Rock Mechanics.pdf - Mining and Blasting

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LONGWALL MINING IN HARD ROCK followed by a zone of influence and a stability analysis, considering hangingwall failure due to buckling, shear and block rotation. This gives a maximum safe spacing of the individual support elements. The calculations are carried out for both static (rock fall) and dynamic (rockburst) conditions. Daehnke et al. (2001) illustrate their methodology with a worked example. Detailed design methods are also presented by Ryder and Jager (2002). Tunnel support and reinforcement. As well as carrying out the functions of support and reinforcement systems discussed in Chapter 11, the support and reinforcement systems used in the off-reef tunnels associated with hard rock longwall mining and its variants, may also have to be dynamically capable to alleviate the rockburst hazard. The support and reinforcement systems must be capable of reinforcing and retaining or holding the rock mass in place, and surface support or containment of the broken rock at the excavation boundary under both static and dynamic loading conditions. It must be noted that rockburst conditions may also exist in mines that are less deep and use different mining methods than the deep level gold mines of South Africa (e.g. Li et al., 2003, Rojas et al., 2000, Simser et al., 2002). Under these conditions, the reinforcing elements may consist of rock bolts, cable bolts, studs and tendons, often with yielding capability. The surface support elements may include shotcrete or other sprayed liners, mesh, straps, wire rope lacing, fixtures of a range of types, and energy absorbing face plates. An example of the system used in the haulage level of a South African gold mine is shown in Figure 11.30. As in the case of stope support, the design methodology used for dynamically capable tunnel support and reinforcement has been based on tributary area and energy absorption concepts (e.g. Wagner, 1984, Ortlepp, 1994). Recognising that it is not practicable to attempt to prevent fracturing and displacement in the event of a rockburst, tunnel support and reinforcement systems are designed to yield and absorb energy, limit the amount of deformation occurring at the tunnel boundary, and contain the fractured rock mass at the excavation periphery (Roberts and Brummer, 1988). It is postulated that, in a rockburst, blocks or slabs of rock will be accelerated and ejected from the tunnel boundary. In its simplest form, the energy released by the rock mass and required to be absorbed by the support and reinforcement system, E, is given by E = 1 2 mv2 + mgh where m is the mass of rock ejected from the excavation, v is the ejection velocity and h is the height through which the rock falls in coming to rest. The ejection velocity may be up to 10 m s −1 in extreme cases but is often taken to be more like3ms −1 for design. The use of this approach has directed emphasis towards the development of a range of reinforcing elements that are able to yield or displace while retaining significant load carrying capability. In the standard design methodology, this approach is usually applied with a tributary area assigned to each reinforcing element (Ortlepp, 1994). However, on the basis of results obtained in a large-scale field experiment, Haile and Le Bron (2001) questioned the validity of the tributary area approach under the complex dynamic loading conditions resulting from mininginduced seismicity. Li et al. (2003) suggested that momentum change should be used as an additional design criterion. They also demonstrated the practical value of cable bolt plates made from conveyor belt material in absorbing incident energy 439
Figure 15.7 Development and extraction of adjacent longwalls using multiple roadways illustrating the chain pillar loading cycle (after Colwell et al., 1999). LONGWALL AND CAVING MINING METHODS and improving the load carrying capabilities of tunnel support and reinforcement systems. 15.3 Longwall coal mining 15.3.1 Basic geomechanics considerations The elements of the longwall method of coal mining are illustrated in Figure 12.12. As with longwall mining in hard rock, the primary objective of mining design is to achieve pseudo-continuous deformation of the main upper strata overlying the seam. The differences between the layouts and the mining and strata control techniques used in the two cases arise essentially from the appreciably lower strengths of coal measures rocks. In the United Kingdom, for example, the uniaxial compressive strengths of the roof, seam and floor rocks are typically in the range 20–40 MPa. The pre-mining stress field is difficult to measure in these weak, sedimentary rocks, but back analyses based on observed excavation performance suggest that, in the UK coal fields, the stress field is approximately hydrostatic with magnitude p = h, where is the weighted average unit weight of the superincumbent strata and h is the mining depth. Longwall mining is a highly productive method which aims to extract almost 100% of selected blocks of the resource. In most applications of the method, a number of parallel panels or longwalls are extracted side-by-side as illustrated in Figure 15.7. The most common longwall method of mining coal is now a retreat method in which the roadways are developed to the end of the panel which is then extracted on retreat as illustrated in Figure 15.7. The pillars left between adjacent longwalls serve to protect the roadways from the excessive displacements that may be associated with the mining of adjacent panels, to isolate a particular panel where unfavourable geological structures or fire, water, or gas hazards exists, or to assist in controlling surface subsidence. The important issue of the surface subsidence associated with longwall 440
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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
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Figure 13.5 Principal modes of defo
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Figure 13.8 Geometry for tributary
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PILLAR SUPPORTED MINING METHODS str
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Figure 13.10 Distribution of vertic
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Figure 13.12 Pillar behaviour domai
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PILLAR SUPPORTED MINING METHODS Lun
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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 443 and 444: Figure 14.10 Sublevel open stoping
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: Figure 15.6 Hydraulic prop reaction
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
Page 493 and 494: Figure 15.39 Idealised plan illustr
Page 495 and 496: Figure 15.41 Idealised vertical sec
Page 497 and 498: Figure 15.42 Vertical slice through
Page 501 and 502: 16 Figure 16.1 Trough subsidence ov
Page 503 and 504: MINING-INDUCED SURFACE SUBSIDENCE c
Page 505 and 506: 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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