Which property does compaction increase?

• A. Porosity
• B. Bulk density
• C. Infiltration rate
• D. Air content

Answer: (B)

Compaction makes soil particles pack more tightly, so the amount of solid material per given volume goes up. Bulk density is the mass of dry soil divided by the total soil volume (including any pore spaces). When soil is compacted, the volume shrinks and air is squeezed out, while the solid mass stays roughly the same, raising the bulk density. At the same time, porosity and air-filled voids decrease, and infiltration tends to slow because the pore pathways become smaller and less connected. So the property that increases with compaction is bulk density, while porosity and air content decrease and infiltration rate typically declines.