BREAKAGE AND FRAGMENTATION MODELLING FOR UNDERGROUND PRODUCTION BLASTING APPLICATIONS 27th Mining Convention Arequipa, Peru 12 to 16 September, 2005 Dr. Italo Oñederra Senior Project Engineer – Mining Julius Kruttschnitt Mineral Research Centre The University of Queensland Isles Road, Indooroopilly Queensland, Australia 4068 Tel. + 61 7 3365 5979 Fax +61 7 3365 5999 email: [email protected]
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Breakage and Fragmentation Modelling for Underground (Onederra-Extemin05)
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3. FRAGMENTO – “A NEW FRAGMENTATION MODELLING FRAMEWORK FOR UNDEGROUND PRODUCTION BLASTING APPLICATIONS” ....................................7
4. EVALUATION OF THE SINGLE RING MODELLING COMPONENT .......................8
4.1. Model response to changes in geometry and charging conditions...................8 4.2. Fragmentation uniformity versus burden curves............................................14
5. APPLICATION OF THE SINGLE RING MODELLING COMPONENT ....................17
5.1. Fragmentation uniformity versus burden from SLC configurations.................17 5.2. Fragmentation modelling and uniformity analysis of inclined undercut rings..17
Figure 1. Parameters of hangingwall ring blast - base case scenario for model evaluations....................................................................................................9
Figure 2. Uniformity index versus burden for a two hole ring blast in a simulated hard competent rock ...........................................................................................14
Figure 3. Uniformity index versus burden curves for a range of diameters in the simulated two-hole ring blast.........................................................................16
Figure 4. Example of design and model input parameters for the 5330 UCL, 9 hole ring layout ..........................................................................................................16
Figure 5. Fragmentation uniformity analysis of 9-hole SLC layout..............................17
Figure 6. Drilling and charging parameters for inclined undercut rings .......................18
Figure 7. Critical burden conditions for inclined five-hole leading and lagging rings.....19
Figure 8. Fragmentation modelling of 89 mm inclined undercut ring ...........................20
Figure 9. Results of fragmentation uniformity analysis to identify critical burden ........21
List of Tables
Table 1. Sensitivity of fragmentation predictions to changes in geometry..................10
Table 2. Sensitivity of fragmentation predictions to changes in explosive charging characteristics.............................................................................................12
Table 3 Mechanical and breakage properties for the NPM E26 Lift 2 orebody ..........18
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ABSTRACT
A review of breakage and fragmentation literature has shown that only a few models have
been specifically developed for applications in underground production blasting. These
approaches, however, have applied empirical relations that do not adequately consider ring
blasting geometries, have failed to appropriately respond to changes in basic design input
parameters, and have complex input and calibration requirements. This justified the
development of an alternative modelling framework to specifically address the prediction of
fragmentation in underground production blasting. The new model, designated as
“FRAGMENTO”, is introduced in this paper. The basis of FRAGMENTO is a “single ring”
deterministic model which can be extended into a stochastic model to simulate the impact of
external operational factors on fragmentation. The single-ring component mechanistically
models the extent of both near field and mid to far field fracture zones to predict the
distribution of rock fragments expected to report to drawpoints. In this paper the response of
this key component is evaluated and its practical application demonstrated with the
introduction of a methodology to infer critical burden conditions. FRAGMENTO can be used
at the evaluation stage of blast design in an operating mine and for studies at the conceptual,
pre-feasibility and feasibility stages of a project, where different drill and blast scenarios and
associated costs are assessed.
1. INTRODUCTION
The first stage of the comminution process in metalliferous mining is the breakage and
fragmentation of the rock mass, generally by drilling and blasting. This activity may have the
greatest leverage in the efficiency of a mining operation, as the product from a blast impacts
on every downstream operation (Grant et al, 1995). In the case of underground operations,
controlling both fragmentation and the degree of blast induced damage is an important aspect
of the mine design process. Poor drilling and blasting practices - typified by excessive over-
break, dilution, oversize fragmentation, restricted access and increased local reinforcement
requirements - contribute to increased mining cycle times and costs, and can have a negative
effect on the efficiency of mining activities as a whole (Singh, 1993 and Brown et al, 1994).
Within the underground mining cycle, the influence of drilling and blasting can be significant in
the key aspects of material flow, handling and processing (Klein et al, 2003). For example,
the impact of fragmentation on flow dynamics is considered critical in sub-level caving (SLC)
operations, as flow has been shown to be directly linked to recovery (Power, 2004).
