What generally occurs with the angle of internal friction as soil compacts?

As soil compacts, the angle of internal friction generally increases. This phenomenon occurs due to the rearrangement of soil particles closer together during the compaction process. As the particles are forced into a denser configuration, their interlocking improves, which enhances the resistance to sliding between the grains. Consequently, the effective stress within the soil increases, leading to a higher angle of internal friction, which is essentially a measure of the shear strength of the soil. This increase in friction contributes to greater stability and strength in the compacted soil mass, making it more suitable for construction and other engineering applications.

This behavior is fundamental in geotechnical engineering, where understanding the properties of soil before and after compaction can significantly affect the design and safety of structures built on or within the ground.