Rock Mechanics.pdf - Mining and Blasting

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Figure 14.9 A method of pillar recovery in open stoping, using a cohesive backfill to control stope-wall behaviour. BACKFILL APPLICATIONS IN OPEN AND BENCH STOPING The ability of cemented backfill to undergo autogenous healing, during placement of superincumbent layers of the fill mass, is also determined by the composition of the cementitious materials, and the physical conditions existing during curing. Pillar recovery adjacent to backfill usually involves detonation of explosive charges in rock close to the fill–rock interface, and questions arise about the effect of the associated dynamic loading on the integrity of the fill mass. Using the terminology adopted in Chapter 10, the difference in the characteristic impedances of rock and backfill is such that very little dynamic strain energy can be transmitted into the fill medium. Nevertheless, even a low magnitude stress wave in a fill mass may be sufficient to cause sufficient pore pressure increase to pose a risk of liquefaction, particularly where the fill is saturated and close to the critical state, in soil mechanics terms. In the case where a blast hole is located close to the interface, i.e. within about 10–15 blasthole diameters, the risk arises of detonation product gases acting directly on the fill surface. There is then an obvious risk of superficial damage to the fill structure. A key issue in the effective use of backfill for artificial support during pillar mining is complete integration of the initial, primary stoping phase with the subsequent phase, mining of pillar ore as secondary stopes. This requires that the general mining strategy 425
Figure 14.10 Sublevel open stoping and filling in the Valisaari orebody, Vihanti Mine (after Koskela, 1983). ARTIFICIALLY SUPPORTED MINING METHODS be established early in the life of the orebody. It then allows explicit decisions to be made on the proportion of ore to be extracted in the primary stoping phase. This is a question that has to be considered carefully, since, although primary open stoping usually proceeds under conditions of easy mining with little dilution, primary stope voids require stabilised backfill for later mining of pillars. Excessive primary stoping can thereby encumber pillar mining with costs (related to the cement addition to the primary stope backfill) which would render large-scale pillar extraction unprofitable. Some interesting case studies illustrate the improved ground control and increased recovery of the mineral reserve derived from the use of stabilised backfill and exploiting the principles discussed above. Koskela (1983) describes several open stope and filling operations in Finnish mines. In the Valisaari orebody of the Vihanti Mine, the typical extraction sequence may be inferred from Figure 14.10. A central stope is mined and filled with a backfill obtained from de-slimed concentrator tailings, and stabilised with a pozzolan of finely ground, granulated blast furnace slag activated with slaked lime. The fill mix consists of lime/slag in the proportion 1.5/100, added to sandfill in the slag/sandfill proportion of 1/11. The pulp density of the mix is controlled at 40% water per unit weight of mixture. When the backfill mix is introduced into the centre of the stope from hangingwall fill points, fine material containing a high proportion of slag reports to the stope walls. The centre of the fill mass is therefore weaker than backfill abutting the stope boundaries. Filling practice involves the construction of fill dams or bulkheads in the original stope accesses and installation of filter and drainage lines. Bulkheads are designed to withstand 0.5 MPa earth pressure on the lower sublevels, and 0.25 MPa in the upper sublevels. Coarse backfill is introduced at the bottom of the stope to provide base drainage, and filter lines are erected from the stope base to each sublevel. The filter lines are made from agricultural drainage pipe. Backfill prepared and placed in this way has a dry unit weight (d) of about 16.5 kN m −3 . One year after emplacement, the in situ strength of the mass is 1.05 MPa. The peak strength is achieved in 3 to 5 years. At that time, during adjacent stoping the fill mass may support vertical fill face exposures 100 m high and 60 m wide. Application of paste fill is illustrated by bench-and-fill stoping at the Neves Corvo Mine, Portugal (Hepworth and Caupers, 2001, Been et al., 2002). The mining method is shown in Figure 14.11, where primary bench stopes are mined transversely across 426
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Rock Mechanics
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Rock Mechanics for underground mini
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Contents Preface to the third editi
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CONTENTS 9 Excavation design in blo
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CONTENTS ix Appendix A Basic constr
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PREFACE TO THE THIRD EDITION Mining
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PREFACE TO THE SECOND EDITION In th
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PREFACE TO THE FIRST EDITION design
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ACKNOWLEDGEMENTS Safety in Mines Re
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Figure 1.1 (a) Pre-mining condition
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ROCK MECHANICS AND MINING ENGINEERI
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Figure 1.4 Principal features of a
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10 Figure 1.5 Definition of activit
