Why is drainage planning critical in earthwork?

• A. It increases soil permeability
• B. Proper drainage prevents erosion, reduces instability, and maintains pavement performance
• C. It reduces the need for subgrade preparation
• D. It accelerates sequencing by skipping drainage installation

Answer: (B)

Water control is essential in earthwork because moisture directly governs soil strength and stability. When water accumulates in or on the soil, pore pressures rise and shear strength falls, making slopes prone to movement, embankment failures, and excessive settlement. Drainage planning helps remove surface water and groundwater, keeping the subgrade dry and stable, which prevents erosion and maintains the integrity of the earthwork. It also supports pavement performance by reducing moisture-related weakening of the foundation, minimizing rutting and frost-related distress, and extending pavement life.

Drainage design typically includes surface drainage features to carry away runoff and subsurface drainage to relieve pore pressure beneath the layers. Without these provisions, the site remains vulnerable to erosion, instability, and premature pavement issues, regardless of other work that might be done.