Estimate the hourly production and unit cost of rock excavation by drilling and blasting. The rock is a limestone having a seismic velocity of 6000 ft/s (1830 m/s).

Trial blasting indicates that 31⁄2-in. (8.9-cm) holes drilled in an 8-ft (2.44-m) rectangular pattern will provide the desired fracturing. A hole depth of 20 ft

(6.1 m) yields an effective depth of 18 ft (5.5 m).

The average drilling rate is estimated to be 70 ft/h

(21.4 m/h).A powder factor of 1 lb/BCY (0.59 kg/BCM)

of ANFO will be used.

Transcribed Image Text:

Cost Information: Labor: Drilling crew $40.00/h Blasting crew $42.00/h Drilling equipment $70.00/h Material: ANFO $0.40/lb ($0.88/kg) Primer, caps, & stemming $4.00/hole