24722484 education drilling and blasting docs143
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Drillability of a rock depends on
hardness of its constituentminerals.
grain sizecoarse-grained structure is easier todrill
crystal form. minerals with highsymmetry
abrasive
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Rocks are classified into threemain groups
Igneous or magmatic rocks(formed from solidified lava or "magma").
Sedimentary rocks (formed by
deposition of broken material or bychemical precipitation).
Metamorphic rocks (formed by thetransformation of igneous or sedimentary
rocks, in most cases by an increase inpressure andheat).
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Igneous rock
Depending on whether the magmasolidifies at depth, or as a dyke rock,or on the surface, the rock is givendifferent names even if thecomposition is the same.
plutonic rock: magma solidifies deep
down in the earth's crust. dyke rock: magma rises towards thesurface.
volcanic rock: on the surface.
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Sedimentary rocks
deposition of material bymechanical or chemical actionand a consolidation of this
material under the pressure ofoverlying layers.
also arise as a result of the
chemical precipitation ofminerals or by proliferation oforganic organisms
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Rock classification
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Rock Strength
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Fracture Mechanics
strength of brittle materials is theirability to break by crackpropagation.
tensile strength of these materials isso much lower than the compressivestrength.
stress concentration in front of the
crack tip stress intensity factor KI is a
function of the crack length and the
load o
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The critical value of KI when the crack just startsmoving is amaterial constant KIC.
The work done per unit new cracksurface is GIC which is coupled to KIC through therelation:
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Abrasiveness
The factors that enhance abrasive capacities ofrocks are the following: The hardness of the grains of the rock. The rocks
that contain quartz grains are highly abrasive. The shape of the grains. Those that are angular are
more abrasive
than the round ones. The size of the grains. The porosity of the rock. It gives rough contact
surfaces with localstress concentrations.
The heterogeneity. Poly mineral rocks, althoughthese are equally hard,are more abrasive because they leave rough surfaces
with hard grainsas, for example, quartz grains in a granite.
R k M St th d
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Rock Mass Strength andStructure
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Rock BreakingProcesses
Primary
b k ld
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Primary breakage processes wouldinclude the following
Impact or hammering.
Percussive drilling.
Button type cutters for raiseand tunnel borers
Disc type cutters for raiseand tunnel borers.
Drag bit.
Diamond bits.
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Theory
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Tertiary breakage processesinclude:
1. Breaking boulders by impactor mud blasting
2. Crushing 3. Milling
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sce aneous
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sce aneous
Thermal spalling
Water jets.
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