To what depth below the bottom of the pipes and box culverts elevations should rock, boulders, or other hard lumpy or unyielding material be removed?

To what depth below the bottom of the pipes and box culverts elevations should rock, boulders, or other hard lumpy or unyielding material be removed?

• A. 12 inches
• B. 6 inches
• C. 18 inches
• D. 24 inches

Answer: (A)

Removing rock and other hard, unyielding material to a sufficient depth beneath pipes and box culverts creates a stable, uniform bearing surface for bedding and backfill. The required depth is twelve inches below the bottom of the pipe or culvert. This depth removes the troublesome material that could cause point loads or differential settlement, while still leaving room to place and properly compact bedding material to support the structure. If you only go six inches, unyielding material may remain in contact with the pipe, increasing the risk of settlement. Going deeper than twelve inches adds extra work and cost without providing additional benefit in normal conditions. So, twelve inches is the appropriate depth.

Removing rock and other hard, unyielding material to a sufficient depth beneath pipes and box culverts creates a stable, uniform bearing surface for bedding and backfill. The required depth is twelve inches below the bottom of the pipe or culvert. This depth removes the troublesome material that could cause point loads or differential settlement, while still leaving room to place and properly compact bedding material to support the structure. If you only go six inches, unyielding material may remain in contact with the pipe, increasing the risk of settlement. Going deeper than twelve inches adds extra work and cost without providing additional benefit in normal conditions. So, twelve inches is the appropriate depth.