A Pattern For Improvement
Firing pattern and stemming column adjustments enhance blast performance at a limestone quarry in the Philippines
By Dr Piyush Rai, reader in mining engineering; Bhanwar Singh Choudhary, senior research fellow, Department of Mining Engineering, Institute of Technology, Banaras Hindu University, India; and F.L. Imperial, president, Republic Aggregate Co. Inc., the Philippines
A firing pattern is like an electrical circuit, providing a pathway for a detonation wave in order that explosive charges in the blastholes can be initiated. In any blasting programme the foremost requirement is sequential generation of free face (with the blast progression). To this end, the firing pattern determines the movement and direction of rock by creating free face for subsequent blastholes/rows. Extensive work has been reported by various researchers1,2,3 on different types of firing pattern (row-to-row, diagonal, V-type and skewed V-type). The researchers suggest that each firing pattern has its own application. Proper use of pattern in relation to the blast requirements can provide optimal blast performance in terms of fragmentation, throw, wall control etc. This is largely attributed to the importance of firing burden in any blast. By changing the firing pattern, the firing burden, and thereby the ratio of spacing to burden, is also subject to change4,5.
Stemming the upper section of a blasthole with inert material confines and retains the gases produced by the explosion within the hole. Confinement and retention promote rock fracturing by transmitting a major proportion of shock as well as gas pressure through the broken rock mass prior to the release of the stemming.
Improper confinement results not only in wastage of energy and poor fragmentation, but also in environmental problems such as airblast, flyrock etc6,7. According to Brinkmann8, almost 50% of explosive energy is lost if premature venting is allowed to occur through the collar region of the blasthole. Floyd9 indicated that improper explosive confinement due to inadequate stemming produces oversize in the face and perimeter zones of the blast.
The length of stemming is a function of many variables. Excessive stemming causes increased stiffness accompanied with excessive confinement, resulting in a range of problems. Rai3 reported excessive boulders in the blasted rock pile, especially from the collar zone, as a result of excessive stemming. Based on extensive studies, various researchers10,11,12 (and many others) have proposed the length of stemming column as a function of hole diameter, bench height or burden for optimum breakage in bench blasting.
Nevertheless, rule of thumb and the governing equations seem to work provided the integrity of the stemming column is maintained during the blasting sequence. To this end, plugging of the stemming column was tried along with changes to the existing firing pattern at a limestone quarry in the Philippines.
Objective
The main objective of the research programme was to achieve suitable fragmentation with good throw and minimum end break along the final wall so that the blasted rock could be easily loaded by front-end loaders. The loaders’ poor digging characteristics called for good fragmentation within the rock pile together with sufficient heave, to facilitate the loading operations.
The first author of this paper was requested to improve the productivity of the front-end loader by attempting suitable changes in the blast-design parameters to increase overall production and productivity at the quarry. The author visited the site to diagnose the problem areas and determine ways to resolve them. The following key observations formed the basis of the changes incorporated in the blasting practice:
Firing pattern influences the effective spacing to burden ratio at the time of detonation. Although V-type and diagonal firing patterns provide a similar effective spacing to burden ratio, the V-type firing pattern was deemed to be more suitable for the stated requirements because it increases the opportunity for in-flight collision between broken rock fragments. This particular characteristic of V-type firing was considered important to reduce fragment size and boulder occurrence within the blasted rock piles.
Furthermore, to obtain the maximum energy utilization for better heave of the blasted rock, blasthole plugging, as depicted in figure 3b, was achieved by the use of Vari-Stem plugs. The plugging was placed at the top of the explosive column without making any changes in the stemming length. The pre-existing diagonal pattern and modified V-type pattern are shown in figures 4 and 5.
Field description
To meet the stated objectives, full-scale blasts were conducted at the aforementioned limestone quarry in the Philippines, where annual production is in excess of 3 million tonnes. The quarry is worked in three sections – west, central and east. This study relates to the east section workings where the limestone beds, separated at 2–3m intervals, dip at an inclination of 30–40°. The geology of the deposit is quite difficult owing to frequent clay and shale intrusions. The compressive strength of the limestone is around 40MPa. The grade varies from 42.5% to 52.5%, the cut-off grade being 47%. The specific gravity of the limestone is 2.4. The east section comprises seven benches, each almost 9m in height.
