In which zone should the soil be compacted to approximately match the density of the soil in which the trench was cut?

In which zone should the soil be compacted to approximately match the density of the soil in which the trench was cut?

• A. Top Zone
• B. Bedding Zone
• C. Lowest Zone
• D. Cover Zone

Answer: (C)

When backfilling a trench, you want the density of the fill to match the native soil to avoid settlement differences and ensure a stable interface. The lowest zone—the layer at the bottom where the new fill sits directly on undisturbed soil—is the critical area to compact to approximate the original density. Getting this bottom layer right helps prevent differential settlement that could affect the trench and any pipe or structure inside. The other zones around the pipe (bedding, cover, and top) also need good compaction, but matching the in-situ density at the lowest point is the key to a stable, uniform backfill.

When backfilling a trench, you want the density of the fill to match the native soil to avoid settlement differences and ensure a stable interface. The lowest zone—the layer at the bottom where the new fill sits directly on undisturbed soil—is the critical area to compact to approximate the original density. Getting this bottom layer right helps prevent differential settlement that could affect the trench and any pipe or structure inside. The other zones around the pipe (bedding, cover, and top) also need good compaction, but matching the in-situ density at the lowest point is the key to a stable, uniform backfill.