Cantilever Retaining Wall FULL Design Example | Part 1| Learn Engineering

Structural Parameters & Design Basis
📌 The design focuses on a cantilevered retaining wall with a total height of 20 feet and a base width of 12 feet, analyzed using a 1-foot unit strip approach.
⚖️ Key soil properties include an equivalent active fluid pressure of 30 psf and a passive pressure of 450 psf, with a coefficient of friction of 0.4 for sliding resistance.
🏗️ The live load surcharge is modeled as an equivalent of 2 feet of additional soil, totaling a surcharge pressure of 60 plf.

Global Stability Calculations
📐 Stability is evaluated using Allowable Stress Design (ASD) with a load factor of 1.0, focusing on the resultant gravity loads to simplify moment calculations about the toe (Point A).
🧱 The total resisting gravity load is calculated at 27,348 lbs, which includes the weight of the wall stem, base, key, retained soil, and surcharge.
🔄 The overturning demand is calculated at 6,315 lb-ft, while the resisting moment is derived from the resultant arm of 7.37 feet from the toe.

Stability Checks & Factor of Safety
✅ The factor of safety for overturning is determined by the ratio of the Resisting Moment to the Overturning Moment, resulting in a value of 3.17.
🛡️ Since the calculated 3.17 significantly exceeds the IBC minimum requirement of 1.5, the design satisfies global stability criteria for overturning.
💡 The primary mechanism of stability in cantilevered walls is the downward gravity load acting on the heel, which effectively counteracts the active soil pressure attempting to rotate the structure.

Key Points & Insights
➡️ Simplify complex structures by calculating the resultant gravity load and its corresponding centroid (x̄); this reduces the need to track individual component moments separately.
➡️ Always account for the triangular loading distribution of soil pressure (proportional to depth) alongside rectangular distributions from surcharges to ensure accurate total force summation.
➡️ When designing, ensure your factor of safety (Resisting Moment / Overturning Moment) meets the 1.5 minimum threshold mandated by building codes like the IBC to ensure long-term structural integrity.

📸 Video summarized with SummaryTube.com on Mar 24, 2026, 11:48 UTC