Rock Fragmentation

8/10/2019 Rock Fragmentation

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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


5/18

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

Rock Fragmentation

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