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The design of underground production blasts (i.e. the ring geometries) commonly continues to
be defined by trial and error or the application of “rules of thumb”. With the application of
these approaches, it continues to be difficult, if not impossible, to make adequate predictions
at both the pre-feasibility and feasibility stages of a project. Hustrulid (2000) reinforces this
point by noting that, for the high levels of up-front capital expenditure, designs must function
as designed and the as-built must closely resemble the as-designed. For this reason
engineers, geologists, mine and plant managers must have access to accurate modelling and
simulation tools which can address every stage of the design process, allowing the
determination of appropriate and cost effective design parameters at the outset.
2. APPLIED FRAGMENTATION MODELLING
The need for engineering solutions to full-scale blasting problems has driven the development
of several fragmentation models. In the blasting literature these models can be classified into
three main groups: numerical, empirical and mechanistic (Dawes, 1986 and Wedmaier,
1992).
Numerical models continue to be developed from fundamental principles of rock fracture,
and have allowed the further development of theories that better describe explosive rock
breakage mechanics. Their application has, however, been restricted to the simulation and
analysis of small volumes consisting primarily of one or two blastholes; there is no evidence of
these approaches being directly applied to fragmentation modelling in underground ring
blasting conditions. The challenge of further development of these models is related to
continuous advances in non-ideal detonation modelling and geomechanical codes, such as
the Hybrid Stress Blasting Model (HSBM) (Cundall et al, 2001).
Empirical models are the simplest form of modelling and have been mainly developed by
linking standard design parameters (such as burden distance and hole spacing), with
fragmentation parameters (such as average fragment size, P50 or X50) (Bergmann et al,
1973). Arguably, the most popular and successful empirical based fragmentation models
have been those applicable to surface blasting, such as the Kuz-Ram and Kuznetsov based
models (Kuznetsov, 1973 and Cunningham, 1987). Their popularity is due to their simple
frameworks, with design variables that are familiar to the mine blast engineer (e.g. powder
factor, burden and spacing), making them easy to implement in computer programs.
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Applications of empirical methods to underground production blasting have been reported by
Stagg et al (1994), with the development of site specific formulae to predict fragmentation in
simple underground pattern geometries. More recently, applications by Adamson and Lund
(2001) and Trout (2002) have also been reported; these have been based on modified Kuz-
Ram modelling procedures developed at the JKMRC (Kanchibotla et al 1999 and Thornton et
al, 2001). However, the application of these approaches may be limited, as they do not
properly consider the three-dimensional distribution of explosive charges, which is
characteristic of the more complex geometries found in underground ring blasting.
Mechanistic models represent the next degree of sophistication in blasting models (Dawes,
1986). These models recognise a specific mechanism or series of mechanisms by which the
explosive fragmentation of rock is affected. Strictly speaking, these models are also
empirical but have a more complex and less “site specific” framework.
There have been three cases of mechanistic models being directly applied to underground
fragmentation modeling. They include the approach proposed by Kleine (1988) and coded
into the FRAGNEW program (Riihioja, 2004); the SABREX model developed by ICI
explosives and described by Kirby et al (1987); and the model proposed by Preston (1995)
embedded in the DynACAD-3D software package. The application of SABREX, and more
specifically the ICRAX component of this model, at the underground Denison Mine was
reported by Sheikh and Chung (1987). It should be noted that this modelling work was
restricted to blasting with parallel hole patterns. To date, there is no documented evidence of
this approach being further applied to more complex ring blasting geometries. The package
is proprietary to the ORICA explosives company.
The fragmentation models proposed by Kleine (1988) and Preston (1995) are the only ones
found in literature that have postulated original frameworks to model underground ring
blasting conditions. Of these two, Kleine’s is the only one that has been published in detail.
Kleine’s approach consists of the interaction of three independent models which address the
determination of in situ block size distributions, the calculation of vibration energy contributing
to breakage at pre-defined points in a volume of rock, and the application of comminution
theory to define the breakage characteristics of the rock at these points. With the exception of
Chitombo and Kleine (1987), there do not appear to be any other references to the application
of this particular model. It was recognised that calibration requirements were its main
disadvantage and the reason for the lack of acceptance in practice.
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Acknowledged criticisms and limitations of the model are associated with the vibration
energy component (Kleine et al, 1990). For engineering design purposes, a less
obvious, but what can be considered to be a critical limitation of Kleine’s approach,
has been its reported inadequate response or sensitivity to changes in ring burden
conditions (AMIRA/JKMRC, 1993), in addition to its inability to infer critical burden
conditions.
Following Kleine’s development, Preston (1995) reported the implementation of a
breakage and fragmentation model for underground ring blasting applications
embedded in a 3D blast analysis package called DynACAD-3D. Although
information regarding the modelling framework is limited, it appears that maximum
and minimum breakage envelopes are defined by a stress attenuation curve, which is
obtained from field measurements using pressure sensors in water-filled boreholes.
