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Phase diagrams before and after compaction

Short answer

Compaction reduces air voids in dry soil by mechanical energy, while consolidation expels water from saturated soil under load. In both processes solids volume stays constant, void ratio decreases, and dry unit weight increases.

Draw phase diagrams for a dry soil sample and a saturated soil sample before and after the compaction and consolidation processes, respectively.

Compaction reduces air voids by mechanical energy (no water leaves); consolidation reduces voids by squeezing water out of saturated soil under a sustained load. Solids volume VsV_s is constant in both.

Dry soil before and after compaction

 Before            After (V reduced)
 +------+          +------+
 | Air  |          | Air  |  (less)
 |      |          +------+
 |      |          |Solids|  Vs same
 +------+          +------+
 |Solids|
 +------+

Air volume decreases, so the void ratio and total volume decrease; WsW_s is unchanged.

Saturated soil before and after consolidation

 Before            After (V reduced)
 +------+          +------+
 |Water |          |Water |  (less)
 |      |          +------+
 |      |          |Solids|  Vs same
 +------+          +------+
 |Solids|
 +------+

Water is expelled from the voids, so VwV_w and VV decrease, SS remains 100% and WwW_w decreases.

In both cases the void ratio falls and dry unit weight rises.

✓ Answer checked by Claude Opus 5.5 (high effort)

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