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Figure 1.7 Components and logic of
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Figure 2.1 (a) A finite body subjec
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Figure 2.2 Free-body diagram for es
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STRESS AND INFINITESIMAL STRAIN As
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STRESS AND INFINITESIMAL STRAIN In
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Figure 2.3 Free-body diagram for de
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Figure 2.5 Problem geometry for det
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Figure 2.7 Rigid-body rotation of a
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STRESS AND INFINITESIMAL STRAIN the
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STRESS AND INFINITESIMAL STRAIN str
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⎡ ⎢ ⎣ xx yy zz xy yz zx STRES
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Figure 2.11 Cylindrical polar coord
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STRESS AND INFINITESIMAL STRAIN fre
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Figure 2.13 Construction of a Mohr
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STRESS AND INFINITESIMAL STRAIN fun
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3 Rock Figure 3.1 Sidewall failure
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Figure 3.2 Jointing in a folded str
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Figure 3.5 Diagrammatic longitudina
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Figure 3.7 Discontinuity spacing hi
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Figure 3.9 Illustration of persiste
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Figure 3.11 Typical roughness profi
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ROCK MASS STRUCTURE AND CHARACTERIS
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Figure 3.17 Sample number vs. preci
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Figure 3.19 Diagrammatic illustrati
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Figure 3.20 Computerised depiction
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Figure 3.23 Stereographic projectio
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Figure 3.26 Polar stereographic net
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Figure 3.28 Contours of pole concen
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Figure 3.30 Geological Strength Ind
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Figure 4.1 Idealised illustration o
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ROCK STRENGTH AND DEFORMABILITY wit
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Figure 4.4 Influence of end restrai
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ROCK STRENGTH AND DEFORMABILITY whe
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Figure 4.8 Principle of closed-loop
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Figure 4.12 Two classes of stress-
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Figure 4.14 Point load test apparat
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Figure 4.15 Biaxial compression tes
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Figure 4.18 Results of triaxial com
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ROCK STRENGTH AND DEFORMABILITY was
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Figure 4.23 Coulomb strength envelo
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Figure 4.25 Extension of a preexist
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Figure 4.29 The three basic modes o
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Figure 4.30 Normalised peak strengt
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ROCK STRENGTH AND DEFORMABILITY Tab
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Figure 4.32 The normality condition
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Figure 4.33 Variation of peak princ
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Figure 4.35 Direct shear test confi
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Figure 4.37 Shear stress-shear disp
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Figure 4.40 Peak and residual effec
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Figure 4.43 Effect of shearing dire
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Figure 4.45 Relations between norma
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Figure 4.47 Coulomb friction, linea
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ROCK STRENGTH AND DEFORMABILITY whe
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Figure 4.49 Composite peak strength
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Figure 4.50 Hoek-Brown peak strengt
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Figure 4.52 Determination of the Yo
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ROCK STRENGTH AND DEFORMABILITY 4 A
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5 Pre-mining Figure 5.1 Method of s
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Figure 5.2 The effect of irregular
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PRE-MINING STATE OF STRESS surround
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PRE-MINING STATE OF STRESS induced
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Figure 5.5 (a) Definition of hole l
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Figure 5.6 (a) Core drilling a slot
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Figure 5.7 Principles of stress mea
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PRE-MINING STATE OF STRESS strength
