In order for a soil to become compacted, two conditions must be present, pressure and a soil that will compact . Different soils have different compaction characteristics. Sandy loam soils compact most readily; however, most soils with a high percentage of sand compact easily. Silt loam soils are more resistant to compaction, but they too are easily compacted when wet. When silt loam soils are not wet, it requires high pressure to compact them. When the soil is wet, each particle is lubricated and less pressure is required to compact the soil. Clayey soils can be compacted; but, as they dry and cracking takes place, t hey loosen themselves.
Murdock, Lloyd W., "Causes of Soil Compaction and Ways to Minimize Them" (1984). Soil Science News and Views. 175.