Digital Detonators keep PA Coal Mine Operating

By Jay Elkin, Wampum Hardware Company

Douglas Bartley, DBA Consulting

The state of Pennsylvania was at one time one of the leading coal producing states in the east. However, legislation and industry trends over the last 10 years have adversely affected the amount of bituminous coal mined in Pennsylvania and the whole eastern United States. The application for and approval of a new mining permit is a very costly and arduous task. When a new mining operation is established it is crucial that nothing within the operators control causes the operation to stop producing. This paper discusses the action taken by a small mine in Pennsylvania when their blast induced vibrations rose to levels that typically would have resulted in a total mine shut down by the regulatory body governing such operations. The Rosebud Mining Co. in Gastown, PA is owned by Mr. Cliff Forest of Kittanning, PA and is located in Armstrong County, western PA. The Big Mac Leasing Co. has been contracted to perform the actual mining operations. The Big Mac Leasing mining method consists of block stripping with 2 D-11 Cat Dozers, and a Cat 992 supported with 3 Cat 777 rock trucks. The overburden on the coal reaches depths of 85 feet (26M). The intent of the permit was to strip mine the low-cover coal using conventional mining methods and then do a face-up for a deep mine operation entry. The permit application and proposed blasting activity were challenged by the local residents for many months prior to the eventual permit approval by the PA DEP (Pennsylvania Department of Environmental Protection) in 1999. The actual mining operations were begun in early 2000. Many site and environmental problems were encountered from the very start of excavation. The initial blasts were sinking shots with no relief resulting in very perceptible ground vibration levels. This exacerbated the already negative public opinion of the blasting operations, but the low dominant frequency seismic recordings were still below PA DEP regulations. The public disapproval and reaction to the mining operations were very publicized. As the mining approached the nearby town of Gastown, the vibration levels increased in magnitude. During the third cut of the mining cycle the mine once again received numerous complaints concerning the blasting activity. The mining permit was issued before the PA DEP regulations adopted the USBM RI8507 (United States Bureau of Mines, Report of Investigations 8507) Z-curve in July of 2001. The mandated vibration criteria stipulated in the mining permit was a flat

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1.0 inch per second (25.4mm/s) peak particle velocity. As the complaints increased in frequency, Big Mac Leasing started getting numerous field inspections by the DEP. In Pennsylvania, the DEP can suspend a mining permit because of what is termed, being a nuisance. After several heated public meetings and two low frequency seismic recordings right at the vibration limit, the DEP informed both Rosebud Mining and Big Mac Leasing that they had to mitigate the problem or they would suspend the mining permit.

The mining company then requested that the blasting contractor (Wampum Hardware Co.) develop with a new blast design that would resolve the vibration issues. A meeting between the mining operator, the blasting contractor and DBA Consulting (Blast and Vibration Consultants) concluded that there were 2 viable options that could reduce the ground vibrations.

1. Decking the blast holes to reduce the amount of explosives detonated per delay period (higher scaled distance).

2. The implementation of electronic detonators and a signature hole waveform technique to modify ground vibrations and improve blast performance.

The mining operator decided to initially attempt to resolve the problem by

decking the blast holes before the introduction of electronic detonators. The next scheduled blast consisted of 28 holes. The holes were loaded with 2 delays or decks per hole and a maximum amount of explosives of 261 pounds (119 kg) per deck, less than one-half the amount of explosives previously detonated per delay period. This blast was initiated using non-electric pyrotechnic blasting caps and resulted in a seismic reading of 1.04 inches per second (26.4 mm/s) PPV with dominant low frequencies. The shot duration was doubled to a length of 800 ms due to the decking design. This long duration blast vibration coupled with low dominant frequencies spawned numerous homeowner complaints to the PA DEP regional office. The PA DEP immediately responded by halting the blasting until an alternative plan could be established. This plan would maintain the 1.0 inch per second (25.4 mm/s) PPV or invoke the RI-8507 - Z curve variable vibration vs. frequency criteria that would reduce the acceptable vibration limits to 0.5 PPV (12.7 mm) at low frequencies. DBA Consulting, Wampum Hardware and the Rosebud Mining engineers met with the DEP to discuss the electronic detonators and the methodology of the signature hole technique. This technique required the initiation of a single signature hole loaded with the maximum amount of explosives we thought we might encounter. The DEP agreed, with the stipulation that if the signature hole vibrations exceeded the 1.0 ips (25.4 mm/s) PPV they would revoke the mining permit.

