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Rock excavated with (A) excessive blasting and (B) controlled blasting

Background

Falls of ground are a significant hazard for miners and a leading cause of fatalities. MSHA data from 1998-2002 indicate that 61 of 141 (43%) of the underground fatalities during that period were caused by fall of ground. Where drill-and-blast techniques are used to excavate rock, poor blasting design or practices can exacerbate support problems, increasing worker exposure to hazards. Heavily damaged rock surrounding excavations requires more scaling, more support, and hence more rock bolt drilling than less-damaged rock. Substantial damage to the rock mass and poor blasting practices can also contribute to rock falls even after support systems have been put in place and may contribute to additional health and safety hazards involving:

1. Secondary breaking of oversize rock, manually or by drilling and blasting,
2. Undetonated explosives in muck piles, blast hang-ups, or an increase in noxious fumes,
3. Overbreak resulting in irregular opening surfaces that negatively impact ventilation and create uneven roadways, or
4. Ground shocks of sufficient intensity to damage mine equipment and infrastructure.

A number of cases of successful controlled blasting trials at mining operations have been published. However, even though techniques to minimize blasting damage exist, they are not systematically being applied throughout the U.S. mining industry. The goal of the proposed research is to provide the design criteria for optimizing blast designs and to demonstrate that better perimeter control and support system designs for excavations that incorporate advanced fragmentation techniques can significantly decrease the number of accidents associated with ground fall injuries from blast-damaged rock. Major project tasks include:

1. Evaluation of both laboratory and field of blast damage models to validate those that realistically predict the relationship between charge density, explosive energy, distance, rock material properties, rock structure, and rock damage in a spectrum of rock types,
2. Building a database of dynamic rock properties and developing laboratory and field analytical methods to assist industry in predicting the extent of blast damage,
3. Developing a fragmentation/support index that uses geological and geotechnical assessments to estimate rock blastability, rock mass quality, and support requirements,
4. Assessing current industry blasting practices at cooperating mines to quantify results of varying blast designs,
5. Conducting field demonstrations of optimized rock extraction that include improved support application, and
6. Conducting a thorough cost analysis to evaluate and compare costs of industry’s current practices to the NIOSH-optimized rock extraction systems.

Results of the research will be communicated to the mining community and the effectiveness of this research in changing blasting practices and reducing injury rates due to ground-control-related accidents will be assessed.

Potential Outcome

This research will develop new, scientifically valid, yet practical methods to provide recommendations on blast design, blast damage assessment, safer scaling, rehabilitation, and ground support installation. The efficiencies gained by integrating the design of the excavation/support process will result in a reduction of fatalities and traumatic injuries when rock is blasted in underground mines. The results of this research will be available to industry by 2010.

Outputs