Book name: Construction Methods and Management Stephens W. Nunnally Eighth Edition

Question: You measure a seismic velocity of9000 ft/s (2743 m/s)in limestone.Would you expect this rock to be rippableby a D9H tractor equipped with a ripper (Figure 17)?Ifso,would you recommend using a single or tandemripper in this situation? Why?

Question 2: Estimate the hourly production and unit cost ofrockexcavation by drilling and blasting.The rock is a lime-stone having a seismic velocity of6000 ft/s (1830 m/s).Trial blasting indicates that 31⁄2-in.(8.9-cm) holesdrilled in an 8-ft (2.44-m) rectangular pattern willprovide the desired fracturing.A hole depth of20 ft(6.1m) yields an effective depth of18 ft (5.5 m).Theaverage drilling rate is estimated to be 70 ft/h(21.4m/h).Apowder factor of1 lb/BCY (0.59 kg/BCM)ofANFO will be used.

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

Question 3: A tractor-mounted ripper will be used for excavating alimestone having a seismic velocity of6000 ft/s (1830m/s).Field tests indicate that the ripper can obtain satis-factory rock fracturing to a depth of2 ft (0.61 m) withone pass ofa single ripper shank at 3-ft (0.91-m) inter-vals.Average ripping speed for each 400-ft (122-m) passis 1.5 mph (2.4 km/h).Maneuver and turn time at theend ofeach pass averages 0.3 min.Job efficiency isestimated at 0.70.Machine cost including the operatoris$130/h.Estimate the hourly production and unit costofexcavation.