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PREFACE TO THE SECOND EDITION. IN this Edition there has been added miscellaneous matter in the Addenda relating to the following subjects: Crater Forms and the Influence of Flexure thereon; Prof. Hofer's Theory of Blasting and Military Mining; Relation of Explosive Force to Resistance of Rock; The Best or Most Economical Length of Borehole Charge; Safety Explosives; and a Special Article to demonstrate the wrong premises on which Prof. Hofer's Theory of Blasting is based. THE AUTHORS. Preface It is a remarkable fact that the theories of rock blasting which have been generally adopted, do not take into account the influence of the form of the chamber employed, seeing that the initial force of the blast, and the resistance of the rock will largely depend thereon for any direction of the line of resistance. The methods by which the rules and formulae were deduced are fully explained, and examples of all the more important calculations are given to assist the engineer to deal with any question that may arise in practice, especial attention being directed to how the greatest economy may be attained in the boring of holes and consumption of explosive. The subject may be appropriately divided into two parts, viz. (1) the principles and their general application, and (2) appliances for drilling the shotholes, and methods of blasting in mines, quarries, tunnels and subaqueous operations. We have therefore treated it under these headings, this volume comprising the first part, whereas the second part will be published in a second volume which is in preparation. Valuable practical information is given on the most useful and economical explosives, and on detonators, electric fuses and electric exploders, for which we have much pleasure in acknowledging our obligations to Messrs. NOBEL'S EXPLOSIVES Co., LIMITED; Messrs. THE COTTON POWDER Co.; Messrs. CURTIS AND HARVEY; and Messrs. SIEMENS BROS. AND Co., LIMITED. We are also greatly indebted to Messrs. BICKFORD, SMITH AND Co. for information respecting their fuses. The information on electric blasting agrees with the results obtained in our experience, and will, we believe, be found very useful. A number of Tables are added to facilitate the calculations. The present volume, though only the first installment of the work, is complete in itself, and we believe it will be found to give the essential information for carrying out economical and systematic blasting operations. To render it more useful an Index is added which has been carefully prepared. It will be a source of great pleasure and satisfaction to us if we have accomplished the purposes for which this work was undertaken, namely, to give the Engineer, Miner and Quarryman a correct theory of rock blasting as well as a useful counselor in questions of application; to the teacher of the science a serviceable text-book for instruction; and to the student of mining and quarrying a welcome aid in the study of blasting. ALBERT W. DAW. ZACHARIAS W. DAW. Contents CHAPTER I. PRELIMINARY REMARKS. 1. Definition of rock blasting 2. Failure of previous rules for rock blasting 3. Operations of rock blasting 4. Effect of a blast 5. Conditions that influence a blast 6. Form of cavity produced in homogeneous rock 7. Quarrying of rock 8. Formula for determination of charge 9. Previous theories of rock blasting 10. Objections to Andree's and Guttmann's theories CHAPTER II. ON THE RESISTANCES IN ROCK BLASTING. 11. Different resistances to a blast 12. Influence of mode of application of force 13. Force of an explosion in a chamber conducive to rupture by shearing 14. Force required to produce rupture by shearing 15. Experiments on resistance of ice to rupture Table of experiments on resistance of ice to rupture 16. Similarity between cavities produced by sudden and gradual application of force 17. Force required to overcome the cohesive resistance of rock when there is one or more free faces 18. The resistances to rupture and shearing may be equalised 19. The section of rock which may be ruptured is proportional to periphery of chamber for a given line of resistance. 20. Economy of low explosives 21. Resistance of the mass after rupture 22. Resistance of the mass or weight of rock blasted at any angle to the horizon 23. Resistance of the friction and hanging of the rock along the line of rupture 24. Combined resistance of the weight and cohesion of rock 25. The resistance of cohesion of rock to rupture in blasting, varies as the square of the line of resistance CHAPTER III. FORCE DEVELOPED BY A BLAST. 