The model also appears to implement a modified Kuz-Ram function to calculate the
distribution of fragments from the breakage regions defined by each blasthole. An
example application of the model is discussed by Preston (1995) but no validation is
reported. In the example, the fragmentation curves appear to be derived from only
one distribution function (i.e. a Rosin-Rammler based function). Further review of this
approach is constrained by the lack of available information describing any further
application in underground production blasting.
The literature indicates that very little emphasis has been placed on the development
of fragmentation models that can be directly applied to underground production
blasting. While the JKMRC is involved in an international collaborative project
developing a more fundamental model of rock breakage, called the Hybrid Stress
Blasting Model (HSBM) (Cundall et al, 2001), work is continuing on the development
and improvement of empirical and mechanistic methods, based on observed
responses of rock masses to actual blasting. This is evident through the
development, evaluation and application of FRAGMENTO, an alternative modelling
framework to specifically address the fragmentation prediction problem in
underground production blasting.
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3. FRAGMENTO – “A NEW FRAGMENTATION MODELLING FRAMEWORK FOR
UNDEGROUND PRODUCTION BLASTING APPLICATIONS”
FRAGMENTO is a modelling framework specifically developed for underground production
blasting. The approach is aimed at the design evaluation stage in an operating mine, and for
studies at the conceptual, pre-feasibility and feasibility stages of a project, where different
drill and blast scenarios and associated costs are assessed. In FRAGMENTO, a “single ring”
component is proposed as the basis of the overall framework. This component is then
extended into a stochastic model that simulates the impact of external factors on
fragmentation, such as blasthole deviation, dislocation and overall detonation performance.
The single ring component models the extent of both near-field and mid to far-field fracture
zones to predict the distribution of rock fragments expected to report to drawpoints. Based
on findings by Gaidukov and Myzdrikov (1974), the fragmentation output is derived from the
combination of two Rosin-Rammler based functions, following an approach similar to that
adopted by Kanchibotla et al (1999). These two functions require the determination of three
modelling parameters: the fines cut off point (fc), the expected mean fragment size (X50) and
the “coarse” uniformity index (nc). Three original methodologies have been developed to
determine these key parameters.
• A new mechanistic model to estimate the proportion of fines generated during the
blasting process: for a given explosive charge and rock combination, the approach
predicts the proportion of crushed material from both the crushed and fractured
zones.
• An empirical approach to estimate the expected post-blast mean fragment size (X50):
this empirical method introduces a mean in situ block size parameter based on the
fracture properties of the rock mass. It also implements a three dimensional energy
density distribution model to determine a design specific fragmentation factor.
These two parameters are then applied to estimate the X50.
• A model to predict fragmentation uniformity: for a given blast and charging layout,
the approach implements a simple three dimensional peak particle velocity (PPV)
attenuation model that allows the determination of breakage and fragmentation
uniformity characteristics.
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To enable the evaluation, validation and application of the single ring component of
FRAGMENTO, all equations and algorithms have been encoded into the JKSimBlast
underground software package.
It is beyond the scope of this paper to demonstrate every component of FRAGMENTO. The
following discussions will focus mainly on the application and evaluation of the single ring
component. For further details, including validation and demonstrations of the proposed
stochastic modelling component, the reader is referred to Onederra (2004a & 2004b).
4. EVALUATION OF THE SINGLE RING MODELLING COMPONEN T
4.1. Model response to changes in geometry and char ging conditions
In this section, the response of the proposed single ring modelling component is evaluated
through simulations of the base case described in Figure 1. The analysis involves the
evaluation of ring geometry variations (including burden and average toe spacing), and ring
charging characteristics (including explosive density and two charges of differing densities).
The evaluation of these parameters was considered important for the model’s broader
application in design and analysis. Tables 1 and 2 summarise the results of the evaluations
for variations in ring geometry and charging conditions respectively.
Model Output (4000 mm/s) Critical point (4000 mm/s)Model Output (4500 mm/s) Critical point (4500 mm/s)
3 hole inclined leading ring 89 mm - Emulsion 1.0 g/cc
PPV breakage > 4000 mm/s
PPV breakage > 4500 mm/s
Pra
ctic
al d
esig
n bu
rden
(40
00
mm
/s -
mo
del)
Pra
ctic
al d
esig
n b
urd
en (
4500
mm
/s -
mod
el)
Bur
den
use
d
Figure 9. Results of fragmentation uniformity anal ysis to identify critical and
practical burden conditions for the adopted three h ole inclined undercut rings
6. CONCLUSIONS
Very little emphasis has been placed in the development of accessible fragmentation
modelling frameworks that can be directly applied to underground production blasting
environments. The few that have been developed have applied empirical relations that do not
adequately consider ring blasting geometries, have failed to appropriately respond to changes
in basic design input parameters, and have complex input and calibration requirements. This
justified the development of an fragmentation modelling framework specific to underground,
addressing the following key requirements:
• ability to predict breakage conditions and the full range of fragmentation expected to
report to drawpoints from knowledge of nominal blast design parameters and rock
mass characteristics;
• ability to simulate the likely impact on fragmentation by other key external factors such
as drilling quality or overall ring detonation performance;
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• ability to be applied in conceptual, pre-feasibility and feasibility stages of a potential
resource as well as at the engineering design and optimisation phases of an
operating mine.
