Which material can be used as backfill outside a foundation without requiring compaction?

• A. Controlled low strength material
• B. Gravel
• C. Sand
• D. Clay

Answer: (A)

Controlled low strength material (CLSM) is designed to be used as a backfill solution that does not require compaction. CLSM is a self-compacting concrete mix that flows easily and fills voids in trenches or excavations without the need for mechanical compaction. This is particularly advantageous in foundation work, as it helps to prevent settling and ensures a uniform load distribution around the foundation.

The other materials listed, such as gravel, sand, and clay, typically require compaction to achieve the desired stability and load-bearing capacity. For instance, while gravel may drain well and provide solid support once compacted, it cannot achieve the same performance without undergoing that process. Sand behaves similarly, needing compaction to minimize voids and increase stability. Clay can retain moisture and expand or contract with changes in moisture content, requiring careful compaction to avoid issues related to settlement or heaving.

In contrast, the ease of use and inherent properties of controlled low strength material make it an ideal choice for backfilling around foundations without additional effort for compaction.