Rock Drilling
Drilling, in the field of rock excavation by drilling and blasting, even for excavation by non-blasting method, is the first and essential operation. The drilling mechanism, rock drillability and its classification, different drilling methods, equipment,
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Rock Drilling
Drilling, in the field of rock excavation by drilling and blasting, is the first and essential operation carried out, and its purpose is to drill holes, with the adequate geometry and distribution within the rock masses, where the explosive charges will be placed along with their initiating devices. Even in the rock excavation with non-blasting method, drilling sometimes is also needed for creating some spaces to place the chemical expanding agent or insert a breaking tool or only creating a free face for rock breaking by mechanical tools. The systems of rock drilling have been developed with various means such as mechanical methods (percussion, rotary, rotary-percussion), thermal method (flame, plasma, hot fluid, freezing), hydraulic method, sonic method, and laser ray method. Nevertheless, mechanical drilling system is always the most economic and convenient method and widely used in mining and civil engineering field at present. Therefore, in this book, only the mechanical means will be discussed.
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Mechanism of Rock Breakage by Drilling and Drillability of Rock Mechanism of Rock Breakage During Drilling
The general types of rock breakage during drilling by mechanical method, including percussion drilling, rotary drilling, and rotary-percussion drilling, are three kinds of basic mechanism: percussion-penetration, pressured roller, and cut (see Fig. 2.1). During the process of drilling the tool (percussive drilling bit, roller-disk and studded roller-disk cutter, rotary tricone bit, or drag tools), the first action is push
© Metallurgical Industry Press and Springer Science+Business Media Singapore 2017 D. Zou, Theory and Technology of Rock Excavation for Civil Engineering, DOI 10.1007/978-981-10-1989-0_2
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2 Rock Drilling
Fig. 2.1 General types of rock breakage during drilling: a percussive-penetration; b pressured roller; c cut
Fig. 2.2 Rock breakage by tool penetration
(or percussion), the tool penetrates into (indentation) and breaks (by Fp) the rock surface, then expands the breakage by continual percussion together with rotation of the bit, or pressured-rolling by thrust force (Fp) and torque (M) or continual cut by push force (Fr) under the thrust force (Fp). The tool penetrates and breaks the rock surface by a static (thrust) force or impact (percussion) force; this is the basic process of the rock breakage by mechanical method. The process of tool penetrating the rock surface can be divided into four phases as follows [1] (Fig. 2.2): • Crushed zone As the tool tip begins to dent the rock surface, stress grows with the increasing load and the material is elastically deformed, zone III in Fig. 2.2. At the contact surface, irregularities are immediately formed and a zone of crushed rock powder core develops beneath the indenter (the bottom or insert of the tool). The crushed core comprises numerous microcracks that pulverize the rock into powder of extremely small particles. About 70–85 % of the indenter’s work is consumed by the formation of the crushed zone. The crushed c
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