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The Signature Hole Technique The purpose of this signature hole study was to quantify the vibration

characteristics at the Woods and VanHorne residences adjacent to the Rosebud Coal Companys Permit in Gastown, PA in order to determine the optimum delay timing configuration to be utilized in their blasting operations. This optimum timing should yield reduced ground vibration levels, more acceptable vibration frequency characteristics and improved blast performance.

Blast induced ground vibration is an impact from the use of explosives that has historically been an extremely difficult problem to effectively resolve. There are many variables and site constants involved in the equation that when combined, result in the formation of a complex vibration waveform generated by the confined detonation of an explosive charge. The application of proper field controls during all steps of the drilling and blasting operation will help to minimize the adverse impacts of ground vibrations, providing a well designed blast plan has been engineered. This design would consider the proper blast hole diameter and pattern that would reflect the efficient utilization and distribution of the explosives energy loaded into the blast hole. It would also provide for the appropriate amount of time between adjacent holes in a blast to provide the explosive the optimum level of energy confinement. After the blast has been properly designed the parameters that have the greatest effect on the composition of the ground vibration waveform are: Geology between the blast site and the monitoring location Accurate timing between blast holes in a detonation sequence

Research developed by the USBM (United States Bureau of Mines), universities, and others over the last 15 years in the blasting industry, has concluded that a residential structures level of response to blast induced ground vibration is dependent on both the peak particle velocity and the frequency of the waveform. The frequency is the number of oscillations that the ground particles vibrate per second as a blast vibration wave passes by the structures location.

Above ground structures will resonate much like a tuning fork whenever they are exposed to a vibration wave containing adequate energy at the fundamental frequency of the structure. A structures resonant frequency is primarily dependent upon its mass, height and stiffness. The maximum response of a house to blast induced ground vibration occurs whenever the frequency of the ground vibration matches the natural resonant frequency of the house. Likewise, if there is little or no energy at the resonant frequency of the structure, the structural response to the vibration will be negligible.

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Further studies have also shown that there are direct relationships between the firing times of blast holes in a detonation sequence and the frequency composition of the ground vibration recorded at a particular structure in question. These studies have also observed that a total blast sequence is simply defined as a series of single hole detonations that are separated by a given amount of time (t). It is the relationship between this t and the geology of the site that has the most effect on the amplitude and frequency composition of the ground vibration wave. The geology is generally the constant in the equation but it will change as the blasting operations move throughout the mine or quarry.

This relationship between timing and geology has led to the development of several sophisticated computer programs to predict and modify ground vibrations. These programs will process the ground vibration signal recorded through the detonation of a single hole blast at a given production blast location. The computer then performs thousands of mathematical iterations that generate a synthesized complex waveform determining waveform amplitude and frequency composition for any given t between adjacent holes in a row and t between consecutive rows in a blast.

The major limitation of these software systems since their development has been the inherent inaccuracy of the pyrotechnic delay elements currently available in todays explosives market. The application of these computer prediction and control programs, often will recommend optimum delay timing intervals that are not available. Even if the computer times are achievable through combinations of available surface and in hole detonators, the inherent scatter in pyrotechnic detonators will cause the blast sequence to fire at times other than the designed firing time. These variances from the nominal firing times can potentially result in magnifying the impact rather than mitigating it. The introduction of a high accuracy electronic detonator into the commercial explosives market has had many positive effects in the area of predicting and controlling blast induced ground vibrations. It has been the experience of the author that without the implementation of electronic detonators the above software techniques are very ineffective.