The original loading operation was mainly performed by a 5m3 capacity front-end loader; the blasted rock being loaded on 35- and 50-tonne dumptrucks. As already mentioned, the loaders’ performance was unsatisfactory due to the presence of large boulders in the tight rock piles. Hence, a dozer and hydraulic breakers were deployed to facilitate loading operations. Furthermore, poor wall control and the appearance of end break was also apparent. Even with diagonal pattern firing, the heave (throw) was poor.
Research methodology
In order to fulfil the research objectives, many full-scale blasts were conducted at the quarry by varying crucial blast-design parameters on the limestone benches of the east section.
On critically evaluating the success of incorporating these changes on a 3.2m x 2.8m (spacing and burden) drill pattern, similar changes were attempted on incrementally expanded patterns up to 4.0m x 3.0m in order to positively exploit the stiffness parameter of the bench and, thereby, authenticate the validity of the changes. To quantitatively ascertain the improvements in the blast performance, the following blast evaluation parameters were closely monitored and recorded in the field on day-to-day basis:
Powder factor: The powder factor was precisely estimated by properly observing and recording the total number of trucks loaded during excavation of the entire rock pile. Proper scientific documentation of this data was extremely crucial. The total number of trucks was converted into tonnage using a truck factor, which in turn was calibrated by the conveyor weighing system. Oversize boulders that could not be handled by the front-end loader were separated at the bench and excluded from the tonnage computation. The total quantity of explosive actually loaded in the blast was registered in order to express the powder factor in terms of kg/tonne of limestone broken.
Boulder count: The total number of oversize boulders from the blast, which could not be loaded, were counted at the face. The fragment size accepted by the crusher was –75mm.
Loader cycle time: Several researchers13,14,15,16 have reported the relationship between the diggability of loading machines with respect to the degree of fragmentation in the rock pile. Hence, the cycle times of the front-end loaders were accurately recorded throughout the excavation so that realistic cycle-time data could be used as an index to blast performance.
Dozer performance: To facilitate the loading operations, dozers are often deployed in a blasting programme. However, excessive deployment of a dozer (expressed in terms of total dozing hours) is suggestive of poor blasting performance. Hence, the actual number of hours spent dozing the rock pile was also recorded to provide another reliable index to help evaluate the blast performance.
Throw and drop: As shown in figure 6, the throw, drop and lateral spread of the rock pile are crucial parameters for the success of the loading operation. Greater throw, drop and spread may be considered favourable for digging of the rock by front-end loader. During the fieldwork the throw and drop were measured immediately after each blast using tape measurements on the blasted rock pile.
End-break measurement: The presence of end break along the blast edges is extremely deleterious in terms of high-wall control and stability, and also in terms of subsequent blasts. For quantification purposes, the location and the linear extent of the end breaks were recorded by steel tape.
Result and discussions
A number of blasts were conducted in the quarry to fulfil the stated research objectives. Field observations and the blast performance results are tabulated in tables 1 and 2. All the blasts were drilled using a staggered drilling pattern with ANFO explosive and sensitized emulsion cartridge primers. The blasts were initiated by shocktube with delay sequencing. Table 1 gives comprehensive details of four experimental blasts: B1, B2, B3 and B4. Blast B1 was conducted on a diagonal firing pattern to generate the baseline data for the existing firing pattern and blast practices observed by the management. Key blast evaluation parameters, as discussed earlier, were registered for the baseline blast.
A perusal of these parameters for B1 reveals a powder factor of 0.27, large boulder count (40 nos), high loader cycle time (55s), high dozing time (17h), poor throw (4.5m) and drop (2.0m), and the emergence of end break (0.75m x 7.0m) along one of the edges of the blast. The large boulder count increased the front-end loader cycle time as a considerable amount of time was wasted dealing with these boulders. Total dozing hours were high due to poor throw and drop characteristics.
To address the problems observed in B1, changes were made to the firing pattern alone to initiate improvements. It was envisaged that, due to improved fragmentation by switching to V-type firing, the throw and drop might also improve. The results of B2 are indicative of significant improvements by way of a reduction in the boulder count (20 nos) and total dozing hours (13h), together with an increase in the spreading of the rock pile due to increased throw (6.0m) and a slightly increased drop value. These improvements clearly indicate improvement in the fragmentation within the rock pile. However, there was no reduction in the loader cycle time due to certain lapses in the planning of the dozer operation. Furthermore, the powder factor remained the same as in B1.
