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--> 2 General Comments on the Draft Report of the DOE Working Group The March 1997 draft report of the DOE Working Group7 identifies and discusses the major sources that contribute to the generation of seismic signals associated with mining operations. These sources include events from blasting activities and planned and unplanned ground failures. The report provides documentation and discussion that suggest that some of these events may cause concerns for CTBT compliance and verification. As a result, it urges that the mining community be alerted and educated on the visibility of mining-related seismic signals and their ambiguous character. The DOE Working Group report contains a broad spectrum of useful data and analytical results on the nature of mining-related seismic signals. It is comprehensive in its review of the relevance of the CTBT to the mining industry from a technical perspective. Underground failures that may produce seismic signals are properly categorized in the report as (1) planned failures, which include controlled failures (e.g., planned pillar blasting and the initiation of block caving) and uncontrolled failures (e.g., strata caving in mining operations), and (2) unplanned failures, which include events such as pillar collapses, coal bumps, and rock bursts. The techniques presented in the DOE Working Group report for recording and analyzing seismic signals can be a valuable tool for assessing blasting performance in mines. Some of the signatures (e.g., seismic wave forms) of mining-related seismic signals can be similar to those of a nuclear test. Current instrumentation and the methods used to process and analyze seismic signals are not always capable of discriminating between a chemical and a nuclear blast. The recommendations of the DOE Working Group's report focus on modifications to blasting and underground mining practices that will reduce the amounts of energy placed in the ground (i.e., 7 The executive summary of the March 1997 draft report of the DOE Working Group is included as Appendix B.
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--> explosive charges used in rock blasting and energy from bursts or collapses) in an effort to reduce regional amplitudes of seismic signals. The DOE Working Group's recommendations place the burden on the mining industry to reduce the amount of energy going into seismic signals at the source rather than on the monitoring community to identify technical means for discriminating signals. An alternative approach, mentioned more briefly in their report, is to reduce the ambiguity of the nature of mining-related seismic signals. The recommendations proposed by the working group's report to reduce seismic levels prescribe changes to long-standing mining practices that have been refined to optimize equipment investments and operational costs, efficiency, and safety. The committee believes that the adoption of many of the working group's recommendations could result in a substantial increase in operational mining costs. Unfortunately, the DOE Working Group report makes no attempt to address these cost factors, without which the industry will not be readily receptive to the recommendations. The quantification of these costs is at best a difficult task and is best accomplished on a mine site-specific basis. Some generalized cost calculations associated with adopting some of the blasting recommendations are given in Table 1 and further discussed in Appendix A. In this example, drilling costs associated with changes in blasting practice may increase by a factor of two. Most of the blasting recommendations made in the DOE Working Group report are based on textbook blasting practices and are dated. Rock breakage is a costly unit operation that is given a high degree of technical attention at most TABLE 1 Calculation of the cost associated with reducing blasthole diameters and bench heights for two hypothetical cases. Design Factor Example 1 Example 2 (modified Example 1) Bench height 50 ft. 25 ft. Blasthole diameter (design) 10 in. 8-in. Hole spacing pattern 24 ft. 17 ft. Stem length 20 ft. 13 ft. Yardage of blast 1967 yd3 267 yd3 Explosive loading (1 lb/yd3 per blasthole 1022 lb. 262 lb. Number of blastholes to meet a weekly production rate of 300,000 yd3 281 1124 Drilled length per week 14,050 28,100 Weekly drilling cost (at $2 per foot) $28,000 $56,200 Annual drilling costa $1,461,200 $2,922,400 NOTE: Example 1 summarizes a typical blast design, whereas Example 2 is the modified blast design that limits the charge size used in Example 1 in response to recommendations by the DOE Working Group. This calculation is further discussed in Appendix A. a Costs depicted are a result of calculations for the hypothetical examples; actual drilling costs could vary by 25% or more.
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--> large mines. Some of the methodologies described in the working group's report have been used at many mines to monitor ground vibrations adjacent to structures, maximize blast design and efficiency, and minimize damage to open-pit walls. However, in the case of the DOE Working Group report's recommendation on slice mining, the technique is not a commonly known mining engineering method, is unreferenced, and is inadequately documented in the report. Parts of the working group's report are written in such a way as to imply that the mining industry has a limited understanding of the scientific, technical, environmental, and economic benefits of various blasting practices. The DOE Working Group report as written implies that “we are here to help you,” and that controls and assistance from outside the industry are needed to ensure that blasting is done appropriately. Despite the above criticisms, the DOE Working Group report could be highly useful if reframed as a resource document to inform the mining industry on the relevance of the CTBT to the industry, in terms of mining blasts and ground failures, and possible solutions to blasting problems pertinent to visible mine blasts. The report also identifies the need to consider similarities and differences of U.S. mining practices with those used internationally.
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