Electronic detonators also offer the flexibility in blast timing design that

has never before been achievable. All commercial detonators to date have been manufactured with pre-set firing times that have evolved around vibration criteria and statistics that have since been questioned as to their relevance, ie. the 8 millisecond criteria.

Prior to the introduction of user programmable electronic detonators, an optimized site specific timing sequence that would provide maximized benefits in terms of vibration control, fragmentation, muck pile configuration and heave were

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unobtainable. The firing times were chosen from the limited selections available to the consumers. The introduction of the high accuracy detonators will provide the opportunity to design blasts based upon the desired results required by the user.

The detonator used in conjunction with this study is the Daveytronic

Programmable Electronic Blasting System. This detonator is manufactured by the Davey Bickford Company in France. The Daveytronic Blasting System pictured below, is capable of firing up to 1,500 detonators in a single blast with firing times from 1 ms to 4,000 ms with a firing accuracy of 0.1 ms.

The composition of the detonator consists of a ASIC (application specific integrated circuit), one logic capacitor, one firing capacitor and the high explosive charge within a standard sized shell compatible with any pre-cast booster.

D A V E Y T R O N I C Cross Section of detonator.

1. Circuit board IED assembly.

2. Duplex detonator wire.

3. Crimped plug.

4. Logic capacitor.

5. ASIC processor.

6. Firing capacitor.

7. Fuse head.

8. Primary charge.

9. Base charge.

The Daveytronic

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Implementation of the Signature Hole Technique In order to obtain meaningful vibration signature waveforms for use in the

vibration prediction program a single hole test blast was detonated on November 6, 2001. The blast geometry and loading details of the test hole are as follows:

Location Of Seis

Distance From Seis

FT / M

Depth

FT / M

Diameter

IN / mm

Burden

FT / M

Explosive Weight

Lbs. / KG Woods 720 / 219 41 / 12.5 6.75 / 172 15 / 4.6 521 / 236

VanHorne 830 / 253 41 / 12.5 6.75 / 171 15 / 4.6 521 / 236

The ground vibrations from the blasting operations were recorded at the Woods and VanHorne residences located on Route 210 in Gastown. The Woods residence is a two-story frame structure located north of the test hole. The VanHorne residence is a one-story frame structure located west of the test hole.

Figure 2 - VanHorne residence Figure 1 - Woods residence

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Signature Hole

The following waveform represents the single hole vibration characteristics

recorded at the Woods residence on November 6, 2001. The plot on the right depicts the FFT analysis of the single hole test blast. Note the high levels of low frequency dominant energy.

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The seismographs used in this study were the Mini-Seis seismographs manufactured by Larcor, Inc. of Quinlan, TX. These units are micro-processor

controlled digital seismographs that were configured to record vibration data at the sampling rate of 1024 samples per second per channel. The seismographs are self triggering units that were armed to trigger at a vibration threshold of 0.05 inches per second peak particle velocity. The seismographs are designed and calibrated to record vibration levels within a frequency range of 2 - 200 hertz from 0 - 5.0 inches per second (127mm) peak particle velocity.

Figure 3 - Digital seismograph

The analysis of the production blast data indicates that the horizontal

components of the waveform contain significant energy between 10 and 14 hertz. It is the horizontal components of the vibration wave that have the most effect on above ground structures in terms of structural response. Typical residential structures, by their design, are more susceptible to induced resonant mid-wall bending and corner shear racking by the horizontal components of a blast induced vibration. The vertical components have more effects on the ceiling and floor shear responses.

Each of the test hole blasts were processed individually in order to provide a timing configuration unique to the particular bench or mining level to be blasted. The analysis procedures were also conducted to provide timing information for a single and a double row of blast holes. The table below indicates the recommended hole-to-hole and row-to-row timing.

