Reference no: EM13531124
1) You are given the following information about a dry-batchpaving operation. You are going to use one mixer that has a servicerate of 30 serives/hr. The dry-batch trucks you use forbringing concrete to the paver have an arrival rate of 7.5 arrivals/hr. Each truck carries 6 cu yd of concrete. You have a totalamount of 13,500 cu yd of concrete to pour. You rent a truckat $100/hr, and the paver at $300/hr.If the job takes more than 80hrs, you pay a penalty of $700/hr owing to delays in jobcompletion. On the basis of least cost, determine the numberof trucks you should use. Plot the cost versus the number oftrucks used.
2) As a contractor, you are blasting rock out of a quarry andhauling it down to the waterfront in dump trucks to form a jetty(see picture on following page).
Quarry blasting
Blasted rock has 0.69 swell factor
Loose rock density = 1.4 tons/yd3
Blasting produces 500 yd3 of loose rock every houron average
Efficiency is already factored in to the blasting productionrate
Trucking
You have 5 off-road dump trucks to transport the rock
Capacity = 25 yd3 of loose rock each on average
Efficiency: trucks work 55 minutes out of every hour
Typical haul cycle:
5 minutes loading
8 minutes from quarry to jetty
1 minute dump
8 minutes return trip
Jetty placement
The jetty consists of 100,000 yd3 of rock materialthat you must place
Once placed, “jetty rock” has an average density of1.45 tons/yd3 in place
It takes 3 minutes for the excavator on the jetty to adjust therocks dumped by each truck so that they are properly positioned inthe jetty. The next truck cannot dump its rocks until the excavatoris done with the positioning from the previous truck.
Efficiency: excavator works 50 minutes out of every hour
Answer the following questions:
What is the density of the rock (in tons/yd3) in the bank before it is blasted out?
How many complete cycles can a truck make in 1 hour?
What is the productivity of this operation in terms ofyd3/hr of jetty rock?
How many total truck loads do you need to place all the jettyrock?
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