Calculate Roller Production

An excavating contractor determined through a test strip, that a smooth steel-wheel vibrating roller compactor operating at 3-mph can compact a 6-inch layer of borrow material to a proper density in four passes. The width of the smooth steel drum is 8.0-ft and operates 50-min per hour.   The number of compacting rollers required to maintain a material delivery rate of 540-bank cubic yards per hour is most nearly (1 bank cubic yard = 0.83 compacted cubic yards):

Solution: Calculate roller production.

Step 1: Compute a conversion factor to standardize the various units of measure:

(5280 ft/mile) x (1 cubic yard / 27 cubic feet) x (1 foot / 12 inches) = 5280/27/12 = 16.3

Step 2: Compute compacted cubic yards (CCY) per hour:

Compacted cubic yards per hour = (16.3 x 8-ft x 3-mph x 6-inch x 50-min/60-min) ÷ 4 passes = 489 CCY/hr

Step 3: Compute compacted cubic yards (CCY) per hour to bank cubic yards (BCY)

489-CCY/hr ÷ 0.83-CCY/BCY = 589.2 bank cubic yards per hour

Step 4: Compute the number of roller compactors needed.

Thus, 540 BCY/hr ÷ 589.2 BCU/hr = 0.92 < 1-roller compactor  

Therefore, only one roller is required to keep up with the delivery of borrow material.