26. Conditions affecting the force of an explosion 27. Of different action of explosives 28. Maximum pressures developed by explosives 29. The useful work of explosives 30. Calculation of power of an explosive 31. Relative force developed by an explosive 32. Condition necessary for the development of the maximum pressure of an explosive 33 Influence of the form of chamber, and the thermal conductivity of the rock on the charge CHAPTER IV. WEIGHT OF CHARGE REQUIRED TO EJECT ROCK AFTER RUPTURE. 34. Ratio of charge to mass of rock to be moved 35. Ratio of charge to line of resistance for similar masses of rock 36. Theory of the action and force of a blast after rupture has taken place 37. Sectional area of chamber required at right angles to line of resistance 38. Chamber coefficient CHAPTER V. RELATIONS OF THE DIAMETERS OF BOREHOLES AND SPHERICAL CHAMBERS TO LINES OF RESISTANCE. 39. Boreholes and chambers parallel to free face 40. Boreholes angled to a single exposed free face CHAPTER VI. ON THE MAXIMUM DISTANCE APART THAT SIMILAR SHOTHOLES, WHEN IN LINE PARALLEL TO A FREE FACE, WILL DISLODGE THE WHOLE OF THE ROCK BETWEEN THEM, WHEN FIRED SIMULTANEOUSLY, THE LINE OF RESISTANCE FOR EACH HOLE BEING THE SAME AS IF IT WERE TO BE FIRED INDEPENDENTLY, AND THE LINE OF RESISTANCE FOR TWO OR MORE SHOTHOLES SUPPORTING EACH OTHER. 41. Maximum distance which shotholes should be placed apart in strong and homogeneous rock 42. Influence of the cohesive strength of rock 43. Line of resistance for the combined shearing force of any number of similar shotholes equidistant from each other in line parallel to a free face 44. Economy of firing several similar charges close together in line parallel to a free face CHAPTER VII. QUANTITY OF ROCK WHICH WILL BE LOOSENED UNDER THE USUAL CONDITIONS OF BLASTING OPERATIONS WHEN THERE ARE NO JOINTS OR FISSURES. 45. Usual method of excavating rock by blasting 46. Form of craters 47. Angle of lines of rupture 48. Volume of rock dislodged when there are two free faces at right angles to each other 49. Volume of rock dislodged when there are three or four free faces at right angles to each other 50. Volume of rock dislodged by any number of similar shotholes in a step of rock 51. Volume of rock blasted by a concentrated charge 52. Simultaneous and consecutive firing CHAPTER VIII. THE LENGTH OF CHARGES IN BOREHOLES FOR RUPTURE BY SHEARING. 53. Charges for shearing 54. Influence of form of chamber on shearing force of charge 55. The length of charge in boreholes should be a constant multiple of the diameter for shearing CHAPTER IX. THE BEST POSITION FOR A CHAMBER OR CHARGE, WHEN THERE ARE TWO OR MORE FREE FACES AT RIGHT ANGLES TO EACH OTHER. 56. Principle on which the best position for a chamber may be determined 57. Rule for determining distance of chamber from free faces 58. Main lines of rupture 59. Irregular faces of rock CHAPTER X. BOREHOLE CHARGES. 60. Formulas for weight of borehole charges CHAPTER XI. THE INFLUENCE OP FISSURES, JOINTS AND BEDDING PLANES IN DETERMINING THE CHARGE. 61. Favourable conditions for quarrying operations 62. Rupture without shearing. The resistance to rupture of any section of rock limited by joints or free faces 63. Length and position of charge for shearing in beds of rock CHAPTER XII. BLASTING IN CUTTINGS, STOPES OR QUARRIED 64. Placing of shotholes in cuttings or stopes 65. Irregular surface line of rock 66. Joints CHAPTER XIII. THE PLACING OF SHOTHOLES WHEN THERE IS ONLY A SINGLE EXPOSED SURFACE FOR ATTACK, AND NUMBER OF SHOTHOLES REQUIRED FOR A HEADING OR SHAFT. 67. Removal of an entering portion of rock 68. Arrangement of holes in headings or shafts 69. Number of breaking-in shots required 70. Side cut 71. Bottom cut 72. Formulae for determining the number of shotholes required for headings or shafts CHAPTER XIV. HOW TO FIND THE COEFFICIENT OF ROCK Ca AND CHARGING COEFFICIENT Cv BY TRIAL SHOTS. 73. Trial shots no 74. Coefficient of rock Ca 75. Charging coefficient Ca CHAPTER XV. THE TAMPING OR STEMMING OF SHOTHOLES. 76. Results of Sir J. F. Burgoyne's experiments 77. Length of tamping required for powder charges 78. Tamping for high explosives CHAPTER XVI. ON THE DIFFERENT METHODS OF ARRANGING BOREHOLES IN DRIVING AND SINKING. 79. Systems of placing holes for driving and sinking 80. Diameter of holes 81. Best length for an advance in a heading, level or shaft 82. Key-holes 83. Centre cut in a heading 84. Square cut in a heading 85. Side cut in headings 86. Square cut in a shaft or rise 87. Centre cut in a circular shaft 88. Diagrams of holes for headings or shafts CHAPTER XVII. SAFETY FUSE. 89. Advantages of safety fuse 90. Principal kinds of fuse 91. Applications of the different fuses 92. Method of using fuses 93. Selection of fuses for different climates 94. Storing of fuses 95. Fuse-lighter for collieries 96. Volley-firer and instantaneous fuse CHAPTER XVIII. ELECTRIC SHOT FIRING. 