Proportioning of retaining walls

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.

        <--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.