Hole (ms) Row (ms)

22 89

The delay intervals of 22ms between adjacent holes in a row and 89ms between rows results in 2 holes being detonated within the 8 millisecond criteria. The DEP inspectors had a very hard time accepting that this new design would effectively double the amount of explosives detonated per 8 ms delay. Approval was eventually given by the DEP to implement the new blast design with the electronic detonators with the stipulation that if the recorded PPV exceeded the 1.0 (25.4mm) PPV, they were going to revoke the mining permit.

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Electronic Production Blasting The signature hole study report stated that the best scenario would be to

blast 2 rows of up to 10 holes per row with each blast. The first two electronic

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detonator blasts were fired on November 13, 2001. The 16 hole blast consisted of 2 rows of 8 holes with 832 pounds (378 KG) of explosives firing within 8 ms. The preceding vibration recordings are from the November 13, 2001 blast. Note the lack of PV data points below 10 hertz and the reduced peak particle velocity at both the recording locations. The PPV of this blast was 0.35 inches per second (8.89 mm/s), representing 35% of the PPV of the decked pyrotechnic blast.

The blast induced ground vibrations that were recorded were dramatically

lower than the decked blast with pyrotechnic detonators. The blast duration was also reduced by 557 ms from 800 ms to 243 ms. It is the duration of a vibration that can cause an above ground structure to amplify the vibration through resonance. A shorter duration blast will always be perceived as a better blast by adjacent homeowners because of this.

The second electronic detonator blast was fired on December 5, 2001. We

fired 30 holes with a maximum of 1210 lbs (550 KG) per delay. The Scaled Distance worked out to 15.8. Our seismic recordings indicated that we were on the right track. The following seismic recordings were from the December 5th blast at the Gastown Permit.

The following chart summarizes the blast information and vibration data for the initial electronic blasting conducted at the mine. The electronic timing designs consistently resulted in dominant frequencies above 20 hertz providing less restrictive (RI 8507) vibration limits.

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Gastown Mine SMP 03000103

Armstrong County / Plum Creek Township

Big Mac Leasing Co. / Rosebud Mining Co.

Date Seis. No.

