Difficulty: Easy
Correct Answer: -5 mm to +5 mm
Explanation:
Introduction:Tolerances ensure constructability without compromising performance. For massive elements like footings, small dimensional variations are inevitable but must be limited to avoid capacity or cover issues.
Given Data / Assumptions:
Concept / Approach:
Depth deviations affect bearing area, cover, and reinforcement position. A pragmatic yet tight tolerance for a 1 m thick footing is within ±5 mm for formwork depth, aligning with quality control expectations on major foundations.
Step-by-Step Solution:
1) Identify element scale → thick footing, not a thin slab.2) Adopt a realistic tolerance that site teams can achieve with steel/ply formwork and proper leveling.3) Choose ±5 mm as acceptable without affecting bearing safety significantly.Verification / Alternative check:
Rebar cover checks and cube level measurements typically keep variation within this band for heavy foundations when supervised.
Why Other Options Are Wrong:
±2–4 mm are impractically tight for 1 m thickness; ±10 mm may be permissible in some specs, but is looser than the recommended tolerance here.
Common Pitfalls:
Neglecting settlement or uplift of formwork during concreting and not re-checking levels after initial pour.
Final Answer:
-5 mm to +5 mm
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