Tunnels, Shaft and Development Headings Blast Design
TUNNELS, SHAFT AND DEVELOPMENT HEADINGS BLAST DESIGN INTRODUCTION Tunnels, shafts, and raises are developed for a variety of purposes. In mines development headings provide; mine access for men and materials, ore and waste hoisting, and ventilation paths. Shafts are also used in civil construction projects. In hydroelectric projects, shafts and tunnels are used to build spillways around dams, and penstocks for water feed to underground power plants. Large tunnels are also used to build underground rail and roadways. Design principles for shaft, tunnel, and raise rounds are reviewed and demonstrated in this section. Hanging Lake Tunnels on Interstate 70, Glenwood Springs, CO REVEY Associates, Inc. 2005 Page 1 Underground Blasting Technology ______________________________________________________________ DEFINING REQUIREMENTS AND CONDITIONS In an ideal situation, designers would have unlimited choices regarding explosives selection, and drilling equipment. However in most situations, blast designers do not have complete control over all of the variables affecting blast design. Round dimensions are usually pre-set, and designers must often accept the limitations that come with using existing drilling equipment drilling equipment. Despite some limitations, many other design elements can be adjusted to improve round design. Drill patterns and explosive loads can be modified, and within drilling equipment limits, hole-size can be changed. Following, is a list of typical considerations that designers should define when they develop new, or attempt improvement to existing, heading rounds. HEADING ROUND DESIGN CONSIDERATIONS 1. Heading production goals; advance rates, and schedule. 2. Ground conditions; rock strength and structure. 3. Shaft or tunnel excavation dimensions. 4. Overbreak limitations, and perimeter loading specifications. 5. Vibration and airblast limits.
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