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PRE-MINING STATE OF STRESS A second
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PRE-MINING STATE OF STRESS by the e
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PRE-MINING STATE OF STRESS extend i
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PRE-MINING STATE OF STRESS (d) Dete
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METHODS OF STRESS ANALYSIS quantita
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METHODS OF STRESS ANALYSIS It is in
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Figure 6.2 A thick-walled cylinder
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METHODS OF STRESS ANALYSIS For the
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Figure 6.3 Problem geometry, coordi
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Figure 6.4 Problem geometry, coordi
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METHODS OF STRESS ANALYSIS When the
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Figure 6.5 Superposition scheme dem
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METHODS OF STRESS ANALYSIS The disc
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Figure 6.7 Development of a finite
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METHODS OF STRESS ANALYSIS Solution
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Figure 6.8 A simple finite element
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Figure 6.9 A schematic representati
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METHODS OF STRESS ANALYSIS block ce
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METHODS OF STRESS ANALYSIS where ˚
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METHODS OF STRESS ANALYSIS The prin
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EXCAVATION DESIGN IN MASSIVE ELASTI
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Figure 7.2 A logical framework for
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Figure 7.3 (a) Axisymmetric stress
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Figure 7.6 A plane of weakness, ori
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Figure 7.8 A flat-lying plane of we
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Figure 7.10 Shear stress/normal str
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Figure 7.12 Ovaloidal opening in a
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Figure 7.15 States of stress at sel
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Figure 7.16 Prediction of the exten
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Figure 7.18 Contour plots of princi
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Figure 7.19 Problem geometry for de
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8 Excavation Figure 8.1 An excavati
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EXCAVATION DESIGN IN STRATIFIED ROC
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Figure 8.4 Experimental apparatus f
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Figure 8.7 Free body diagrams and n
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Figure 8.8 Assumed distributions of
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Figure 8.9 Flow chart for the deter
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Figure 8.10 Normalised arch thickne
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EXCAVATION DESIGN IN STRATIFIED ROC
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Figure 8.11 Normalised deflection a
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9 Excavation Figure 9.1 Generation
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Figure 9.3 (a) A finite, non-tapere
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(a) (b) Figure 9.4 (a) Vertical cro
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(a) (b) (c) EP EP Reference circle
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Figure 9.10 JP 100 is the only JP w
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Figure 9.12 Traces of the views of
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EXCAVATION DESIGN IN BLOCKY ROCK In
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Figure 9.14 Free-body diagrams of a
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EXCAVATION DESIGN IN BLOCKY ROCK di
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Figure 9.16 Symmetrical wedge in th
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Figure 9.17 (a) Geometry for determ
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Figure 9.18 Problem geometry demons
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Figure 9.20 Cut-and-fill stope mine
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Figure 9.22 Chart to determine fact
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EXCAVATION DESIGN IN BLOCKY ROCK Th
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Figure 10.1 (a) Pre-mining state of
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Figure 10.3 (a) Dynamic loading of
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Figure 10.5 (a) Pre-mining and (b)
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Figure 10.6 Problem definition and
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ENERGY, MINE STABILITY, MINE SEISMI
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Figure 10.9 Force and stress compon
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Figure 10.12 Distribution of radial
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Figure 10.15 Problem geometry for d
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Figure 10.17 (a) Schematic represen
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Figure 10.20 Elastic/post-peak stif
