Post on 02-Jun-2018
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Rock Fragmentation
Oleh:
Dr. Singgih Saptono
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Fragmentation
A blasted rock muckpile and the fragment sizes within it arevery important for the mining industry since they affectthe downstream processes from hauling to grinding.
The size distribution of the blasted muckpile can be
predicted by a variety of semi empirical models which arebased on blast design parameters, such as burden, spacing,drillhole diameter, bench height and explosivesconsumption.
It has been the experience of many researchers that these
models are quite successful in predicting the meanfragment size; however they lack accuracy in predicting the80% passing size used in comminution calculations.
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A simple diagrammatic
presentation of
Drill to Mill fragmentationflow sheet
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Mechanism of breakage by flexion
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Potential problems related to stiffness ratio
The ratio of bench height (H) to effective firing burden (Be) represents
the stiffness ratio in a surface mine bench blast.
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Fragmentation
Good fragmentation with good
uniformity inside the muckpile
Poor fragmentation with boulders inside
the muckpile
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Uncontrollable factors
Uncontrollable parameters concerning blast
design are
The rock mass properties and
The geological structure
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These factors also influence the blast design
parameters and the fragmentation produced; thustheir effects to blasting need to be quantified
(Tandanand, 1973; Hustrulid, 1999) .
Rock factor
A = 0.06*(RMD + JF + RDI + HF)
where RMD is the mass description, JF is the joint
factor, RDI is the rock density influence and HF is the
hardness factor. Details on the model can be found
in Cunninghams publication (Cunningham, 1987).
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Controllable factors
A- Geometric: Diameter, charge length, burden,
spacing etc.
B- Physicochemical or pertaining to explosives:
Types of explosives, strength, energy, priming
systems, etc.
C- Time: Delay timing and initiation sequence.
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Geometric parameters are actually influenced byuncontrollable and controllable factors,
(i) Diameter (d) and Depth of Drillhole (di).
(ii) Inclination (di) and Subdrilling Depth (SUB) of Drillhole.
(iii) Height (ls) and Material of Stemming.
(iv) Bench Height (Hb).
(v) Spacing to Burden Ratio (mb).(vi) Blast Size, Direction and Configuration.
(vii) Initiating Sequence and System.
(viii) Buffers and Free Faces.
(ix) Explosive Type, Energy and Loading Method.
(x) Powder Factor q =Q/Vo where Q is the total quantity of explosiveper borehole and V is the total volume of rock blasted.
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Fragmentation Models
Particle sizing
Gates-Gaudin-Schumann function
Where y is the fraction of the muckpile with particle size smaller than x, n
is a distribution parameter and ksis the maximum particle size.
Rosin-Rammler equation
where b is a constant.
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The Rosin-Rammler equation has been used by
Cunningham for blasting analysis
where R is the fraction of material retained on a screen, x is the screensize, xc is a constant, called the characteristic size, and n is the uniformity
index.
The uniformity index, typically, has values from 0.6 to 2.2. The value of n
determines the shape of a curve. A value of 0.6 means that the muckpile is
non uniform (dust and boulders) while a value of 2.2 means a uniform
muckpile with the majority of fragments close to the mean size (Clark,
1987).
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These equations are often used in combination with
Kuznetsovs equation,which is expressed in terms of the quantity of explosive per
blasthole, Qe and the relative to ANFO weight strength of
explosives, EANFO and the powder factor, q = Q/Vo.
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The following parameters are related
to muckpile uniformity.
(i) Distribution of explosive in the blast
(burden, spacing to burden ratio, borehole
diameter, collar, subgrade, bench height)
(ii) Firing accuracy of detonators used
(iii) Timing of detonators used
(iv) In situ fragmentation due to geological
discontinuities
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Cunningham expressed the uniformity index n by
where B is the burden in m, d is the hole diameter in mm, Dt is the
standard deviation of drilling accuracy in m, mb is the spacing to burden
ratio, lcb is the charge length above grade level in (m) and Hb is the bench
height in (m).
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where BL is the bottom charge length above grade (m), CL isthe column charge length (m), and lcbis the total charge
length above grade. (Cunningham, 1987)
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Where C(n ) is a correction factor used to calibrate the model if data
are available and ns is a factor incorporating scatter of the delay times
used in the blast. The factor nscan be expressed as follows:
With st being the standard deviation of the
initiation system and Tx the desired delay
time between holes.
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Kuz-Ram model