3D Voronoi tessellation, Anisotropy, Crack damage thresholds, Discrete element method, Fabric-guided micro-fracturing, Grain-based model, Numerical modelling},

pubstate = {published},

tppubtype = {article}

}

@article{Oke2014546,

title = {Numerical Analyses in the Design of Umbrella Arch Systems.},

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

url = {https://www.sciencedirect.com/science/article/pii/S1674775514000894},

doi = {https://doi.org/10.1016/j.jrmge.2014.09.005},

issn = {1674-7755},

year  = {2014},

date = {2014-12-01},

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

volume = {6},

number = {6},

pages = {546-564},

abstract = {Due to advances in numerical modelling, it is possible to capture complex support-ground interaction in two dimensions and three dimensions for mechanical analysis of complex tunnel support systems, although such analysis may still be too complex for routine design calculations. One such system is the forepole element, installed within the umbrella arch temporary support system for tunnels, which warrants such support measures. A review of engineering literature illustrates that a lack of design standards exists regarding the use of forepole elements. Therefore, when designing such support, designers must employ complex numerical models combined with engineering judgement. With reference to past developments by others and new investigations conducted by the authors on the Driskos tunnel in Greece and the Istanbul metro, this paper illustrates how advanced numerical modelling tools can facilitate understanding of the influences of design parameters associated with the use of forepole elements. In addition, this paper highlights the complexity of the ground-support interaction when simulated with two-dimensional (2D) finite element software using a homogenous reinforced region, and three-dimensional (3D) finite difference software using structural elements. This paper further illustrates sequential optimisation of two design parameters (spacing and overlap) using numerical modelling. With regard to capturing system behaviour in the region between forepoles for the purpose of dimensioning spacing, this paper employs three distinctive advanced numerical models: particle codes, continuous finite element models with joint set and Voronoi blocks. Finally, to capture the behaviour/failure ahead of the tunnel face (overlap parameter), 2D axisymmetric models are employed. Finally, conclusions of 2D and 3D numerical assessment on the Driskos tunnel are drawn. The data enriched case study is examined to determine an optimum design, based on the proposed optimisation of design parameters, of forepole elements related to the site-specific considerations.},

keywords = {Forepole, Numerical analysis, Numerical modelling, tunnel design, Umbrella arch},

pubstate = {published},

tppubtype = {article}

}

@article{Walton2014522,

title = {Verification of a lab-based dilation model for in-situ conditions using continuum models},

author = {G Walton and MS Diederichs and LR Alejano and J Arzúa},

url = {https://www.sciencedirect.com/science/article/pii/S1674775514000869},

doi = {https://doi.org/10.1016/j.jrmge.2014.09.004},

issn = {1674-7755},

year  = {2014},

date = {2014-12-01},

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

volume = {6},

number = {6},

pages = {552-534},

abstract = {With respect to constitutive models for continuum modeling applications, the post-yield domain remains the area of greatest uncertainty. Recent studies based on laboratory testing have led to the development of a number of models for brittle rock dilation, which account for both the plastic shear strain and confining stress dependencies of this phenomenon. Although these models are useful in providing an improved understanding of how dilatancy evolves during a compression test, there has been relatively little work performed examining their validity for modeling brittle rock yield in situ. In this study, different constitutive models for rock dilation are reviewed and then tested, in the context of a number of case studies, using a continuum finite-difference approach (FLAC). The uncertainty associated with the modeling of brittle fracture localization is addressed, and the overall ability of mobilized dilation models to replicate in situ deformation measurements and yield patterns is evaluated.},

keywords = {brittle rock, Case study, continuum modelling, Dilation},

pubstate = {published},

tppubtype = {article}

}