A tractormounted ripper will be used for excavating a limest

A tractor-mounted ripper will be used for excavating a limestone having a seismic velocity of 6000 ft/s. field tests indicate that the ripper can obtain satisfactory rock fracturing to a depth of 2 ft with one pass of a single ripper shank at 3 ft intervals. Average ripper speed for each 400 ft pass is 1.5 mph. Maneuver and turn time at the end of each pass average 3.0 min. Job efficiency is estimated at 0.70. Machine cost including the operator is $130/h. Estimate the hourly production and unit cost of excavation

Solution

(a) Hourly production:

It can be calculated by the formula: Production(BCY/n) = (2.22*D*W*L*E)/T

Here, D is average penetration depth=2 ft.

W is average with loosened = 3 ft.

L is length of pass = 400 ft.

E is job efficiency = 0.70

T is time for one ripper pass including turn = (400ft./1.5mph) + 3.0 min

convert mph to ft./min 1.5mph = 1.5*88 ft./min

T= 3.03 min + 3.0 min = 6.03 min

now put all values in main equation of production, we get

Prodduction = 2.22*2*3*400*0.70/6.03 BCY/h

= 618.50 BCY/h

(b) unit cost of excavation

total cost = $130/h

unit cost = ($130/h)/(618.50 BCY/h)

= $ 0.21/BCY

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