What is the drop height for a modified proctor test?

• A. 12 inches.
• B. 24 inches.
• C. 18 inches.
• D. 6 inches.

Answer: (C)

In the Proctor compaction tests, the drop height is the distance the hammer is released from to deliver energy into the soil sample, which controls how densely you can compact the soil in the lab. The Modified Proctor test uses a higher energy than the standard version, achieved by dropping the hammer from 18 inches. This higher energy helps simulate tougher field compaction and typically yields a higher maximum dry density. That’s why 18 inches is the value used for the Modified Proctor. The other heights correspond to different protocols: 12 inches is for the Standard Proctor, 24 inches would exceed typical lab procedures for these tests, and 6 inches would provide far less energy than the Modified Proctor.