Thickness proportioning: If d is the economic designed depth of a rigid pavement slab, what thickness is kept at the interior of the cement concrete slab?

Introduction / Context:
In cement concrete pavements, designers sometimes express practical slab thickness at different locations (interior, edge, corner) as proportions of an economic design depth. This recognizes that stress conditions vary with load position and support conditions.

Given Data / Assumptions:

• d denotes an economic design depth derived from stress criteria.
• Interior region experiences lower stress than edge/corner for the same load.
• Practical construction thicknesses include allowances and standardization.

Concept / Approach:

Empirical–analytical practice leads to guideline multipliers for interior thickness to ensure adequate safety and constructability. A commonly used proportion is about 1.125 d for the interior, accommodating construction tolerances and ensuring performance across variable support conditions.

Step-by-Step Reasoning:

Verification / Alternative check:

Worked examples in rigid pavement design frequently round or standardize thickness upward from theoretical depth, leading to factors near 1.10–1.15 for interior zones, hence 1.125 d is a representative design proportion.

Why Other Options Are Wrong:

• 1.275 d: excessive for interior; closer to edge/corner conservatism.
• 0.85 d, 0.75 d, 0.60 d: un-conservative; would reduce thickness below economic depth.

Common Pitfalls:

• Using the same thickness factor for corner, edge, and interior; corner often governs.

Final Answer:

1.125 d.