Question

Please solve problem 1 and show formulas used

Homework 6- Chapter 9 Problem 1: A crawler hoe having a 2 -cy bucket and whose cost per hour, including the wages to an operator, is $109 will excavate and load haul units under each of the stated conditions. The maximum digging depth of the machine is 22 ft. Determine the cost per bank cubic yard for each condition. (Condition 1: 315 bey/hr, S0.346/bcy; condition 2: 289 bey/hr, S0.377/bcy; condition 3: 99 bey/hr, $1.101/bcy) Condition (2) (1) Moist loam, Material Sand and gravel 12 80 earth Depth of excavation (t) Angle of swing (degrees) 15 Percent swell 14 Efficiency factor (min per hr) 45 50 60

Tables for reference:

Answer 1

Solution as follows:

Formula for productivity of an excavator:

3600 x Q XFXE Productivity P (CY /hour) = t x 60 x (1 + 5)

In above formula,

Q = Bucket Capacity (CY)

F = Fill Factor

E = Efficiency (min/hr.)

t= cycle time (sec)

S = Free Swell index

1. Determination of productivity and cost for moist loam, earth

Maximum digging depth for hoe =22 ft

Depth of excavation = 15 ft

% Depth = 15/22 = 68%

Angle of swing = 60^o

Hence the hoe is working above average conditions (As per conditions stated in table 9.5)

Q = 2 cy

F = 105% =1.05 (Average value for moist loam from table 9.4)

E = 50 min per hour

t = 19 sec (due to digging depth is 68% of maximum digging depth, additional 2sec per cycle assumed than given in table 5)

S = 0

Hence,

3600 x 2 x 1.05 x 50 Productivity P =- = 331.5789 cy/hour P = 19 x 60 X (1+0)

The above productivity falls under condition 1. Hence haul cost shall be $0.346 per bcy

Cost of hoe per hour = $109

$109 Cost of excavation per cy = 331 5789 = $0.3287per cy

Total Cost for sandy loam, earth = Cost of excavation + Haul cost = $0.3287 + $0.346 = $0.6474 per bcy

2. Determination of productivity and cost for sand and gravel

Maximum digging depth for hoe =22 ft

Depth of excavation = 12 ft

% Depth = 12/22 = 55%

Angle of swing = 80^o

Hence the hoe is working above average conditions (As per conditions stated in table 9.5)

Q = 2 cy

F = 102.5% =1.025 (Average value for sandy clay from table 9.4)

E = 45 min per hour

t = 19 sec (due to angle of swing is 80^o, additional 2sec per cycle assumed)

S = 14% = 0.14

Hence,

3600 x 2 x 1.025 x 45 Productivity P = 19 x 60 x (1 + 0.14) y = 19 x 60 X (1+0 14 = 255.5402 cy/hour

The above productivity falls under condition 2. Hence haul cost shall be $0.377 per bcy

Cost of hoe per hour = $109

Cost of excavation per cy = $109 407 = $0.4265per cy

Total Cost for sand and gravel = Cost of excavation + Haul cost = $0.4265 + $0.377 = $0.8035 per bcy

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