Cantilever Retaining Wall with 10 ft Backfill per ACI 318-25 & IBC 2024

Example

A cantilever concrete retaining wall retains 10 ft of SM silty-sand backfill with a 100 psf surcharge. Geometry: 12 in uniform stem, 3 ft toe, 6 ft heel, 18 in footing, 1 ft of soil over the toe, and a 12×12 in shear key. Soil: γ = 120 pcf, μ = 0.35, passive lateral bearing 200 psf/ft, allowable bearing 3,000 psf. Verify stability per IBC 2024 §1807.2.3 (FS ≥ 1.5) and design the stem, heel, and toe per ACI 318-25.

How StructSuite solves this

StructSuite's free structural design software applies the design lateral soil load from IBC 2024 Table 1610.1 (SM, active: 45 psf/ft — ASCE 7-22 Table 3.2-1 is also offered verbatim), checks overturning and sliding at 1.0 × nominal loads with the surcharge investigated driving-only (IBC §1807.2.3), combines friction, and passive resistance over the key depth (§1806.3.1), computes the kern-aware bearing distribution, then designs the stem as a one-way slab at the stem–footing interface (ACI 318-25 §13.3.6.1.1, §13.3.6.3), the heel with shear taken at the face (§7.4.3.2), and the toe from the governing 1.2D + 1.6H + 1.6L / 0.9D + 1.6H factored bearing (§5.3.8; ASCE 7-22 §2.3.1), finishing with hooked-dowel development (§25.4.3.1) and minimum reinforcement (Table 11.6.1, §24.4.3.2).

Steps

1. Step 1: Geometry & Configuration

   Design consideration: Rule-of-thumb proportions for a first pass: footing width B ≈ 0.5–0.7 × total height (here B = 10 ft ≈ 0.87 × 11.5 ft — generous because of the surcharge), footing thickness ≈ 10% of total height, toe ≈ B/4. The 12×12 in key is what carries the sliding check past FS 1.5 here — without it the passive depth is only 2.5 ft and FS falls to 1.35.

   In StructSuite: Open Step 1: Geometry & Configuration. In Stem height (ft) enter 10; in Retained height (ft) enter 10; in Stem thickness (in) enter 12; in Footing thickness (in) enter 18. Enter Toe length (ft) 3 and Heel length (ft) 6, and Soil cover over toe (ft) 1. Turn on Shear key and enter its width and depth if the sliding check needs the extra passive depth.

2. Step 2: Soil & Lateral Earth Pressure (IBC 2024 §1610 / ASCE 7-22 §3.2)

   Design consideration: SM silty sand is a common granular backfill: IBC Table 1610.1 gives 45 psf/ft active vs 60 at-rest. A free-standing cantilever wall may use active (§1610.1). Note ASCE 7-22 Table 3.2-1 tabulates the same SM class at 45 psf/ft active but other classes differ between the books — pick the table your jurisdiction enforces. The 100 psf surcharge is a typical light traffic/storage allowance.

   In StructSuite: Open Step 2: Soil & Lateral Earth Pressure. Choose the design lateral soil load source — IBC 2024 Table 1610.1, ASCE 7-22 Table 3.2-1, or the geotechnical equivalent fluid pressure — and select the backfill class row in the table. Pick Active or At-rest per IBC §1610.1. Enter Soil unit weight (pcf) 120, Uniform surcharge (psf) 100, Coefficient of friction 0.35, Passive lateral bearing (psf/ft) 200, and Allowable bearing pressure (psf) 3000 (or select an IBC Table 1806.2 presumptive row to fill them).

3. Step 3: Concrete & Reinforcement (ACI 318-25)

   Design consideration: f'c = 3,000 psi and Grade 60 bars are typical for site retaining walls. Covers: 3 in cast against earth (footing bottom), 2 in formed against earth (stem earth face, footing top) per Table 20.5.1.3.1. #6 @ 8 in stem bars give As = 0.66 in²/ft — more than twice the 0.259 in²/ft minimum, and the section stays tension-controlled.

   In StructSuite: Open Step 3: Concrete & Reinforcement. Enter f'c (psi), fy (psi), and the concrete unit weight. Enter the three covers per ACI 318-25 Table 20.5.1.3.1 (3 in cast against earth; 2 in or 1.5 in formed exposed). Select bar size and spacing for the stem vertical bars, stem horizontal shrinkage + temperature bars, heel top bars, and toe bottom bars.

4. Step 4: Design Verification (ACI 318-25 & IBC 1807.2)

   Design consideration: The governing checks here: sliding FS = 1.54 (just over 1.5 thanks to the key) and heel flexure D/C = 0.94. The stem is only at 56% — retaining walls are usually stability-governed, not strength-governed. Expand each row to read the full substituted derivation.

   In StructSuite: Open Step 4: Design Verification. The module runs overturning and sliding stability (FS ≥ 1.5 per IBC 2024 §1807.2.3), soil bearing, then the ACI 318-25 strength checks — stem flexure and shear at the interface, heel and toe design, development and hooks, and minimum reinforcement. Expand any check row to see the full substituted derivation with code citations.

Live design (pre-filled)

The form below is the real StructSuite module with example data loaded. Display only—values cannot be changed.