Stemming plug devices were deployed, without changing the length of stemming column, for blasts B3 and B4. The post-blast results clearly indicate the combined success of the V-type firing pattern in conjunction with the use of stemming plugs. Significant improvements were observed in terms of boulder count (5 nos), loader cycle time (50s), throw (8.75m), drop (3.50m) and spreading of the rock pile, as shown in fig. 7. It is important to note that although the powder factor (0.26) is higher for B4, the dozing hours (5h) and the throw (12.10m) for this blast provide favourable results with no end breaks. This may be attributable to the use of stemming plugs in the last two drilling rows in B4, compared to blast B3 where they were used only in the last row.
From the results of these changes, it may be interpreted that V-type firing provides better collision opportunities as a result of which fragmentation within the rock pile is improved and boulder count is reduced. Furthermore, the confinement of blasthole pressure for a longer period, due to the integrity of the stemming plugs, has led to better heaving of the blasted rock. The absence of end breaks in these blasts authenticates these interpretations.
Nevertheless, during the field observations with the previously mentioned modifications, it was observed (see fig. 8) that the fragment size was unnecessarily reduced (5–20mm). Hence, it was felt that the explosive energy could be better utilized by expanding the drill pattern area incrementally. Two blasts (B5 and B6) were conducted on a slightly increased area of 3.6m x 2.8m while keeping all other parameters the same as in B3 and B4. Looking at the powder factor (PF) results, as anticipated a marked reduction in the PF value (0.21) was witnessed for both blasts. The boulder count, loader cycle time and throw and drop values remained almost consistent, whereas dozing hours reduced substantially. As with blasts B3 and B4, blasts B5 and B6 also did not reveal any end breaks. The improvements can be seen in figs 9 and 10.
Encouraged by the success of the results obtained from B5 and B6, further expansion of the drill pattern area was attempted while keeping all other parameters the same as in B5 and B6. All the results from these two blasts (B7 and B8) were favourable and showed further improvements over blasts B5 and B6. Powder factor (0.19) showed significant improvement compared to the previous blasts. Other parameters were also improved.
Conclusions
A shift in firing pattern from diagonal to V-type has been effective in improving fragmentation, reducing the boulder count and also in improving the throw, drop and spreading characteristics of the rock pile. V-type firing in combination with stemming plugs has effectively retained the blasthole pressure for longer, which, in turn, seems to further increase the heaving characteristics of the blasted rock.
Due to better fragmentation and heave of the rock pile, the extensive use of a dozer to assist the front-end loader has been reduced by 88%, while the performance of the loader has also improved with a 16% reduction in cycle time. Explosive consumption has also been significantly reduced.
Under the given delay sequence (which could not be altered due to operational limitations), the changes in firing pattern, in conjunction with the use of stemming plugs, provided considerable control over the end breaks. Nevertheless, stemming plugs are costly and, hence, their usage calls for judicious planning based on categorical interpretation of the results.
References
By Dr Piyush Rai, reader in mining engineering; Bhanwar Singh Choudhary, senior research fellow, Department of Mining Engineering, Institute of Technology, Banaras Hindu University, India; and F.L. Imperial, president, Republic Aggregate Co. Inc., the Philippines
A firing pattern is like an electrical circuit, providing a pathway for a detonation wave in order that explosive charges in the blastholes can be initiated. In any blasting programme the foremost requirement is sequential generation of free face (with the blast progression). To this end, the firing pattern determines the movement and direction of rock by creating free face for subsequent blastholes/rows. Extensive work has been reported by various researchers1,2,3 on different types of firing pattern (row-to-row, diagonal, V-type and skewed V-type). The researchers suggest that each firing pattern has its own application. Proper use of pattern in relation to the blast requirements can provide optimal blast performance in terms of fragmentation, throw, wall control etc. This is largely attributed to the importance of firing burden in any blast. By changing the firing pattern, the firing burden, and thereby the ratio of spacing to burden, is also subject to change4,5.
Stemming the upper section of a blasthole with inert material confines and retains the gases produced by the explosion within the hole. Confinement and retention promote rock fracturing by transmitting a major proportion of shock as well as gas pressure through the broken rock mass prior to the release of the stemming.
Improper confinement results not only in wastage of energy and poor fragmentation, but also in environmental problems such as airblast, flyrock etc6,7. According to Brinkmann8, almost 50% of explosive energy is lost if premature venting is allowed to occur through the collar region of the blasthole. Floyd9 indicated that improper explosive confinement due to inadequate stemming produces oversize in the face and perimeter zones of the blast.
