What is the minimum length for a straight edge used in soil compaction tests?

The minimum length for a straight edge used in soil compaction tests is 10 inches. This length is specified to ensure that the straight edge is long enough to provide an accurate assessment of the surface of the compacted soil. A straight edge that is too short may not adequately span across any undulations or imperfections in the soil surface, leading to inaccurate measurements of the compaction level. Using a 10-inch straight edge strikes a balance between manageability and effectiveness, allowing for reliable results when evaluating the uniformity and flatness of the compacted layer. This is particularly important in construction and civil engineering, where proper compaction is critical for the stability and durability of structures built on or within the soil.