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Figure 10.24 Relation between frequ
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Figure 10.28 Six possible ways that
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Figure 10.29 First motions for P an
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11Rock support and reinforcement 11
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Figure 11.1 (a) Hypothetical exampl
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Figure 11.4 Non-linear support reac
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Figure 11.5 Idealised elastic-britt
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Figure 11.6 Calculated required sup
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ROCK SUPPORT AND REINFORCEMENT The
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Figure 11.9 Ground reaction curves
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Figure 11.12 Use of grouted reinfor
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ROCK SUPPORT AND REINFORCEMENT If,
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Figure 11.16 Local reinforcement ac
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Figure 11.18 Typical working sketch
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Figure 11.19 Permanent support and
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Figure 11.22 Basis of natural coord
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Figure 11.24 Distributions of (a) s
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Figure 11.26 Resin grouted rockbolt
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Figure 11.28 Alternative methods of
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ROCK SUPPORT AND REINFORCEMENT Tabl
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Figure 11.31 Toussaint-Heintzmann y
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MINING METHODS AND METHOD SELECTION
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Figure 12.2 Elements of a supported
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Figure 12.6 Schematic layout for bi
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Figure 12.8 Layout for shrink stopi
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Figure 12.9 Schematic layout for VC
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Figure 12.11 Key elements of longwa
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Figure 12.13 Mining layout for tran
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13 Figure 13.1 Schematic illustrati
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Figure 13.3 Layout of barrier pilla
Page 391 and 392: Figure 13.5 Principal modes of defo
Page 393 and 394: Figure 13.8 Geometry for tributary
Page 395 and 396: PILLAR SUPPORTED MINING METHODS str
Page 397 and 398: Figure 13.10 Distribution of vertic
Page 399 and 400: Figure 13.12 Pillar behaviour domai
Page 401 and 402: PILLAR SUPPORTED MINING METHODS Lun
Page 403 and 404: Figure 13.15 Options in the design
Page 405 and 406: Figure 13.17 Relation between yield
Page 407 and 408: Figure 13.19 Model of yield of coun
Page 409 and 410: Figure 13.20 North-south vertical c
Page 411 and 412: Figure 13.23 Stope-and-pillar layou
Page 413 and 414: Figure 13.25 Calibrated stability c
Page 415 and 416: PILLAR SUPPORTED MINING METHODS wor
Page 417 and 418: Figure 13.28 Pillar performance, de
Page 419 and 420: Figure 13.29 (a) Stope and pillar l
Page 421 and 422: Figure 13.31 (a) Plane strain analy
Page 423 and 424: PILLAR SUPPORTED MINING METHODS Pan
Page 425 and 426: 14 Artificially supported mining me
Page 427 and 428: ARTIFICIALLY SUPPORTED MINING METHO
Page 431 and 432: Figure 14.2 Simplified view of stru
Page 435 and 436: Figure 14.5 Confined block model fo
Page 437 and 438: Figure 14.7 Crown and sidewall stre
Page 441: ARTIFICIALLY SUPPORTED MINING METHO
Page 445 and 446: Figure 14.12 Some applications of c
Page 447 and 448: 15 Longwall and caving mining metho
Page 449 and 450: Figure 15.2 Shear stress drop in th
Page 451 and 452: LONGWALL AND CAVING MINING METHODS
Page 455 and 456: Figure 15.6 Hydraulic prop reaction
Page 457 and 458: Figure 15.7 Development and extract
Page 459 and 460: Figure 15.8 Vertical stress redistr
Page 461 and 462: Figure 15.11 Distribution of observ
Page 463 and 464: Figure 15.13 Plan view of microseis
Page 465 and 466: Figure 15.16 Ground-support interac
Page 467 and 468: Figure 15.18 Roadway support and re
Page 475 and 476: Figure 15.25 Comparison of isolated
Page 477 and 478: Figure 15.26 Geometry of a sublevel
Page 479 and 480: Figure 15.28 Theoretical determinat
Page 481 and 482: Figure 15.31 Deterioration of a cro
Page 483 and 484: Figure 15.32 Distinct element simul
Page 487 and 488: Figure 15.34 Extended Mathews stabi
Page 489 and 490: Figure 15.36 Comparison of postand
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Figure 15.39 Idealised plan illustr
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Figure 15.41 Idealised vertical sec
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Figure 15.42 Vertical slice through
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LONGWALL AND CAVING MINING METHODS
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16 Figure 16.1 Trough subsidence ov
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MINING-INDUCED SURFACE SUBSIDENCE c
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Figure 16.4 North-south section, At
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Figure 16.6 (a) Rectangular block g
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MINING-INDUCED SURFACE SUBSIDENCE f
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Figure 16.8 Relation between stope
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MINING-INDUCED SURFACE SUBSIDENCE M