The length of stemming is a function of many variables. Excessive stemming causes increased stiffness accompanied with excessive confinement, resulting in a range of problems. Rai3 reported excessive boulders in the blasted rock pile, especially from the collar zone, as a result of excessive stemming. Based on extensive studies, various researchers10,11,12 (and many others) have proposed the length of stemming column as a function of hole diameter, bench height or burden for optimum breakage in bench blasting.
Nevertheless, rule of thumb and the governing equations seem to work provided the integrity of the stemming column is maintained during the blasting sequence. To this end, plugging of the stemming column was tried along with changes to the existing firing pattern at a limestone quarry in the Philippines.
Objective
The main objective of the research programme was to achieve suitable fragmentation with good throw and minimum end break along the final wall so that the blasted rock could be easily loaded by front-end loaders. The loaders’ poor digging characteristics called for good fragmentation within the rock pile together with sufficient heave, to facilitate the loading operations.
The first author of this paper was requested to improve the productivity of the front-end loader by attempting suitable changes in the blast-design parameters to increase overall production and productivity at the quarry. The author visited the site to diagnose the problem areas and determine ways to resolve them. The following key observations formed the basis of the changes incorporated in the blasting practice:
- Diagonal firing pattern did not provide the required fragmentation and desired throw.
- Large boulders occurred within the rock pile.
- Front-end loader had to be assisted by a dozer because of the coarse fragment size and tight rock pile, resulting in increased dozing costs.
- An irregular final wall profile after excavation of the blast.
Firing pattern influences the effective spacing to burden ratio at the time of detonation. Although V-type and diagonal firing patterns provide a similar effective spacing to burden ratio, the V-type firing pattern was deemed to be more suitable for the stated requirements because it increases the opportunity for in-flight collision between broken rock fragments. This particular characteristic of V-type firing was considered important to reduce fragment size and boulder occurrence within the blasted rock piles.
Furthermore, to obtain the maximum energy utilization for better heave of the blasted rock, blasthole plugging, as depicted in figure 3b, was achieved by the use of Vari-Stem plugs. The plugging was placed at the top of the explosive column without making any changes in the stemming length. The pre-existing diagonal pattern and modified V-type pattern are shown in figures 4 and 5.
Field description
To meet the stated objectives, full-scale blasts were conducted at the aforementioned limestone quarry in the Philippines, where annual production is in excess of 3 million tonnes. The quarry is worked in three sections – west, central and east. This study relates to the east section workings where the limestone beds, separated at 2–3m intervals, dip at an inclination of 30–40°. The geology of the deposit is quite difficult owing to frequent clay and shale intrusions. The compressive strength of the limestone is around 40MPa. The grade varies from 42.5% to 52.5%, the cut-off grade being 47%. The specific gravity of the limestone is 2.4. The east section comprises seven benches, each almost 9m in height.
The original loading operation was mainly performed by a 5m3 capacity front-end loader; the blasted rock being loaded on 35- and 50-tonne dumptrucks. As already mentioned, the loaders’ performance was unsatisfactory due to the presence of large boulders in the tight rock piles. Hence, a dozer and hydraulic breakers were deployed to facilitate loading operations. Furthermore, poor wall control and the appearance of end break was also apparent. Even with diagonal pattern firing, the heave (throw) was poor.
Research methodology
In order to fulfil the research objectives, many full-scale blasts were conducted at the quarry by varying crucial blast-design parameters on the limestone benches of the east section.
On critically evaluating the success of incorporating these changes on a 3.2m x 2.8m (spacing and burden) drill pattern, similar changes were attempted on incrementally expanded patterns up to 4.0m x 3.0m in order to positively exploit the stiffness parameter of the bench and, thereby, authenticate the validity of the changes. To quantitatively ascertain the improvements in the blast performance, the following blast evaluation parameters were closely monitored and recorded in the field on day-to-day basis:
Powder factor: The powder factor was precisely estimated by properly observing and recording the total number of trucks loaded during excavation of the entire rock pile. Proper scientific documentation of this data was extremely crucial. The total number of trucks was converted into tonnage using a truck factor, which in turn was calibrated by the conveyor weighing system. Oversize boulders that could not be handled by the front-end loader were separated at the bench and excluded from the tonnage computation. The total quantity of explosive actually loaded in the blast was registered in order to express the powder factor in terms of kg/tonne of limestone broken.
