Rock Mechanics.pdf - Mining and Blasting

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Figure 17.6 Overbreak in a surface bench blast, possibly due to an overrelaxation mechanism. Figure 17.7 Local stress field near a stope face, and the imposed preferred direction of fracture propagation. PERIMETER BLASTING 17.5 Computational models of blasting The qualitative description of explosive action in rock does not present a basis for either design of blasts or for control of the effect of blasting in the surrounding medium. The most promising approaches for the long-term resolution of these needs may lie in the further development of various computational models of the blasting process. Some early and well-conceived schemes were described by Dienes and Margolin (1980), Grady and Kipp (1980) and Margolin (1981). Each is based on a finite difference representation of the explosive–rock interaction, within a continuum mechanics framework. The model described by Margolin is based on: (a) a statistical description of Griffith crack distribution in the medium; (b) a criterion for crack growth; (c) a specification of modulus reduction with crack development; (d) a statistical description of the crack distribution as it evolves in time, taking account of crack growth termination by intersection with other cracks. While these models are not now suitable for routine blast design, they have been used in special cases, such as the design of comminution blasts required for in-situ oil-shale retorting. A particular source of interest in these models is that they seek to predict the macroscopic behaviour of a rock mass from the microscopic theory of fracture and the global equations of continuum mechanics. 17.6 Perimeter blasting The discussion in Chapters 7–9 was concerned with the design of excavations in various types of rock masses. The general assumption in the development of the design methods was that the final mechanical state of the excavation peripheral rock was not affected by the method of creating the opening. Since blasting is an intrinsically violent process, the potential exists in practice for significant local degradation of the mechanical properties of the rock. A well-conceived design philosophy not supported subsequently by appropriate excavation procedures is impossible to reconcile with sound engineering practice. 527
Figure 17.8 Layout of blast holes in a pre-split blast, and transient stress conditions around a blast hole for very short and short delay between initiation of adjacent blast holes. BLASTING MECHANICS Perimeter blasting is the process in which closely controlled blasting practices are applied to produce a geometrically precise and relatively undisturbed ultimate surface. The objectives are to restrict the number and extent of new fractures in the rock, to prevent undue disturbance of the jointed mass, and therefore to preserve the inherent strength of the in situ rock. The consequences of effective perimeter blasting are expressed in the operational performance of the opening. In permanent openings, lower support costs are achieved. In temporary openings, reduced maintenance costs are obtained by reduced scaling. In both cases, excavation development rates may be improved by reduced overbreak, leading to reduced effort in scaling the freshly generated surface, and reduced loading and haulage of development mullock. Finally, smooth walls result in reduced frictional resistance to airflow and improved mine ventilation capacity. There are two techniques of perimeter blasting – pre-splitting and smooth blasting. Both methods are industrially important, and each complements the other in scope for practical application. They are based on the use of decoupled charges, in which the objective is to restrict the development of a rose of cracks around a hole. This is sought by isolating the explosive charge from the blasthole surface, using a charge diameter appreciably less than the blasthole diameter, and using spacers to locate the charge axis along the hole axis. Special explosives, based on NG, are formulated and packaged, to ensure stable detonation of the explosive at relatively low charge diameter. 17.6.1 Pre-split blasting With this method, a continuous fracture which will form the final surface of an excavation is generated in the absence of a local free face. As an example, Figure 17.8a represents a cross section of a development heading. Parallel, close-spaced holes, which will define the excavation perimeter, are drilled in the direction of face advance. 528
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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
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Figure 13.17 Relation between yield
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Figure 13.19 Model of yield of coun
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Figure 13.20 North-south vertical c
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Figure 13.23 Stope-and-pillar layou
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Figure 13.25 Calibrated stability c
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PILLAR SUPPORTED MINING METHODS wor
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Figure 13.28 Pillar performance, de
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Figure 13.29 (a) Stope and pillar l
