In the Cover Zone, what density is required when the top of the pipe is 15 inches below the bottom of the base?

In the Cover Zone, what density is required when the top of the pipe is 15 inches below the bottom of the base?

• A. 100% of AASHTO T-99
• B. 95% of AASHTO T-99
• C. 80% of AASHTO T-99
• D. 90% of AASHTO T-99

Answer: (A)

In the area immediately around buried pipes, the fill must be compacted to the maximum density specified by AASHTO T-99 to provide a stiff, uniform foundation for the overlying pavement. A top-of-pipe depth of 15 inches places the material squarely in the Cover Zone, where the requirement is full 100% relative compaction of the AASHTO T-99 maximum dry density. Achieving this density helps prevent differential settlement and pipe movement under traffic loads by ensuring the surrounding soil is as dense as the lab-determined maximum. Lesser percentages are used in other zones or circumstances, but not in this Cover Zone condition.

In the area immediately around buried pipes, the fill must be compacted to the maximum density specified by AASHTO T-99 to provide a stiff, uniform foundation for the overlying pavement. A top-of-pipe depth of 15 inches places the material squarely in the Cover Zone, where the requirement is full 100% relative compaction of the AASHTO T-99 maximum dry density. Achieving this density helps prevent differential settlement and pipe movement under traffic loads by ensuring the surrounding soil is as dense as the lab-determined maximum. Lesser percentages are used in other zones or circumstances, but not in this Cover Zone condition.