Boulder count: The total number of oversize boulders from the blast, which could not be loaded, were counted at the face. The fragment size accepted by the crusher was –75mm.
Loader cycle time: Several researchers13,14,15,16 have reported the relationship between the diggability of loading machines with respect to the degree of fragmentation in the rock pile. Hence, the cycle times of the front-end loaders were accurately recorded throughout the excavation so that realistic cycle-time data could be used as an index to blast performance.
Dozer performance: To facilitate the loading operations, dozers are often deployed in a blasting programme. However, excessive deployment of a dozer (expressed in terms of total dozing hours) is suggestive of poor blasting performance. Hence, the actual number of hours spent dozing the rock pile was also recorded to provide another reliable index to help evaluate the blast performance.
Throw and drop: As shown in figure 6, the throw, drop and lateral spread of the rock pile are crucial parameters for the success of the loading operation. Greater throw, drop and spread may be considered favourable for digging of the rock by front-end loader. During the fieldwork the throw and drop were measured immediately after each blast using tape measurements on the blasted rock pile.
End-break measurement: The presence of end break along the blast edges is extremely deleterious in terms of high-wall control and stability, and also in terms of subsequent blasts. For quantification purposes, the location and the linear extent of the end breaks were recorded by steel tape.
Result and discussions
A number of blasts were conducted in the quarry to fulfil the stated research objectives. Field observations and the blast performance results are tabulated in tables 1 and 2. All the blasts were drilled using a staggered drilling pattern with ANFO explosive and sensitized emulsion cartridge primers. The blasts were initiated by shocktube with delay sequencing. Table 1 gives comprehensive details of four experimental blasts: B1, B2, B3 and B4. Blast B1 was conducted on a diagonal firing pattern to generate the baseline data for the existing firing pattern and blast practices observed by the management. Key blast evaluation parameters, as discussed earlier, were registered for the baseline blast.
A perusal of these parameters for B1 reveals a powder factor of 0.27, large boulder count (40 nos), high loader cycle time (55s), high dozing time (17h), poor throw (4.5m) and drop (2.0m), and the emergence of end break (0.75m x 7.0m) along one of the edges of the blast. The large boulder count increased the front-end loader cycle time as a considerable amount of time was wasted dealing with these boulders. Total dozing hours were high due to poor throw and drop characteristics.
To address the problems observed in B1, changes were made to the firing pattern alone to initiate improvements. It was envisaged that, due to improved fragmentation by switching to V-type firing, the throw and drop might also improve. The results of B2 are indicative of significant improvements by way of a reduction in the boulder count (20 nos) and total dozing hours (13h), together with an increase in the spreading of the rock pile due to increased throw (6.0m) and a slightly increased drop value. These improvements clearly indicate improvement in the fragmentation within the rock pile. However, there was no reduction in the loader cycle time due to certain lapses in the planning of the dozer operation. Furthermore, the powder factor remained the same as in B1.
Stemming plug devices were deployed, without changing the length of stemming column, for blasts B3 and B4. The post-blast results clearly indicate the combined success of the V-type firing pattern in conjunction with the use of stemming plugs. Significant improvements were observed in terms of boulder count (5 nos), loader cycle time (50s), throw (8.75m), drop (3.50m) and spreading of the rock pile, as shown in fig. 7. It is important to note that although the powder factor (0.26) is higher for B4, the dozing hours (5h) and the throw (12.10m) for this blast provide favourable results with no end breaks. This may be attributable to the use of stemming plugs in the last two drilling rows in B4, compared to blast B3 where they were used only in the last row.
From the results of these changes, it may be interpreted that V-type firing provides better collision opportunities as a result of which fragmentation within the rock pile is improved and boulder count is reduced. Furthermore, the confinement of blasthole pressure for a longer period, due to the integrity of the stemming plugs, has led to better heaving of the blasted rock. The absence of end breaks in these blasts authenticates these interpretations.
Nevertheless, during the field observations with the previously mentioned modifications, it was observed (see fig. 8) that the fragment size was unnecessarily reduced (5–20mm). Hence, it was felt that the explosive energy could be better utilized by expanding the drill pattern area incrementally. Two blasts (B5 and B6) were conducted on a slightly increased area of 3.6m x 2.8m while keeping all other parameters the same as in B3 and B4. Looking at the powder factor (PF) results, as anticipated a marked reduction in the PF value (0.21) was witnessed for both blasts. The boulder count, loader cycle time and throw and drop values remained almost consistent, whereas dozing hours reduced substantially. As with blasts B3 and B4, blasts B5 and B6 also did not reveal any end breaks. The improvements can be seen in figs 9 and 10.
