Which backfill material can achieve maximum density with minimal compaction in a moisture-saturated condition?

The correct choice is sand, as it possesses unique properties that allow it to achieve maximum density with minimal compaction, especially under moisture-saturated conditions. Sand consists of granular particles that have a relatively uniform size and shape, enabling them to move freely and settle compactly when wet. When saturated, sand particles can rearrange themselves more easily than finer materials, allowing air to escape and water to fill the voids, leading to a denser configuration without excessive external compaction effort.

In contrast, clay tends to hold moisture tightly due to its fine particle size and plasticity, requiring significant compaction to achieve high density. Gravel, while it can achieve good drainage and density, typically requires compaction as well and can create more voids in a saturated state. Silt, similar to clay, retains water and does not compact as efficiently when wet, often leading to weaker and less stable backfill. Therefore, sand’s characteristics make it the most suitable material for achieving maximum density with less compaction when saturated.