Which property of soil increases after compaction, thereby allowing it to support heavier loads?

The property of soil that increases after compaction and allows it to support heavier loads is shear strength. When soil is compacted, the grains are brought closer together, which reduces the void spaces within the soil. This densification process not only increases the contact area between particles but also enhances the friction and interlocking characteristics of the soil grains. As a result, the soil's resistance to shear stresses—defined as shear strength—increases, making it more capable of bearing loads without failing or deforming excessively.

Shear strength is critical in determining the stability of soil under loads, making this property fundamental for soil used in engineering foundations, roadways, and other structures. For engineering applications, higher shear strength translates to improved performance of the soil, allowing it to carry higher loads and thereby enhancing the overall stability and safety of infrastructure.

In contrast, other properties such as porosity, compressibility, and plasticity do not necessarily increase with compaction. Porosity usually decreases as compaction consolidates the soil grains, while compressibility tends to decrease, indicating that the soil becomes less prone to settlement under load. Plasticity reflects the soil's behavior under varying moisture conditions and does not directly correlate with compaction in regard to load-bearing capacity.