Distance FT / M

Ch. Wght.Lbs / KG SD

PPV Ips / mms Hz Location

12/5/01 1478 550 / 168 1160 / 527 16.1 0.72 / 18.3 36.4 WOOD

12/13/01 1477 700 / 213 772 / 351 25.2 0.46 / 11.7 15.0 VANHORNE

12/14/01 1477 630 / 192 386 / 176 33.7 0.41 / 10.4 12.0 VANHORNE

12/14/02 1477 700 / 213 708 / 322 26.3 0.55 / 14 13.0 VANHORNE

12/17/01 1477 700 / 213 704 / 320 26.3 0.40 / 10.2 13.2 VANHORNE

12/18/01 1477 630 / 192 386 / 176 32.1 0.39 / 9.9 13.4 VANHORNE

1/4/02 1478 600 / 183 466 / 212 27.7 0.39 / 9.9 32.0 WOOD

1/4/02 1478 520 / 158 370 / 168 27.0 0.34 / 8.6 30.1 WOOD

1/7/02 1478 580 / 177 402 / 183 28.0 0.46 / 11.7 28.8 WOOD

1/16/02 1478 530 / 162 482 / 219 24.1 0.49 / 12.4 24.3 WOOD

1/17/02 1478 510 / 155 498 / 226 22.9 0.65 / 16.5 28.4 WOOD

1/18/02 1478 510 / 155 530 / 241 22.2 1.00 / 25.4 26.9 WOOD

1/22/02 1478 457 / 139 457 / 208 22.7 0.95 / 24.1 26.9 WOOD

1/23/02 1478 375 / 114 750 / 341 13.7 0.71 / 18.0 32.0 WOOD

1/24/02 1478 425 / 130 375 / 171 21.9 0.87 / 22.1 34.1 WOOD

1/29/02 1478 435 / 133 400 / 182 21.7 0.68 / 17.3 36.5 WOOD

1/30/02 1478 430 / 131 425 / 193 20.8 0.67 / 17.0 32.0 WOOD

1/31/02 1478 430 / 131 425 / 193 20.8 0.60 / 15.2 34.1 WOOD

2/1/02 1478 435 / 133 425 / 193 21.1 0.58 / 14.7 36.5 WOOD

2/5/02 1478 437 /131 450 / 205 20.6 0.64 / 16.3 18.2 WOOD

2/6/02 1478 440 / 134 480 / 219 20.1 0.42 / 10.7 34.1 WOOD

2/7/02 1478 500 / 152 492 / 224 22.5 0.42 / 10.7 21.3 WOOD

2/7/02 1478 443 / 135 510 / 232 19.6 0.42 / 10.7 21.0 WOOD 2/11/02 1478 535 / 163 640 / 291 21.1 0.75 / 19.1 18.0 WOOD

2/12/02 1478 545 / 166 656 / 298 21.2 0.57 / 14.5 22.2 WOOD

2/19/02 1478 690 / 210 516 / 235 30.3 0.39 / 9.9 28.4 WOOD

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As the mining progressed the filter or geology between the blast location and the recording locations changed resulting the vibration signals being conditioned differently. The characteristics of the vibration recordings indicated that a second signature hole study should be conducted to again determine the optimum timing sequence to mitigate the negative vibration impacts. This second study was conducted on January 3, 2002.

The blast geometry and loading details of the test hole was as follows:

Location Of Hole

Distance From Seis

FT / M

Depth FT / M

Diameter IN / mm

Burden FT / M

Explosive Weight

Lbs. / KG East Side 550 / 168 30 / 9 6.75 / 172 15 / 4.5 342 / 156

The vibration recordings were again obtained from the Woods and the

VanHorne residence for use in this study. Each of the test hole blast recordings were processed individually with higher weighting placed on the VanHorne data recording due to its closer proximity to the blast area. The table below indicates the recommended hole-to-hole and row-to-row timing.

Hole (ms) Row (ms) 33 76

The above timing sequence was implemented on January 18, 2002. The

seismic recordings below depict the blast induced ground vibrations generated by the production blast. Again, the timing configuration of the blast resulted in 2 holes being fired within the 8 millisecond criteria effectively doubling the reported maximum pounds detonated per delay period.

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The preceding seismic analysis again indicates that the technique has

effectively produced seismic signals without high levels of energy in the low frequency band. In fact, the following blasts resulted in peak particle velocity levels at higher frequencies that provided maximum allowable PPV limits greater that the flat 1.0 inch per second (25.4 mm/s) in the original mining permit.

PA DEP Site Regression Study

The implementation and success of this technique at the Rosebud Mine has

been and is still currently being closely monitored by the PA DEP. During the months of blasting using the electronic detonators at the mine, the DEP has conducted their own seismic monitoring and analysis study. This study was to make sure the operator did not exceed the regulatory limit and to gain a better understanding of electronic detonators and their effect on blast vibrations. The vibration study was conducted by Mr. William Shush, a blasting inspector from the Greensburg, Pennsylvania office of the PA DEP.

During the months following the initial implementation of the Daveytronic

Programmable electronic detonators the DEP has monitored the ground vibrations in several locations adjacent to the mine site. They also conducted a linear regression analysis study at the Rosebud Mining Permit.

Seismograph Attenuation Line

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The study first correlated the data gathered prior to the implementation of

electronic detonators to determine the regression characteristics of the pyrotechnic detonators. Then an array of 9 seismographs were installed to monitor blasting operations for a total of 5 electronic blasts from April 4, 2002 to May 23, 2002. Using this electronic detonator data from the attenuation line of seismographs and the units installed at residential structures adjacent to the mine, the DEP determined the site regression characteristics of the electronic detonators. The table containing the blasting data and vibration data collected by the PA DEP to determine the site characteristics of the Gastown Site using the Electronic Detonators is in the appendix of this report.