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MINING-INDUCED SURFACE SUBSIDENCE
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Figure 16.14 Chart developed to est
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Figure 16.16 Progressive hangingwal
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Figure 16.19 Idealised model used i
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Figure 16.21 Longitudinal section,
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MINING-INDUCED SURFACE SUBSIDENCE t
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MINING-INDUCED SURFACE SUBSIDENCE w
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MINING-INDUCED SURFACE SUBSIDENCE F
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Figure 16.25 Subsidence troughs pre
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Figure 16.28 Predicted and measured
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17 Blasting mechanics 17.1 Blasting
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Figure 17.1 An empirical matching o
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Figure 17.2 A finite difference mod
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Figure 17.4 Reflection of a cylindr
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BLASTING MECHANICS means that no ci
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Figure 17.8 Layout of blast holes i
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Figure 17.9 Influence of field stat
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Figure 17.11 Generation of surface
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BLASTING MECHANICS The components o
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BLASTING MECHANICS amplitudes of th
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BLASTING MECHANICS 17.9 Evaluation
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Figure 17.15 (a) Schematic cross se
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BLASTING MECHANICS in Figure 17.17,
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MONITORING ROCK MASS PERFORMANCE (a
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MONITORING ROCK MASS PERFORMANCE su
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MONITORING ROCK MASS PERFORMANCE Ta
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Figure 18.2 The Distometer ISETH, a
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Figure 18.5 Self-inductance multipl
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MONITORING ROCK MASS PERFORMANCE is
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Figure 18.9 Biaxial vibrating wire
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MONITORING ROCK MASS PERFORMANCE me
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Figure 18.12 Cross section at 6650N
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Figure 18.13 Examples of convergenc
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Figure 18.15 Longitudinal section l
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Figure 18.16 (Cont.) MONITORING ROC
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Appendix A Basic constructions usin
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Figure A.3 Determining the angle be
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APPENDIX A USE OF HEMISPHERICAL PRO
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APPENDIX B STRESSES AND DISPLACEMEN
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Figure A.6 Axisymmetric tunnel prob
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Figure A.9 Bolt load-extension curv
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APPENDIX D LIMITING EQUILIBRIUM ANA
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ANSWERS TO PROBLEMS 2 (a) 0.087 - 0
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ANSWERS TO PROBLEMS 3 wp = 38.6 m,
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REFERENCES Symp. & 17th Tunn. Assn
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REFERENCES Brady, B. H. G. and Bray
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REFERENCES Collier, P. A. (1993) De
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REFERENCES Drescher, A. and Vardoul
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REFERENCES Gustafsson, P. (1998) Wa
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REFERENCES Hood, M. and Brown, E. T
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REFERENCES Kaiser, P. K. and Tannan
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REFERENCES Lorig, L. J. and Brady,
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REFERENCES Ortlepp, W. D. (1994) Gr
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REFERENCES Rojas, E., Molina, R. an
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REFERENCES Spottiswoode, S. M. and
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REFERENCES Villaescusa, E., Windsor
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Index Page numbers appearing in bol
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INDEX Coulomb (cont.) parameters 96
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INDEX Excavation (cont.) support ra
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INDEX Jaeger’s plane of weakness
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INDEX Panel caving 470-2, 473, 474,
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INDEX Seismic (cont.) moment 306, 3
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INDEX Strength (cont.) residual 86,
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INDEX United States (USA) 395, 396,
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