title of the thesis - Department of Geology - Queen's University

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$Fayek & Kyser 2000 uraninite fractionations.pdf - Queen's University$

Chapter 4 Modelling Stress in the Creighton Deep 4.1 Introduction Stress in the mine environment results from a superposition of regional tectonic stresses, local stress induced by mining geometry and material extraction and is also influenced by the presence of geological structures and differences in material properties. It is impossible to model exact stress conditions within a mine because of the complex nature of rock and the unknown state of the pre-mining stress conditions. However, simplified constitutive models with specified material properties, initial and boundary conditions allow for insight into more complex rock mass and fault behaviour. Numerical stress analysis models of the 7400 Level at Creighton Mine were used to provide insight into: the influences of mining geometry and structure on stress distribution in the mine; the extent of the yield zone surrounding the excavation; and the amount of induced displacement along faults. The sensitivity of modelled results was assessed by varying the fault strength, selectively weakening faults based on geological insight and by changing boundary stress conditions. In doing so, constraints were placed on existing stress conditions. The ultimate goal of the numerical modelling is to compare modelled stress with observed seismicity and integrate geological knowledge of the rock mass, in order to develop an understanding of the influence of the structural system in the Creighton Deep on seismic behaviour. 78
4.2 Numerical Methods Phase 2 and Universal Distinct Element Code (UDEC) are two numerical stress analysis packages that were used to model and simulate stress on the 7400 Level. Phase 2 , developed by Rocscience (Rocscience Inc., 2005), is a continuum code that employs the finite element method. Using this program the model is discretized into a mesh of triangular elements and nodes (Fig. 4.1). When boundary conditions are applied, displacements are computed at each node. The displacements within elements are used to calculate strains for each element. Strain is then translated into stress, integrating rockmass properties (Pande et al., 1990). The behaviour of both the continuum and discontinuities in this thesis is assumed to be governed by Mohr-Coulomb failure criteria. UDEC, developed by Itasca Consulting Group, Inc. (2000), is a discontinuum code that employs the distinct element method. A discontinuum model differs from the continuum model in that the Figure 4.1: Schematic diagram of triangular elements and nodes. model is defined by contacts and interfaces that separate rigid and/or deformable blocks (Cundall and Hart, 1992; Hart, 2003). UDEC models use a continuum mesh inside blocks. Contacts are allowed to interact and deform (Jing, 2003). Unlike the finite element method, the UDEC model allows for evolving contact conditions. The model proceeds through a series of time steps – a feed-forward process where results from the previous iterations are used for the next. UDEC works by applying the force-displacement law at contacts and formulating and solving equations of motion (Newton’s second law) for the defined blocks (Hart, 2003). Using block properties, forces and displacements are translated into stress and strain for each bock. As strain is accumulated, these quantities are recalculated and used as inputs for the next time step. As the model progresses, it recognizes block rotation, sliding contacts, block detachment and new interfaces between blocks 79
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THE INFLUENCES OF STRESS AND STRUCT
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esulting in increased stress to the
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Table of Contents Abstract.........
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4.6.1 Fracture Reactivation........
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List of Figures Figure 1.1: Locatio
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Figure 3.23: Preliminary stress inv
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Figure B11: Events between Jan 1, 2
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List of Tables Table 2.1: Geologica
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Chapter 1 Introduction 1.1 Backgrou
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Figure 1.1: Location of Sudbury and
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Chapter 2 Geological Assessment of
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ack breccia and sediments later dep
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Murray Fault, the principal fault o
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2.2 Local Geology of Creighton Mine
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B West East B’ Figure 2.4B: Longi
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Table 2.2: Fault systems within the
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Table 2.3: Summary of Fault Charact
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Figure 2.6: (A) Damage to shotcrete
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Figure 2.7: (A) The 1290 Shear Zone
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Figure 2.8: Images of (A) the 400-E
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Figure 2.9: (A) Photograph of the c
Page 43 and 44: Figure 2.10 (A) Shear foliation, in
Page 45 and 46: Figure 2.11: Thin sections of the F
Page 47 and 48: (Fig. 2.12B). Reduction of quartz g
