The Proctor theory is when compaction is achieved how?

• A. by inputting energy to expel air and water in the soil voids.
• B. By vibrating the surface only.
• C. By freezing the soil to set particles.
• D. By adding more water to soften material.

Answer: (A)

Compaction happens when soil particles are packed more tightly by applying energy that pushes air and water out of the voids between particles. In the Proctor test, a controlled amount of energy is delivered to the soil (through hammer blows in a mold), causing the particles to rearrange into a denser arrangement. As air and free water are expelled, the dry density increases, reaching a maximum at the optimum moisture content. That energy-driven expulsion of air and water from the voids is what the Proctor method measures. The other ideas—merely vibrating the surface, freezing the soil, or adding more water to soften it—don’t describe the process of using energy to reduce voids and increase density.