| CHAPTER I. The Tools,Machines, and other Appliances used in Rock Blasting. | |
| PAGE | |
| Section I. Hand-boring Tools.—Drills. Hammers. Auxiliary Tools. Sets of Blasting Gear | [1] |
| Section II. Machine-boring Tools.—Machine Rock-drills. Borer-bits. Drill Carriages | [23] |
| Section III. Appliances for firing Blasting Charges.—Squibs. Safety Fuse.Electric Fuses. Cables. Detonators. Electric Firing-Machines | [42] |
| CHAPTER II. Explosive Agentsused in Rock Blasting. | |
| Section I. Phenomena accompanying an Explosion.—Nature of an Explosion. Heatliberated by an Explosion. Gases generated by an Explosion. Force developed by an Explosion | [64] |
| Section II. Nature of Explosive Agents.—Mechanical Mixtures. Chemical Compounds | [76] |
| Section III. Relative Strength of the common Explosive Agents.—Force developedby Gunpowder. Relative Force developed by Gunpowder, Gun-cotton, and Nitro-Glycerine | [88] |
| Section IV. Means of firing the common Explosive Agents.—Action of Heat. Detonation | [92] |
| Section V. Some Properties of the common Explosive Agents.—Gunpowder,Gun-cotton, Dynamite. Firing Temperatures | [97] |
| Section VI. Some Varieties of the Nitro-Cellulose and the Nitro-GlycerineCompounds.—Nitrated Gun-cotton. Tonite, or Cotton-Powder. Schultze’s Powder. Lithofracteur.Brain’s Powder. Cellulose-Dynamite | [103] |
| CHAPTER III. The Principles of Rock Blasting. | |
| Line of least Resistance. Force required to cause Disruption. Conditions of Disruption.Example of a Heading. Economical Considerations. Tamping | [106] |
| CHAPTER IV. The Operations ofRock Blasting. | |
| Hand Boring.—Boring the Shot-holes. Charging the Shot-holes. Firing the Charges | [128] |
| Machine Boring.—Boring the Shot-holes. Charging and Firing. Removing the dislodged Rock.Division of Labour | [142] |
| Examples of Drivings.—The St. Gothard Tunnel. The Hoosac Tunnel. The MusconetcongTunnel. Headings at Marihaye, Anzin, and Ronchamp | [157] |
| CHAPTER V. Subaqueous Blasting. | |
| Preparation of the Charge. Boring under Water. Submarine Rocks. Obstructions in Water-courses | [164] |
ROCK BLASTING.
CHAPTER I.
THE TOOLS, MACHINES, AND OTHER APPLIANCES USED IN BLASTING ROCKS.
Section I.—Hand Boring.
Drills.
—The operations of blasting consist in boring suitable holes in the rock to be dislodged, in inserting a charge of some explosive compound into the lower portion of these holes, in filling up, sometimes, the remaining portion of the holes with suitable material, and in exploding the charge. The subjects which naturally first present themselves for consideration are: the nature, form, and construction of the tools, machines, and other appliances used. Of these tools, the “drill” or “borer” constitutes the chief. To understand clearly the action of the rock drill, we must consider the nature of the substance which has to be perforated. He who has examined the mineral constitution of rocks will have recognised the impossibility of cutting them, using that term in its ordinary acceptation, inasmuch as the rock constituents are frequently harder than the material of the tools employed to penetrate them. As a rock cannot be cut, the only way of removing portions of it is to fracture or to disintegrate it by a blow delivered through the medium of a suitable instrument. Each blow so delivered may be made to chip off a small fragment, and by this means the rock may be gradually worn away. To effect this chipping, however, the instrument used must present only a small surface to the rock, in order to concentrate the force, and that surface must be bounded by inclined planes or wedge surfaces, to cause a lateral pressure upon the particles of rock in contact with them. In other words, the instrument must be provided with an edge similar to that possessed by an ordinary cutting tool.
The conditions under which the instrument is worked are obviously such that this edge will be rapidly worn down by attrition from the hard rock material, and by fracture. To withstand these destructive actions, two qualities are requisite in the material of which the instrument is composed, namely, hardness and toughness. Thus there are three important conditions concurring to determine the nature and the form of a cutting tool to be used in rock boring—1, a necessity for a cutting edge; 2, a necessity for a frequent renewal of that edge; and 3, a necessity for the qualities of hardness and toughness in the material of the tool.
In very hard rock, a few minutes of work suffice to destroy the cutting edge, and then the tool has to be returned to the smithy to be re-sharpened. Hence it is manifest that the form of the edge should not be one that is difficult to produce, since, were it so, much time would be consumed in the labour of re-sharpening. Experience has shown that the foregoing conditions are most fully satisfied in the steel rod terminating in a simple chisel edge, now universally adopted.