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Figure 13.31 (a) Plane strain analy
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PILLAR SUPPORTED MINING METHODS Pan
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14 Artificially supported mining me
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ARTIFICIALLY SUPPORTED MINING METHO
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Figure 14.2 Simplified view of stru
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Figure 14.5 Confined block model fo
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Figure 14.7 Crown and sidewall stre
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Figure 14.10 Sublevel open stoping
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Figure 14.12 Some applications of c
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15 Longwall and caving mining metho
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Figure 15.2 Shear stress drop in th
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LONGWALL AND CAVING MINING METHODS
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Figure 15.6 Hydraulic prop reaction
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Figure 15.7 Development and extract
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Figure 15.8 Vertical stress redistr
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Figure 15.11 Distribution of observ
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Figure 15.13 Plan view of microseis
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Figure 15.16 Ground-support interac
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Figure 15.18 Roadway support and re
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Figure 15.25 Comparison of isolated
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Figure 15.26 Geometry of a sublevel
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Figure 15.28 Theoretical determinat
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Figure 15.31 Deterioration of a cro
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Figure 15.32 Distinct element simul
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Figure 15.34 Extended Mathews stabi
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Figure 15.36 Comparison of postand
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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 499 and 500: LONGWALL AND CAVING MINING METHODS
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
Page 507 and 508: Figure 16.6 (a) Rectangular block g
Page 509 and 510: MINING-INDUCED SURFACE SUBSIDENCE f
Page 511 and 512: Figure 16.8 Relation between stope
Page 513 and 514: MINING-INDUCED SURFACE SUBSIDENCE M
Page 515 and 516: MINING-INDUCED SURFACE SUBSIDENCE
Page 517 and 518: Figure 16.14 Chart developed to est
Page 519 and 520: Figure 16.16 Progressive hangingwal
Page 521 and 522: Figure 16.19 Idealised model used i
Page 523 and 524: Figure 16.21 Longitudinal section,
Page 525 and 526: MINING-INDUCED SURFACE SUBSIDENCE t
Page 527 and 528: MINING-INDUCED SURFACE SUBSIDENCE w
Page 529 and 530: MINING-INDUCED SURFACE SUBSIDENCE F
Page 531 and 532: Figure 16.25 Subsidence troughs pre
Page 533 and 534: Figure 16.28 Predicted and measured
Page 535 and 536: 17 Blasting mechanics 17.1 Blasting
Page 537 and 538: Figure 17.1 An empirical matching o
Page 539 and 540: Figure 17.2 A finite difference mod
Page 541 and 542: Figure 17.4 Reflection of a cylindr
Page 543: BLASTING MECHANICS means that no ci
Page 547 and 548: Figure 17.9 Influence of field stat
Page 549 and 550: Figure 17.11 Generation of surface
Page 551 and 552: BLASTING MECHANICS The components o
Page 553 and 554: BLASTING MECHANICS amplitudes of th
Page 555 and 556: BLASTING MECHANICS 17.9 Evaluation
Page 557 and 558: Figure 17.15 (a) Schematic cross se
Page 559 and 560: BLASTING MECHANICS in Figure 17.17,
Page 561 and 562: MONITORING ROCK MASS PERFORMANCE (a
Page 563 and 564: MONITORING ROCK MASS PERFORMANCE su
Page 565 and 566: MONITORING ROCK MASS PERFORMANCE Ta
Page 567 and 568: Figure 18.2 The Distometer ISETH, a
Page 569 and 570: Figure 18.5 Self-inductance multipl
Page 571 and 572: MONITORING ROCK MASS PERFORMANCE is
Page 573 and 574: Figure 18.9 Biaxial vibrating wire
Page 575 and 576: MONITORING ROCK MASS PERFORMANCE me
Page 577 and 578: Figure 18.12 Cross section at 6650N
Page 579 and 580: Figure 18.13 Examples of convergenc
Page 581 and 582: Figure 18.15 Longitudinal section l
Page 583 and 584: Figure 18.16 (Cont.) MONITORING ROC
Page 585 and 586: Appendix A Basic constructions usin
Page 587 and 588: Figure A.3 Determining the angle be
Page 589 and 590: APPENDIX A USE OF HEMISPHERICAL PRO
Page 591 and 592: APPENDIX B STRESSES AND DISPLACEMEN
Page 593 and 594: 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
Page 615 and 616:
REFERENCES Gustafsson, P. (1998) Wa
Page 617 and 618:
REFERENCES Hood, M. and Brown, E. T
Page 619 and 620:
REFERENCES Kaiser, P. K. and Tannan
Page 621 and 622:
REFERENCES Lorig, L. J. and Brady,
Page 623 and 624:
REFERENCES Ortlepp, W. D. (1994) Gr
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REFERENCES Rojas, E., Molina, R. an
Page 627 and 628:
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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