How can the compaction of sandy soil be increased?

Increasing the compaction of sandy soil effectively can be achieved through the application of water and vibration. Sandy soil has large particles with high permeability, which often leads to less cohesion and makes it more challenging to compact. When water is added to sandy soil, it helps fill the voids between the soil particles and provides temporary cohesion. This effect allows for better interlocking of the particles during compaction.

Vibration enhances this process by further forcing the sand particles closer together and facilitating the rearrangement of the soil structure. This combination of moisture and mechanical energy promotes the densification of the sand, resulting in an increased compaction level.

While adding gravel, using heavier machinery, and mixing with clay can affect soil properties, they don't specifically enhance the compaction of sandy soil as effectively as the approach involving water and vibration. Each of those alternatives has its own set of implications for the soil mechanics and overall project requirements. For sandy soil, leveraging the characteristics of water and vibration will yield the most efficient results for compaction.