The code minimums and design-guide criteria for cantilever, gravity, segmental block, geogrid-reinforced and soil nail walls on one card. Local amendments and owner standards (DOTs, municipalities) often tighten these — check the governing document.
IBC §1807.2.3 — Code minimum for all retaining walls
Check
Static
With earthquake loads
Sliding
1.5
1.1
Overturning
1.5
1.1
§1807.2.1 also requires stability against excessive foundation pressure and water uplift. Common practice for gravity and cantilever walls is 2.0 on overturning, with the resultant within the middle third (e ≤ B/6) on soil.
Moist soil at optimum density. Saturated or submerged backfill: buoyant soil weight plus full hydrostatic pressure. Walls free to deflect use active; walls restrained at the top (e.g. basement walls braced by a floor) generally use at-rest — see §1610.1 for the exact conditions. A geotechnical investigation may replace these values.
As adopted in the Town of Clayton, NC Segmental Block Retaining Wall Design standard, Table 2.1 (critical structures), which follows the NCMA Design Manual for Segmental Retaining Walls. The same standard sets a 2,000 psf minimum bearing capacity and a 1% differential settlement limit (evaluate for walls 10 ft and taller).
Geogrid-reinforced walls — geometry and pullout
Item
Value
Source
Minimum reinforcement length (MSE walls)
0.7H
FHWA-NHI-10-024 §4.2
Minimum length, all but highway loading
0.6H
Clayton NC Table 2.1
Minimum length, AASHTO highway loading
0.7H or 8 ft, greater
Clayton NC Table 2.1
Scale-effect factor α, geogrids / geotextiles (no test data)
0.8 / 0.6
FHWA-NHI-10-024 Table 3-6
Kr/Ka for geosynthetic (extensible) reinforcement
1.0, constant with depth
FHWA-NHI-10-024 §4.4
Design surcharges (live load on the retained side)
Use above the wall
Surcharge (psf)
Landscaping walls
0
Pedestrian traffic, light storage
50
Light traffic, auto parking
100
Highway loading, heavy traffic
250
FHWA minimum traffic surcharge (MSE walls)
2 ft of soil
Tiered walls: an upper wall set back less than about 2× the lower wall's height (face to face) surcharges the lower wall and must be included in its design (Clayton NC Table 2.1, note 1).
Soil nail walls — FHWA GEC 7 Table 5.1 (ASD)
Limit state
Static
Seismic
Overall stability (1.35 for some non-critical permanent walls)
1.5
1.1
Overall, temporary excavation lift
1.25–1.33
—
Basal heave (short term / long term)
2.0 / 2.5
2.3
Pullout
2.0
1.5
Lateral sliding
1.5
1.1
Bar tension, Grade 60/75 | Grade 95/150
1.8 | 2.0
1.35 | 1.50
Facing flexure / punching shear
1.5
1.1
Measured maximum nail force (GEC 7 §5.4): 0.5–1.1 KaγHSvSh in the upper two-thirds, averaging about 0.75; the lower third carries about half that. Presumptive bond strengths by soil and drilling method: see the soil nail calculator.
Cantilever wall — first-trial proportions
Dimension (H = total height)
First trial
Base width, B
0.5H – 0.7H
Toe length
≈ B/3
Footing thickness
≈ 0.1H, 12″ min
Stem at base / at top
≈ 0.08–0.1H / 8–12″
ACI 318-19 min. flexural steel (Gr 60) / max. spacing
0.0018Ag / min(3h, 18″)
Sources: International Building Code §1807.2 and §1610, Table 1610.1 (ICC); FHWA-NHI-14-007, Soil Nail Walls Reference Manual (GEC 7, 2015), Table 5.1 and §5.4; FHWA-NHI-10-024, MSE Walls and Reinforced Soil Slopes, Vol. I (2009); Town of Clayton, NC, Segmental Block Retaining Wall Design (2010), Table 2.1, following the NCMA Design Manual for Segmental Retaining Walls; ACI 318-19 Table 7.6.1.1 and §7.7.2.3. Proportions are customary first trials, not requirements.