97. Advantages of electric firing 98. High and low tension electricities for electric firing 99. High tension batteries 100. Low tension batteries 101. High and low tension detonators and exploders 102. Selection of electric fuses and battery or exploder 103. Choice of suitable leading wires and cables 104. Precautions to be taken to ensure insulation of joints and wires 105. Testing low tension fuses with galvanometer 106. Fitting of electric detonator fuse to charge 107. Connecting of wires to fuses for firing in series or parallel 108. Directions for use of exploders 109. Points to be attended to in electric blasting CHAPTER XIX. ON EXPLOSIVES AND THEIR SELECTION FOR ROCK BLASTING. 110. Qualities of a good explosive 111. List of explosives for rock blasting 112. High and low explosives 113. Influence of the strength and density of an explosive on the cost of boring holes 114. Valuable quality for an explosive 115. Methods of reducing the shattering effect of the high explosives 116. Advantages of gunpowder 117. Relation between the maximum lines of resistance which may be blasted in homogeneous rock with shotholes of one diameter charged with different explosives, and the maximum pressures developed by such explosives 118. Explosives most generally employed for rock and coal blasting 119. Dynamite 120. Detonators 121. Gelignite 121. Gelatine dynamite 123. Blasting-gelatine 124. Tonite 125. Blasting amberite 126. Electronite 127. Ordinary gunpowder 128. Compressed gunpowder in pellet blasting cartridges 129. Safety explosives Ardeer powder Carbonite Ammonite Bellite 205 Roburite No. 3 Dahmenite A Electronite No. 2 Westfalite CHAPTER XX. INSTRUCTIONS FOR THE USE OF EXPLOSIVES. 130. Directions for using dynamite, blasting gelatine, gelatinedynamite and other gelatine explosives 131. Directions for using tonite 132. Directions for using electronite and blasting amberite 133. Directions for loading a borehole with miner's coarse ordinary blasting-powder 134. Directions for using the nitrate of ammonia class of safety explosives CHAPTER XXI. 135. RECAPITULATION AND NOTATION OF THE MOST IMPORTANT FORMULAE CHAPTER XXII. EXAMPLES OF ALL THE MORE IMPORTANT CALCULATIONS THAT ARE LIKELY TO OCCUR IN THE DAILY PRACTICE OF ROCK BLASTING, AND OF THE USE OF THE TABLES FOR FACILITATING THE CALCULATIONS. 136. Example 1. Line of resistance, depth of borehole and charge 137. Example 2. Blasting a bench of rock 138. Example 3. Height of step or bench of rock 139. Example 4. Charging coefficient and volume of rock 140. Example 5. Economy of proportioning depth and diameter of borehole to height of bench of rock 141. Example 6. Maximum distance between shotholes fired simultaneously 142. Example 7. Line of resistance for two shotholes supporting each other 143. Example 8. Economy of shotholes supporting each other 144. Example 9. .Economy of firing shotholes simultaneously 145. Example 10. Number of shotholes required to unkey a face of rock 146. Example 11. Line of resistance and charge in a bed of rock 147. Example 12. Position, depth and diameter of boreholes in jointed rock 148. Example 13. Number of shotholes required for a heading 149. Example 14. Position and size of chambers, and charge for a large or giant blast 150. Example 15. Range of consumption of explosives in quarries, tunnels and mines TABLES. I. Maximum lines of resistance for charges in boreholes II. Charges for boreholes III. Depths of boreholes for shearing IV. Lines of resistance for two, three and four shotholes supporting each other V. Lines of resistance for angled boreholes VI. Approximate volumes of rock blasted by concentrated charges VII. Approximate volumes of rock which will be blasted by single shotholes in the case of stepped workings and two free faces VIII. Approximate volumes of rock which will be blasted by single shotholes in the case of stepped workings and three free faces IX. Approximate volumes of rock which will be blasted by single shotholes in the case of stepped workings and four free faces X. Approximate volumes of rock which will be blasted by two and three similar shotholes placed a distance 2 W apart, and fired simultaneously in the case of stepped workings and two free faces XI. Sections of rock which will be blasted by borehole charges having a length = 12 d XII. Capacity of i foot of borehole in cubic inches XIII. Weight of a lineal foot of round, octagonal and square drilling steel XIV. Useful hydraulic data XV. Weight of stone and mineral substances XVI. Comparison of imperial and metric systems XVII. Pressures of atmospheres in Ibs. per square inch XVIII. Decimal equivalents of an inch XIX. Properties of the circle INDEX End of Preview.
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