Which Proctor test is typically used for embankment and structure backfill materials?

• A. In-Situ
• B. Standard
• C. Modified
• D. California Bearing Ratio

Answer: (B)

The main idea is how different Proctor tests use different compaction energies to find the moisture content at which a soil reaches its maximum dry density. For typical embankment and structure backfill, the standard Proctor is used because it represents ordinary compaction energy applied to general fill materials. It provides a practical, economical basis for specifying moisture content and achievable density in common fills, which is usually sufficient for backfill under structures and along embankments.

The modified Proctor uses higher energy to reach a higher maximum dry density and is chosen when greater strength or lower settlement is required, such as for heavy traffic subgrades or particularly challenging soils. The in-situ case tests are field density tests, not Proctor tests, and the California Bearing Ratio is a bearing-strength test, not a Proctor test.