Why is proper drainage essential for subgrade soil in highway pavements?

Explanation:

Subgrade Soil in Highway Pavements

1. Proper drainage is essential for subgrade soil in highway pavements to prevent the accumulation of water in the soil, which can lead to moisture retention.
2. Excess moisture can significantly weaken the subgrade by reducing its shear strength and causing expansion or contraction of the soil.
3. This can lead to cracking, rutting, and deformation of the pavement over time.
4. Effective drainage ensures that water is quickly removed from the soil, maintaining the stability and integrity of the pavement.

 Additional InformationKey Properties of Subgrade Soil:

1. Strength: The ability of subgrade soil to support traffic loads without excessive deformation or failure. This is determined by its shear strength and bearing capacity.

2. Compaction: Proper compaction of the subgrade is necessary to ensure the soil is dense enough to resist settlement under traffic loads.

3. Moisture Content: The moisture content of subgrade soil greatly affects its behavior. If it becomes too wet, the soil may become weak and lose its load-bearing capacity, while if it’s too dry, it may become overly rigid and crack.

4. Plasticity: This refers to the soil's ability to deform without cracking. Soils with high plasticity are generally less stable and more prone to shrinking and swelling.