The following chart exhibits the comparison between the actual electronic

detonator PPV recordings and the predicted pyrotechnic PPVs using the regression attenuation formula of:

Predicted: PPV pyrotechnic = 145 (SD) 1.4

Electronic Cap Study Gastown Mine Predicted Pyrotechnic PPV and Actual Electronic PPV

Power Regression Curve

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60

Scaled Distance

PPV PPV Actual

Predicted WC Pyro.

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The derived attenuation formula of the electronic detonators with an R2 goodness of fit, of 89% is :

Actual: PPV electronic = 74 (SD) 1.49

The comparison of the prediction formulas demonstrates both the better fit of data when using precision electronic data and the lower Site Constant resulting in a lower predicted PPV for the same blast when using electronic detonators. This goodness of fit has been a consistent trait of the electronic detonators in practically every application where vibrations were closely monitored. It provides a higher level confidence to a blast design as to the expected magnitude of the vibration impacts.

Conclusion

The introduction of electronic detonators at the Rosebud Coal Mine in

Gastown, PA has enabled the mine to stay in business. The public outcry against the blasting operations placed the mine under high scrutiny by the regulatory bodies that issue the permits and monitor the compliance of the mining operations. The PA DEP was poised and ready to revoke the mining permit at the Gastown Mine due to the impacts of the blasting operations.

The implementation of electronic detonators in conjunction with State of

the Art analytical and design techniques has successfully demonstrated the usefulness of programmable electronic detonators. It is the opinion of the authors that this scenario can and will be repeated with the same level of success in our industry as we embrace the technology and benefits the electronic detonator has to offer.

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Appendix

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Gastown Mine SMP 03000103 Armstrong County / Plum Creek Township Big Mac Leasing Co. / Rosebud Mining Co. Date Seis. No. Distance Ch. Wt. C^2 SD PPV L T V FL FT FV AOP Location

Shot # 1 4/4/01 2747 1660 756 27.5 60.4 0.12 0.09 0.12 0.05 31.2 26.3 19.2 117 S-1-3 4/4/01 2746 1450 756 27.5 52.7 0.19 0.19 0.13 0.1 23.8 17.2 55.5 118 S-1-2 4/4/01 4900 885 756 27.5 32.2 0.29 0.29 0.19 0.28 29.4 22.7 21.7 129 S-1-1

Shot #2 4/26/01 4904 2215 378 19.4 113.9 0.07 0.05 0.07 0.03 6 12.8 21.7 109 S-2-11 4/26/01 4108 1833 378 19.4 94.3 0.17 0.11 0.17 0.05 14.3 18.5 9.4 S-2-10 4/26/01 4899 1799 378 19.4 92.5 0.07 0.07 0.07 0.03 17.2 6.3 15.6 S-2-9 4/26/01 2746 1654 378 19.4 85.1 0.18 0.09 0.18 0.05 33.3 25 27.7 114 S-2-8 4/26/01 2747 1380 378 19.4 71.0 0.13 0.13 0.09 0.06 6.7 10 45.4 S-2-7 4/26/01 4900 1377 378 19.4 70.8 0.11 0.1 0.11 0.09 20 19.2 45.5 116 S-2-6 4/26/01 4105 1350 378 19.4 69.4 0.15 0.15 0.12 0.07 17.2 18.5 45.5 S-2-5 4/26/01 4085 1060 378 19.4 54.5 0.23 0.23 0.19 0.17 33.3 21.7 55.6 114 S-2-4 4/26/01 4903 925 378 19.4 47.6 0.19 0.11 0.1 0.1 11.4 23.8 21.7 10 S-2-3 4/26/01 4106 400 378 19.4 20.6 0.87 0.71 0.87 0.43 15.2 21.7 41.7 127 S-2-2 4/26/01 4107 265 378 19.4 13.6 1.28 1.28 0.97 0.85 13.9 19.2 45.5 S-2-1