The above requirements have been addressed with the development of FRAGMENTO. In
this paper the single ring component of FRAGMENTO was evaluated through a series of
simulations and demonstrated to respond adequately to variations in geometry and charging
conditions. The applicability of the model in blast design was also demonstrated with the
introduction of a methodology to infer critical burden conditions.
With any modelling approach however, there will always be some limitations associated with
its inherent assumptions, FRAGMENTO is no exception and these can be summarised
as follows.
• From the assumed breakage modelling mechanisms, drastic changes in explosive
compositions, that is, explosives outside the current range of commercially available
products could not be reliably modeled without site specific monitoring and
calibration trials. Approaches currently being developed which link non-ideal
detonation with geomechanical codes may provide a more robust platform to
address this limitation.
• Following current practice, the proposed framework only considers single-hole
sequential firing conditions. The impact of delay timing on breakage and
fragmentation has not been included at this stage. Although a factor that under
certain conditions may be important, its direct impact on fragmentation has been very
difficult to quantify and/or validate in situ and there is insufficient data to be included
in a mechanistic framework such as that proposed in this paper.
7. REFERENCES
Adamson, W R and Lund, A S, 2001. On the use of mechanistic blast-outcome measurement and modelling for optimisation of explosive selection in underground mining. Proceedings of EXPLO 2001, NSW, Australia. The Australasian Institute of Mining and Metallurgy, 207-223.
AMIRA/JKMRC, 1993. Advanced Blasting Technology P93E (1990-1993). Final Report. JKMRC, University of Queensland, Brisbane.
Bergmann, O R, Riggle, J W and Wu, F C, 1973. Model rock blasting: Effect of explosives
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properties and other variables on blasting results. Int J. Rock Mech. Min. Sci. and Geomech Abstr., 10: 585-612.
Brown, E T, Chitombo, G P, Li, T and Walker, P A, 1994. Rock Mass Damage in Underground Metalliferous Mines. The 1994 ISRM International Symposium. Integral Approach to Applied Rock Mechanics, Santiago , Chile, M. Van Sint Jan (Ed.), Volume I: 289-301.
Chitombo, G P and Kleine, T H, 1987. An engineered blast design philosophy for open stoping operations - A case study at Brunswick Mining and Smelting No. 12 Mine, Canada. Second international symposium on rock fragmentation by blasting, Keystone, Colorado, Society for experimental mechanics, 657-671.
Cundall, P, Ruest, M, Chitombo, G, Esen, S and Cunningham, C, 2001. The Hybrid Stress Blasting Model: A Feasibility Study. Confidential report. JKMRC, ITASCA and AEL.
Cunningham, C V B, 1987. Fragmentation estimations and the Kuz-Ram model - Four years on. Proceedings of the second international symposium on rock fragmentation by blasting, Keystone, Colorado, 475-487.
Dawes, J J, 1986. The study of blast performance and design in mining via the analysis of ground vibrations. PhD. Thesis, University of Queensland, Australia.
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Kirby, I J, Harries, G H and Tidman, J P, 1987. ICI's computer blasting model SABREX - Basic principles and capabilities. Proceedings of the 13th conference on explosives and blasting technique, SEE, Annual meeting, Miami Florida, 184-194
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Riihioja, K, 2004. Personal communication.
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Singh, S P, 1993. Prediction and Determination of Explosive Induced Damage. Rock Fragmentation by Blasting, Rossmanith (Ed.). Balkema, Rotterdam, 183-192
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Thornton, D, Kanchibotla, S and Esterle, J, 2001. A fragmentation model to estimate ROM distribution of soft rock types. Proceedings of the Twenty-Seventh Annual Conference on Explosives and Blasting Technique, ISEE, Orlando, Florida, USA, 41-53.
Trout, P, 2002. Production drill and blast practices at Ridgeway Gold Mine. Proceedings of the Underground Operators' Conference, The Australasian Institute of Mining and Metallurgy , Townsville , Australia, 107-117.
Wedmaier, R, 1992. An investigation of failure criteria and a blast wave propagation model for a description of the rock breakage problem. PhD Thesis, University of Queensland, Australia.