Which density describes the weight of soils and solids occupying a unit volume?

• A. Wet Density
• B. Relative Density
• C. Bulk Density
• D. Dry Density

Answer: (D)

The main idea here is distinguishing how we express soil weight per volume depending on what is included in the weight. Dry density refers specifically to the weight of the solid soil particles per unit volume, excluding moisture and air-filled voids. In other words, it measures how heavy the solids themselves are when you look at a given volume, ignoring any water that might be present.

If water is present, the weight per volume increases and is described by the moist or wet unit weight, which includes water in the mass. A term like bulk density also includes weight per volume but typically includes both solids and water (and sometimes air is treated separately), so it isn’t just the solids’ weight per volume. Relative density, on the other hand, is a dimensionless ratio that characterizes how compact a granular soil is relative to its loosest and densest states.

So the description “weight of soils and solids occupying a unit volume” aligns with dry density—the weight contributed by the solid particles per unit total volume, without counting moisture.