What does "modified effort" indicate in compaction tests?

In compaction tests, "modified effort" refers to a specific level of compactive energy applied to a soil sample, which is designed to replicate field conditions more accurately. Compaction tests, such as the Modified Proctor Test, utilize a standardized methodology where a predetermined amount of weight is dropped from a set height to compact the soil.

The correct choice indicates that the modified effort corresponds to a compactive energy of 56,000 lbf/ft³. This value is critical for determining the maximum dry density of the soil when subjected to the modified compaction method. The greater energy input results in denser soil, which is essential for various engineering applications and helps predict how the soil will perform under load.

Choosing values that are significantly lower, such as those associated with 12,400 lbf/ft³, 20,000 lbf/ft³, and 30,000 lbf/ft³, would not accurately represent the modified effort standard. These lower values are indicative of less compactive effort and are typically associated with a different compaction standard, such as the Standard Proctor Test. Understanding these differences is crucial for effective soil testing and ensuring that construction projects achieve the necessary soil properties for stability and load-bearing capacity.