Highway engineering (flexible pavements): What is the minimum thickness of the base course in a flexible pavement as typically adopted in practice and IRC-based design guidelines?

Introduction / Context:
In flexible pavement design, the base course is the high-quality granular or bituminous layer placed above the sub-base and below the binder/surface. It distributes wheel loads, provides shear strength, and protects lower layers from excessive stress. Knowing the minimum practical thickness helps ensure durability and constructability in highways and rural roads.

Given Data / Assumptions:

• Pavement type: flexible (granular or bituminous base).
• Standard practice under IRC-style design with normal traffic categories.
• Question asks for a typical minimum, not a project-specific structural requirement.

Concept / Approach:

Minimum thickness is governed by constructability, aggregate interlock requirements, and resistance to construction damage. While the structural design may sometimes demand greater thickness, the base course is rarely allowed thinner than a commonly accepted practical minimum because very thin bases segregate easily and cannot develop adequate interlock and stiffness.

Step-by-Step Solution:

Verification / Alternative check:

Design charts may yield thicker bases for heavier traffic or weak subgrades; however, when the computed thickness is below 10 cm, it is typically rounded up to at least 10 cm to satisfy construction quality and durability needs.

Why Other Options Are Wrong:

• 15 cm, 20 cm, 25 cm, 30 cm: These may be used for heavier traffic conditions, but they are not the common minimum practical thickness.

Common Pitfalls:

• Confusing minimum base thickness with minimum sub-base thickness or total crust thickness.
• Assuming a thin base is acceptable because a thick sub-base is provided; the base has distinct functional requirements.

Final Answer:

10 cm.