Page 49 and 50: 2.3.11 Late-Stage Fractures The you
Page 51 and 52: overprinting (Cochrane, 1991; Couls
Page 53 and 54: Table 2.4: Summary of Proterozoic t
Page 55 and 56: Both of these inferred stress direc
Page 57 and 58: are, at this time, in the process o
Page 59 and 60: Microseismic events of this subset
Page 61 and 62: 3.2.1.2 Seismic Energy (E o ) and S
Page 63 and 64: 3.2.1.4 Stress Parameters Stress pa
Page 65 and 66: located events were removed from cl
Page 67 and 68: Figure 3.7: Detected seismicity cor
Page 69 and 70: Table 3.1: Event characteristics in
Page 71 and 72: Table 3.3: Summary of relevant para
Page 73 and 74: ) Damage Zone The rock mass in the
Page 75 and 76: quadrants of dilatation and compres
Page 77 and 78: Figure 3.12: Lower hemisphere equal
Page 79 and 80: mechanism shows that over 57% of th
Page 81 and 82: Figure 3.16: Classification of prin
Page 83 and 84: Figure 3.18: Contoured P-axis, B-ax
Page 85 and 86: Figure 3.20: Distribution of double
Page 87 and 88: This parameter reflects the magnitu
Page 89 and 90: Figure 3.23: Preliminary stress inv
Page 91 and 92: Figure 3.25: Equal area stereonet s
Page 93: Figure 3.27: (A) Maximum principal
Page 97 and 98: Stress-strain relationships are use
Page 99 and 100: Rock mass failure is governed by th
Page 101 and 102: Figure 4.5: (A) Model for tectonic
Page 103 and 104: The zero cohesion and low friction
Page 105 and 106: Figure 4.9: Model of yielding for C
Page 107 and 108: Figure 4.11: Model of differential
Page 109 and 110: Figure 4.14: Model of maximum stres
Page 111 and 112: stress field model. There is little
Page 113 and 114: clustering are indications of rock
Page 115 and 116: Figure 4.23: Contoured domains of s
Page 117 and 118: Figure 4.24: Fracture initiation th
Page 119 and 120: seismic Cluster 1, which correspond
Page 121 and 122: contains energetic events and is no
Page 123 and 124: preferentially oriented fracture pl
Page 125 and 126: methodologies employed are of value
Page 127 and 128: References Alcott, J. M., Kaiser, P
Page 129 and 130: Galkin, V., Mungall, J. (2005). Str
Page 131 and 132: Mungall, J. E., & Hanley, J. J. (20
Page 133 and 134: Appendix A Geological Maps and Samp
Page 135 and 136: A.2 Level Plans with Sample Locatio
Page 137 and 138: Figure A3: 7400 Level, modified for
Page 139 and 140: Figure A5: 7680 Level, modified for
Page 141 and 142: Figure A7: 7940 Ramp, modified from
Page 143 and 144: MICROSEISMIC EVENTS Source Radius A
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2006 Event Frequency with Depth 600
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B.2 Spatial Distribution of Seismic
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Cluster 1 Source Radius Asp. Radius
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Seismic Moment 10.0 9.5 9.0 8.5 8.0
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143 Peak Velocity Parameter -2.5 -2
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B.4.2 Temporal Distribution of Clus
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147 Static Stress Drop 5.0 5.5 6.0
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B.4.3 Temporal Distribution of Clus
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151 Static Stress Drop 4.0 4.5 5.0
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Frequency-Magnitude Relation for Cl
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P-axis B-axis T-axis 155 Fault Plan
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P-axis B-axis T-axis Fault Plane 1
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D.1.1: Case 1 Models Figure D1: Cas
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Figure D3: Case 1, elastic models s
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A B C D Figure D5: Case 1, plastic
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A B C D Figure D7: Case 1, plastic
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D.1.2: Case 2 Models A B C D Figure
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D.1.3: Case 3 Models A B C Figure D
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D1.4 Tectonic Loading Models Figure
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D.2 Discussion of Phase 2 Models El
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Staged models were created in which
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Figure D17 (A) Elastic model showin
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Figure D19 (A) Elastic model showin
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• Similar damage zones surroundin
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; ;================================
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change jmat=1 range 0,1564.64 0,156
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crack (845.579,718.676) (787.063,57
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;===plum=== crack (0,355.2371429) (
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crack (866.14,726.44) (838.2,737.61
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crack (838.2,737.616) (815.848,771.
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crack (815.848,771.144) (815.848,78
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;===== define sub block ===========
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E.9 S3:S1 Model for fracture reacti
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yval= abs(z_syy(zi)) xyval= abs(z_s
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and rearranged to , (Equation F4) .
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Such that , (Equation F19) I is the
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