Question

A GC needs to fill and compact a trench that has the following dimensions 150 x 50 x 1.5 ft.   The sub is going to use a dump truck that can carry 12 CY, and travels at an average speed of 40 mph. The borrow pit is located 45 miles from the construction site. The truck driver makes $50/hr and works 8 hours per day. Loading time for the truck is 30 minutes and unloading time is 5 minutes. The sub has to rent the truck at $500 per day + a driver @ $50/hour. The cost of soil $20 per BCY. The soil has a swell factor of 18% and a compaction factor of 12%.

How much will the driver cost?

Answer 1

Step 1 : Number of trips required to fill and compact the trench

Volume of pit = 150 * 50 * 1.5 ft³ = 11250ft³ = 416.67 CY

We need 416.67 CCY to fill and compact a trench. [CCY = compacted cubic yards]

Truck carries the load in LCY[loose cubic yards].

Thus convert CCY to LCY to determine number of trips required.

LCY = CCY [ (1+ Swell) / (1 - shrinkage)]

Given swell factor = 18% = 0.18

shrinkage factor = 12 % = 0.12

Load in LCY = 416.67 [ (1+0.18)/ (1-0.12) ] = 558.72 LCY

Capacity of dump truck per trip = 12 LCY

No of trips = 558.72 / 12 = 46.5 trips = 47 trips

Step 2 : Total travel time for 1 trip

Truck travel time from construction site to pit = 45 mph/ 45 miles = 1.125hr

loading time = 30 minutes = 0.5 hr

Truck travel time from pit to construction site = 1.125hr

unloading time = 5min = 0.0833 hr

Total travel time for 1 trip = 1.125 + 0.5 + 1.125 +0.083 = 2.833 hr

Step 3 : Number of trips driver can make per day

He can work maximum of 8 hours per day

Thus, No. of trips per day = 8 / 2.833 = 2.82 = 2 trips

We approximated to lower number because the truck driver does not work for more than 8 hours.

Step 4 : Number of days to get required material.

Total number of trips = 47 trips

Number of trips per day driver can make = 2 trips / day

Thus, Number of days = 47 / 2 = 23.5 days

Step 5 : Cost of driver per day

The truck driver makes 2 trips per day.

Working time in 1 day= 2 * 2.833 hr = 5.666 hr = 5.7 hr

Charge of driver = $50 / hr

Cost of driver for 1 day = 5.7 * 50 = $285

Step 6 : Driver cost

Cost of driver per day = $ 285

For 23.5 days, cost = $285 * 23.5  = $ 6697.50

Thus, the driver cost will be $6697.50