Encouraged by the success of the results obtained from B5 and B6, further expansion of the drill pattern area was attempted while keeping all other parameters the same as in B5 and B6. All the results from these two blasts (B7 and B8) were favourable and showed further improvements over blasts B5 and B6. Powder factor (0.19) showed significant improvement compared to the previous blasts. Other parameters were also improved.
Conclusions
A shift in firing pattern from diagonal to V-type has been effective in improving fragmentation, reducing the boulder count and also in improving the throw, drop and spreading characteristics of the rock pile. V-type firing in combination with stemming plugs has effectively retained the blasthole pressure for longer, which, in turn, seems to further increase the heaving characteristics of the blasted rock.
Due to better fragmentation and heave of the rock pile, the extensive use of a dozer to assist the front-end loader has been reduced by 88%, while the performance of the loader has also improved with a 16% reduction in cycle time. Explosive consumption has also been significantly reduced.
Under the given delay sequence (which could not be altered due to operational limitations), the changes in firing pattern, in conjunction with the use of stemming plugs, provided considerable control over the end breaks. Nevertheless, stemming plugs are costly and, hence, their usage calls for judicious planning based on categorical interpretation of the results.
References
- SMITH, N.S.: ‘Burden rock stiffness and its effects on fragmentation in bench blasting’, Ph.D. thesis, Univ. of Missouri, 1976, USA.
- HAGAN, T.N.: ‘The influence of controllable blast parameters on fragmentation and mining costs’, Procs. 1st Int. Symp. on Rock Fragmentation by Blasting, Lulea, Sweden, 1983, pp31–51.
- RAI, P.: ‘Evaluation of effect of some blast-design parameters on fragmentation in opencast mines’, Ph.D. thesis, Banaras Hindu University, Varanasi, 2002.
- RAI, P., and BAGHEL, S.S.: ‘Investigation of patterns on fragmentation in an Indian opencast limestone mine’, Quarry Management, 2004, vol. 31, no. 2, pp21–30.
- OLIVER, P.H.: ‘Changes to drill pattern and adequate inter-row delay time improve blasting performance’, Canadian Institute of Mining (CIM) Bulletin, vol. 96, May 2003, pp60–65.
- CHIAPETTA, R.F., and J.L. WYCISKALLA: ‘Bottom-hole and multiple power decks’, Quarry Management, 2004, vol.31, no. 2, pp21–30.
- MCLONGHLIN, M.: ‘Softly softly’, World Mining Equipment, vol. 28, no.1, Jan–Feb 2004, pp33–34.
- BRINKMANN, J.R.: ‘An experimental study of the effects of shock and gas penetration in blasting’, Procs. 3rd Int. Symp. On Rock Fragmentation by Blasting, Brisbane, Australia, 1990, pp55–66.
- FLOYD, J.L.: ‘Explosive energy relief – The key to controlling overbreak’, Procs. Int. Conf. Explo '99, 1999, Kalgoorlie, Western Australia, 7–11 Nov., pp147–153.
- ASH, R.L.: ‘The influence of geological discontinuities on rock blasting’, Ph.D. thesis, Univ. of Missouri, 1973, USA.
- RZHEVSKY, V.V.: ‘Opencast mining unit operations’, Mir Publishers, Moscow, 1985.
- KONYA, C.J.: ‘Problems with deck-loaded blastholes’, Engg. & Min Jour., July 1996, pp73–74.
- KANCHIBOTLA, SS.: ‘Optimum blasting? Is it minimum cost per broken rock or maximum value per broken rock?’, Procs. Explo-2001, Hunter Valley, New South Wales, pp35–40.
- RAI, P.: ‘Change that blast’, World Mining Equipment, vol. 27, no. 9, Nov 2003, pp43–45.
- MARTON, A., and R. CROOKES: ‘A case study in optimizing fragmentation’, The Aus. IMM Procs, No.1, 2000, pp35–43.
- SINGH, S.P., and T. YALCIN: ‘Effect of muck size distribution on scooping operations’, Jour. Int. Soc. of Expl. Engrs., 2002G, V.1, 2002, pp315–325.
