Is it true that placing two feet of fill and compacting it all at once is better than filling and compacting in 6" lifts?

Placing fill materials in 6-inch lifts and compacting each layer separately is generally the best practice in construction and earthwork projects. This method allows for better control of compaction, ensuring that each layer is adequately compacted before the next is placed on top.

When fill is placed in thicker layers, such as two feet, it becomes challenging to achieve uniform compaction throughout the entire depth. This can lead to weak spots, excessive settlement, and potential structural issues in the future. Compaction is most effective when the material can be thoroughly worked and densified, which is easier to achieve with thinner layers.

By filling in smaller layers, each lift can be compacted separately to the required density, producing a more stable foundation and reducing the risk of post-construction settlement. This method is particularly important in areas with varying soil conditions, where controlling the compaction of individual layers mitigates the chances of compressible zones affecting the integrity of the fill.

Therefore, the recommendation for 6-inch lifts is based on achieving optimal density and stability in the fill, making it the preferred approach in engineering practices for maintaining structural integrity.