Which standard method describes the laboratory compaction characteristics of soil using modified effort?

The correct choice describes ASTM D1557, which outlines the laboratory compaction characteristics of soil using modified effort. This standard is crucial in determining the maximum dry density and optimal moisture content of soils when subjected to a higher compaction energy compared to other methods. The modified Proctor test, as specified in this standard, uses a heavier hammer (4.5 kg) and a greater drop height (450 mm) to compact the soil sample in a mold of a volume of 1/30 cubic meter, allowing for a more accurate representation of the compaction potential of soils subjected to heavy loads, such as those found in road construction.

This greater energy input simulates field conditions more closely, especially in high-stress areas, ensuring that the soil's structural integrity and performance under load are adequately assessed. Consequently, it provides vital data for engineers when analyzing soil's suitability for various construction projects, ensuring structures built on these soils are stable and durable. Other standards like ASTM D698, while also related to compaction, utilize standard effort, making them less appropriate for those looking to understand modified compaction characteristics.