Retaining Wall Calculator, ACI 318-19

What it checks

The module designs the stability and strength of a cantilever retaining wall. It evaluates overturning, sliding, and bearing capacity against service loads using a factor of safety approach. It also performs strength design for the stem, heel, and toe elements. The design method distinguishes between stability and member strength. Stability checks follow IBC 2021 §1807.2, which requires service loads with a factor of safety. Member strength checks use load combinations, either from project inputs or ASCE 7-22 §2.3.1 factors. The module does not apply load factors to stability checks to avoid double-counting. The sequence of checks begins with calculating lateral earth pressures, including active, at-rest, and passive cases. It integrates these pressures to find resultants and lever arms. It then checks global stability for overturning, sliding, and bearing. Finally, it calculates internal forces in the stem and footing to determine required reinforcement.

Inputs

Geometry - Stem thickness at the base (in), wall height (ft), toe embedment depth (ft), and key depth (in).
Soil Properties - Moist unit weight (pcf), saturated unit weight (pcf), friction angle (deg), and backfill slope (deg).
Water Table - Depth to free water below the top of retained soil (ft). Values at or beyond wall height indicate no water table.
Pressure Models - Active pressure as equivalent fluid (pcf) or seismic lateral earth pressure (psf) from geotechnical reports.
Passive Resistance - Passive mobilization factor (fraction) and depth of soil to neglect at the toe (ft).
Load Combinations - Project load combinations for strength design. If absent, ASCE 7-22 §2.3.1 factors are used.
Seismic - Ev toggle (SDS) to fold 0.2*SDS*D into seismic combinations for factored design.

What it reports

Stability Factors - Factors of safety for overturning, sliding, and bearing compared against service load demands.
Pressure Resultants - Earth and water resultants (kips/ft) and their lever arms above the base (ft) from Simpson integration.
Stem Forces - Moment, shear, and top reaction at the stem base or supports, depending on restraint conditions.
Reinforcement Selection - Bar size number and centre-to-centre spacing (in) for each face of the stem and footing.
Steel Area - Provided steel area (in^2/ft) compared against required steel area (in^2/ft).
Spacing Limits - Maximum permitted spacing (in), capped at the lesser of 3h and 18 in per ACI 318-19.
Development Length - Straight-bar development length required (in) per ACI 318-19 25.4.2.3.
Selection Status - Boolean flag indicating if a bar size and spacing within limits satisfies the required steel area.

Code references

The engine cites ACI 318-19 §7.6.1.1, §9.6.1.2, and §25.4.2.3 for reinforcement and development length. It references IBC 2021 §1807 for stability checks and IBC 2021 Section 1803.5.12 item 1 for seismic lateral earth pressure requirements. The module also utilizes Rankine earth pressure theory and ASCE 7-22 §2.3.1 factors when project load combinations are not supplied.

Limits

The module does not implement the Mononobe-Okabe seismic active coefficient calculation, though the function exists for static Coulomb cases. Stability checks are not run through project load combinations to prevent double-counting with IBC 2021 §1807.2 service load factors. The passive mobilization factor is an engineering convention, not a code value. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

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