Retaining wall detailing thumb rule: The thickness of the base slab of a cantilever retaining wall is generally provided as which proportion of the stem width at the base?

Introduction / Context:

In preliminary proportioning of cantilever retaining walls, designers use practical thumb rules for member thicknesses before refined analysis. The base slab must be thick enough to resist bending and shear from soil/overburden reactions while remaining economical.

Given Data / Assumptions:

• Conventional cast-in-place cantilever retaining wall.
• Proportioning at concept stage; soil and surcharge loads will be checked later.
• Stem thickness at the base is known (controls stress flow into the base slab near the heel/toe).

Concept / Approach:

Preliminary dimensions commonly adopt a base slab thickness around one-fourth of the stem thickness at the base. This provides a reasonable effective depth against flexure near heel and toe and ensures shear capacity prior to detailed design with load combinations and soil pressures.

Step-by-Step Solution:

Verification / Alternative check:

Iterative sizing with bending moment envelopes under active/passive pressures typically results in base slab thicknesses close to this rule, adjusted for material strengths and exposure conditions.

Why Other Options Are Wrong:

• 1/2 or equal or twice: Typically excessive and uneconomical for normal walls.
• 1/3: Sometimes used conservatively, but 1/4 is a more standard starting point in many handbooks.

Common Pitfalls:

• Using thumb rules without subsequent verification of heel/toe bending and shear, sliding, overturning, and bearing pressure under factored loads.

Final Answer:

one fourth of the width of the stem at the bottom