Question

You are working for a contractor that has a contract for construction of a new residential building. As part of the project, you need to remove the soil for the construction of the basement and foundation for a parking garage. From the project plans you know that 7,500 bank cubic yards must be excavated and that 1200 compacted cubic yards will be required to backfill the completed foundation. You plan to stockpile the soil needed for backfill on site and haul the excess soil to a disposal site. The average haul distance is estimated to be 650 ft. with a 6% average uphill grade. The contractor had the soil tested and determined that the bank density is 2,850 pounds per cubic yard, the loose density is 2,300 pounds per cubic yard, and the compacted density is 3,285 pounds per cubic yard. What is the percent swell for the soil? What is the percent shrinkage for the soil after being compacted? How many bank cubic yards should be stockpiled to be used for backfill operation? How many loose cubic yards of soil should be hauled away to the disposal site?

Answer 1

Solution:

Since mass = density x volume, so, total mass to be excavated = bank density x bank volume

or, M = 2850 x 7500 = 21,375,000 lb

And mass of soil required for back fill = compacted density x back fill volume = 3285 x 1200 = 3,942,000 lb

So, Mass of soil to be hauled = 21,375,000 - 3,942,000 = 17,433,000 lb

So, bank cubic yard to be stockpiled = 3,942,000 / 2850 = 1383.16 yd³

And loose cubic yards to be hauled away = 17,433,000 / 2300 = 7579.56 yd³

Percent swell for the soil = = ((2850 / 2300) - 1) x 100 = 23.91%

Percent Shrinkage of soil = = (1 - (2850 / 3285)) x 100 = 13.24%