--- title: "Proportioning of retaining walls" subject: "Foundation Engineering" chapter: 3 key: "semester_5/foundation_engineering:proportioning-retaining-walls" source: https://www.bctengineer.com/q/semester_5/foundation_engineering/proportioning-retaining-walls site: BCT Engineering --- # Proportioning of retaining walls Foundation Engineering · Chapter 3: Lateral Earth Pressure Theories and Retaining Walls - Asked in: 2075 Chaitra, 5 marks; 2076 Asoj, 5 marks; 2072 Chaitra, 5 marks (asked 3 times) - Video: [Proportioning of Cantilever Retaining Wall ll Preliminary Dimensions of Retaining Wall #5](https://www.youtube.com/watch?v=D6cuLYTGSMA) — Uzair Khan - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/proportioning-retaining-walls - Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-3 ## Question How can the different retaining walls be proportioned (tentative dimensions of cantilever retaining walls)? ## Short answer For a cantilever wall of height H, base width 0.5H–0.7H, base slab thickness H/12–H/10 (min 300 mm), stem top 200–300 mm, stem base thickness H/12–H/10. Toe projection about B/3, heel the remainder. Shear key depth 0.1H–0.15H if needed. Foundation depth ≥ 1 m. ## Answer Tentative dimensions are assumed from the wall height $H$ (including the footing depth) from past experience, then checked for stability and revised. #### Gravity (masonry/plain concrete) wall - Top width: 0.3 m minimum (about $H/12$ to $H/6$ up to 0.6 m). - Base width: $B = 0.5H$ to $0.7H$. - Thickness of base slab: about 0.3 m or $H/8$ to $H/6$. - Front face vertical or battered (1 in 10 to 1 in 5). #### Cantilever wall (reinforced concrete) - **Base width:** $B = 0.5H$ to $0.7H$ (0.4H to 0.5H if no surcharge and good soil). - **Base slab thickness:** $H/12$ to $H/10$ (not less than 300 mm). - **Stem thickness at top:** 200-300 mm minimum; at the base $H/12$ to $H/10$ (about equal to base slab thickness). - **Toe projection:** $B/3$ (about 0.25B to 0.3B); the remainder is the heel. - **Shear key** (if sliding governs): depth about $0.1H$ to $0.15H$ below the base, under the stem. - Depth of foundation $D_f$: not less than 1 m or below frost and scour depth. ```text <--0.3m--> | stem | backfill | | H | | | H/12 | _____|________|_______________ |toe | heel | |B/3 | | base slab H/12..H/10 |<-------- B = 0.5-0.7H ----->| ``` #### Counterfort/buttress wall ($H > 6$ m to 8 m) - Base width: $0.5H$ to $0.6H$; slab and stem thickness $H/20$ to $H/15$ (200-300 mm min). - Counterfort spacing 0.3H to 0.6H (about 2.5-3.5 m), counterfort thickness 250-400 mm. - Counterforts on the backfill side (tied to stem and heel); buttresses on the front side (rarely used). Trial section is then checked for overturning ($FS \ge 2$), sliding ($FS \ge 1.5$), bearing and tension at the base. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Typical base width B of a cantilever retaining wall of height H is: A. 0.1H to 0.2H B. 0.5H to 0.7H C. 1.0H to 1.5H D. H/12 Answer: B. Base width is taken as 0.5H to 0.7H. (Key point: Base width) 2. The toe projection of a cantilever wall is about: A. B/3 B. B/2 C. 2B/3 D. H/2 Answer: A. The toe is about B/3 and the remainder of the base is the heel. (Key point: Toe projection) 3. Base slab thickness of a cantilever wall is usually: A. H/3 to H/2 B. H/12 to H/10, not less than 300 mm C. H/30 D. 0.7H Answer: B. Base slab is H/12 to H/10 with a minimum of 300 mm. (Key point: Slab and stem thickness) 4. When is a shear key provided and how deep is it? A. When overturning governs; 0.5H B. When bearing governs; 0.3H C. When sliding governs; about 0.1H to 0.15H below the base D. Never in cantilever walls Answer: C. A shear key under the stem is added when sliding governs, depth about 0.1-0.15H. (Key point: Shear key) 5. What is done with the assumed tentative dimensions? A. They are final B. They are checked for overturning, sliding, bearing and tension, then revised C. Only structural strength is checked D. They are used only for gravity walls Answer: B. Trial sections are checked for stability and revised if needed. 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