Shot # 3 5/22/01 2644 147 612 24.7 5.9 3.92 3.16 3.92 3.52 9.4 10.2 18.5 134 S-3-8 5/22/01 4085 1861 612 24.7 75.2 0.15 0.06 0.15 0.06 10.2 12.8 16.7 114 S-3-7 5/22/01 4105 1368 612 24.7 55.3 0.13 0.13 0.12 0.08 11.9 14.7 8.2 117 S-3-6 5/22/01 4106 1141 612 24.7 46.1 0.19 0.18 0.19 0.11 8.8 10.4 16.7 117 S-3-5 5/22/01 4899 648 612 24.7 26.2 0.73 0.73 0.67 0.39 12.5 13.5 25 123 S-3-4 5/22/01 4900 807 612 24.7 32.6 0.51 0.45 0.51 0.24 20.8 19.2 29.4 123 S-3-3 5/22/01 4903 983 612 24.7 39.7 0.50 0.32 0.5 0.18 10.9 10.4 15.2 100 S-3-2 5/22/01 4904 1756 612 24.7 71.0 0.24 0.08 0.24 0.05 20.8 10.9 4.5 117 S-3-1

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Shot # 4 5/22/01 2644 526 486 22.0 23.9 1.48 0.7 1.48 1.48 15.6 19.2 29.4 133 S-4-9 5/22/01 4085 1580 486 22.0 71.7 0.15 0.15 0.09 0.07 9.6 11.1 25 117 S-4-8 5/22/01 4105 1176 486 22.0 53.3 0.14 0.14 0.12 0.14 26.3 19.2 27.8 121 S-4-7 5/22/01 4106 913 486 22.0 41.4 0.41 0.41 0.24 0.18 27.8 13.2 22.7 123 S-4-6 5/22/01 4107 316 486 22.0 14.3 1.52 1.52 0.98 1.18 11.4 20.8 41.7 133 S-4-5 5/22/01 4899 790 486 22.0 35.8 0.80 0.8 0.52 0.44 17.9 21.7 31.3 126 S-4-4 5/22/01 4900 913 486 22.0 41.4 0.55 0.55 0.43 0.28 50 35.7 62.5 124 S-4-3 5/22/01 4903 1106 486 22.0 50.2 0.41 0.27 0.41 0.15 20 10.9 23.8 100 S-4-2 5/22/01 4904 1861 486 22.0 84.4 0.20 0.19 0.2 0.08 11.9 33.3 31.3 119 S-4-1

Shot # 5 5/23/01 4085 1525 612 24.7 61.6 0.14 0.09 0.14 0.04 5.3 13.9 5.5 116 S-5-7 5/23/01 2747 1453 612 24.7 58.7 0.29 0.16 0.29 0.07 6.5 10.6 11.3 118 S-5-6 5/23/01 4108 1330 612 24.7 53.8 0.18 0.11 0.1 0.18 35.7 62.5 167 110 S-5-5 5/23/01 4106 1120 612 24.7 45.3 0.21 0.11 0.09 0.21 167 83.3 167 109 S-5-4 5/23/01 4107 924 612 24.7 37.4 0.29 0.17 0.09 0.29 20.8 100 167 109 S-5-3 5/23/01 4900 900 612 24.7 36.4 0.52 0.37 0.52 0.28 13.9 11.9 20 123 S-5-2 5/23/01 4899 730 612 24.7 29.5 0.77 0.45 0.77 0.27 10.9 13.5 23.8 124 S-5-1

Implementation of the Signature Hole TechniqueExplosive

Hole (ms)Row (ms)22

89Gastown Mine SMP 03000103Lbs / KGSD

Explosive

Hole (ms)

Row (ms)33

76