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Improving Fragmentation And Loading Rates Through Better Blasting With Varistem®

Table of Contents

The intent of the trial was to demonstrate the energy retention capabilities of the Varistem® blast stemming plugs through conducting a split blast on a production waste bench at a manganese mine in South Africa. The main results considered were to determine the difference in blast energy retention when using Varistem® with drill chippings as compared to using only drill chippings as stemming material (non-Varistem®). This was done through a visual analysis of the blast, a physical fragmentation analysis as well as the measurement of loading rates of the material. 


The overarching methodology that was used was as follows: 

  1. The waste bench was divided into two equal portions. 171mm (6.75”) Varistem® plugs were installed on one side to an average stemming height of 2.5m (8.2ft), with drill chippings used as stemming material.
  2. On the non-Varistem® side of the block, an average stemming height of 2.5m (8.2ft) was also maintained, using the same drill chippings for stemming material.
  3. The blast was initiated in the middle of the bench with hole detonation progressing to the east and west sides of the bench. This allowed for an accurate 50-50 comparison between the two sides of the bench.

The relevant blast parameters for the trial blast are shown in Table 1, with the bench layout and camera positioning shown in Figure 1, and further bench layouts from multiple angles in Figure 2. 

Table 1: Trial Blast Parameters

Blast Type:Waste Lower Lime/Calcrete
Geology:Uniform throughout the block
Holes on blast:1 343 holes
Burden and spacing:4.3m x 5.0m (14.1ft x 16.4ft)
Drill Depth:varied 15m (49.2ft)
Stemming Depth:2.5m (8.2ft)
Powder Factor:1.345
Stemming Material:Configurations of Drill Chippings; and Varistem® & Drill Chippings
Blast Timing:25ms between holes, 170ms between rows (Identical East & West Side)
Drill Pattern:Staggered 
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Figure 1: Blast Bench Layout and Camera Positioning

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Figure 2: Blast Bench Layout – Multiple Angles


The visuals from the South (Figure 3 and Figure 4) (in conjunction with the visuals from the North, not shown in this article) clearly indicate an increase in time to stemming movement as well as a reduction in the number, violence and velocity of blowouts. This shows that the Varistem® stemming plugs improved the energy retention on this blast, when considering the visual result in isolation. 

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Figure 3: Visual Analysis Outtakes – South

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Figure 4: Visual Analysis Outtake – South Thermal


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Figure 5: Ortho Muckpile View

Note the difference in the alignment of the muckpile peak (Figure 5), and power trough between the Varistem and Non-Varistem side. A uniform peak alignment indicates better energy distribution, while a wider power trough indicates improved energy retention. Figure 6 and Table 2 show the particle size distribution data from the fragmentation analysis that was conducted for the trial blast.

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Figure 6: Particle Size Distribution Curve – Varistem vs. non-Varistem

Table 2: Particle Size Distribution – Percentage Passing

Without Varistem®With Varistem®
% Passing  Size[cm]  Size[cm]
Topsize 84,7927,76

From the fragmentation results in Figure 6 and Table 2, it is evident that the fragmentation results on the Varistem® portion of the trial bench were far superior to that of the non-Varistem® portion of the bench: 

  • P50: Without Varistem® 44.6% larger than with Varistem®
  • P80: Without Varistem® 79.1% larger than with Varistem®
  • Topsize: Without Varistem® 205.4% larger than with Varistem®


Table 3: Load and Haul Trial Data

West – Varistem® & Drill ChippingsEast – Drill Chippings
Data points
Day Shift1721
Night Shift2021
Data Totals
Day Shift8 0369 345
Night Shift10 89810 586
Average BCM/hour
Day Shift472,71445,00
Night Shift544,90504,10
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Figure 7: Loading Rates – Varistem vs. Non-Varistem


In line with the overall intent of the trial, the following conclusions can be made: 

  • The visual data available from the two drones demonstrated the energy retention capabilities of the Varistem® stemming plugs. Time to stemming movement increased, and correspondingly the number of and violence and velocity of the blowouts reduced significantly. 
  • The thermal imagery indicated less heat escaping from the portion of the block that used Varistem® stemming plugs, as well as a significant decrease in surface shockwave activity. 
  • From the aerial shots the fragmentation appears to be much finer on the Varistem® side of the block. The fragmentation analysis showed that the fragmentation on the Varistem® with Drill Chippings side was significantly finer and more uniform than on the side with Drill Chippings only, with a significant decrease in topsize:
    • P50: Without Varistem® 44.6% larger than with Varistem®
    • P80: Without Varistem® 79.1% larger than with Varistem®
    • Topsize: Without Varistem® 205.4% larger than with Varistem®
  • In terms of loading rates, Varistem® with Drill Chippings loaded, on average, +7.8% (37.2 BCM/h) faster than Drill Chippings only.


  • Based on the results achieved, the use of Varistem® on waste material at this manganese mine in South Africa will result in:
    • A finer, more uniform fragmentation
    • A significant decrease in topsize
    • An increase in loading rates
  • The results presented in this report demonstrate sufficient merit to use Varistem® on waste blasts at the mine in order to realise the financial benefits associated with the improvement in fragmentation, reduction in topsize and increase in loading rates. 

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