This is a preliminary, educational stability check for a simplified cantilever/gravity retaining wall — it is not a substitute for an actual geotechnical report and a licensed engineer's design. It uses a simplified rectangular-stem geometry, ignores passive resistance and toe embedment, and does not check structural (stem/footing) reinforcement, seismic loading, or global slope stability. Real designs require a site-specific geotechnical investigation and a full structural calculation sealed by a licensed engineer.
When to use: Quick preliminary screening of a cantilever/gravity retaining wall against the three standard stability checks using Rankine active earth pressure — Ka = tan²(45° − φ/2), active force Pa = 0.5·Ka·γ·H² acting at H/3 above the base. Enter your assumed wall geometry and soil parameters to see overturning, sliding, and bearing pressure factors of safety.
Reminder: this is a preliminary/educational screening tool only. It does not replace a site-specific geotechnical report, a full structural design (stem and footing reinforcement, drainage design, seismic loading, global slope stability), or review and stamping by a licensed engineer.
This calculator runs the three standard preliminary stability checks for a cantilever or gravity retaining wall — overturning, sliding, and bearing pressure/eccentricity — using classical Rankine active earth pressure theory. It is intended for early conceptual screening and engineering education, not for construction documents. For the underlying wall-type selection and lateral earth pressure theory in more depth, see the companion Retaining Wall Design guide.
Rankine (1857) earth pressure theory assumes the wall deflects slightly away from the retained soil, allowing the backfill to reach its active state. The active earth pressure coefficient is Ka = tan²(45° − φ/2), where φ is the backfill's internal friction angle. For a wall of height H retaining soil of unit weight γ, the pressure increases linearly with depth and the total active thrust per unit length of wall is Pa = 0.5 · Ka · γ · H², acting at H/3 above the base of the wall (the centroid of the triangular pressure distribution). A uniform surcharge behind the wall (e.g., a parking area or roadway) adds a second, rectangular pressure block of Ka · q_surcharge over the full height, acting at H/2.
Higher friction angles produce lower Ka and therefore lower active pressure — dense, well-graded granular backfill with φ around 30–36° is strongly preferred over silty or clayey backfill, which can have φ as low as 20–25° and roughly double the design thrust.
Overturning stability compares the resisting moment — the wall's own weight (stem, footing, and the backfill soil sitting on the heel) acting through their centroids about the toe — against the overturning moment created by the active thrust acting at H/3 (or H/2 for a surcharge component) above the base. A factor of safety of at least 2.0 against overturning is the standard preliminary target.
Sliding stability compares the resisting force — base friction, calculated as the total vertical load times an assumed friction coefficient between the footing concrete and the founding soil — against the horizontal driving force from active earth pressure. A factor of safety of at least 1.5 is the standard target; this calculator conservatively ignores passive resistance from soil embedment in front of the toe and does not include a shear key, both of which a full design could use to improve a marginal sliding result.
Bearing pressure stability locates the resultant of all vertical loads relative to the footing width, computes the eccentricity e from the footing centerline, and checks it against the middle-third rule (e ≤ B/6). Within the middle third, the footing remains fully in compression and the maximum toe pressure is q_max = (ΣV/B)·(1 + 6e/B); outside the middle third, only part of the footing bears and pressure concentrates sharply at the toe. The computed q_max must not exceed the allowable soil bearing pressure from a geotechnical report (or a conservative presumptive value for preliminary work).
To keep this tool usable for quick preliminary screening, it makes several simplifying assumptions that a final design must revisit: the stem is modeled as a uniform rectangular thickness rather than the tapered profile typical of an efficient cantilever stem; passive soil resistance in front of the toe and any shear key are ignored (conservative for sliding); soil weight above the toe is ignored; hydrostatic (water) pressure behind the wall is assumed to be zero, which requires a properly functioning drainage system; and seismic (dynamic) earth pressure, structural reinforcement design of the stem and footing, and global (deep-seated) slope stability are not evaluated at all.
This tool is therefore appropriate for early feasibility checks, learning how the Rankine method and stability checks fit together, and sanity-checking a rough geometry before a formal design — not for construction drawings or permit submittals.
Start with an assumed geometry: a common starting point for a cantilever wall is a total base width of roughly 0.5–0.7 times the retained height, with the toe taking up about a third of the base width. Enter your backfill unit weight and friction angle (use actual geotechnical report values if available, otherwise the typical defaults are reasonable for granular fill), your assumed base friction coefficient, and the allowable bearing pressure from a geotechnical report. If any of the three checks fail, try widening the base, shifting more width to the heel (increasing the resisting moment and vertical load for friction), or increasing the footing/stem thickness — then verify the revised geometry with a geotechnical and structural engineer.
Standard allowable-stress-design (ASD) practice targets a factor of safety of at least 2.0 against overturning and at least 1.5 against sliding. Some jurisdictions and geotechnical reports specify different values, and LRFD-based codes use load and resistance factors instead of a single lumped factor of safety — always confirm the governing criteria for your project with the engineer of record.
Passive resistance depends on the embedment depth in front of the wall actually staying in place over the structure's life — it can be removed by future excavation, erosion, or grading changes that a preliminary tool cannot anticipate. Ignoring it is conservative and is a common simplification for early screening; a full design can credit passive resistance (and a shear key, if needed) when embedment is guaranteed by the final grading plan.
The middle-third rule states that if the eccentricity of the resultant vertical load stays within B/6 of the footing centerline (i.e., within the middle third of the footing width), the entire footing base remains in compression with no theoretical uplift. If the resultant falls outside the middle third, only part of the footing engages the soil, pressure concentrates sharply at the toe, and the footing may begin to rock or separate from the soil at the heel — a sign the geometry needs revision.
The most common fixes are: increase the base width (more vertical load from footing and heel soil, and a longer friction path), add a shear key projecting down from the footing to mobilize passive resistance, or improve drainage so soil moisture (and therefore friction loss) is controlled. Increasing the base width also generally helps the overturning and bearing checks at the same time.
No — it assumes the wall has a functioning drainage system (drainage aggregate, a footing drain, and weep holes) that prevents water buildup, consistent with standard retaining wall drainage design. Hydrostatic pressure from a clogged or missing drainage system can add 50–100% or more to the design lateral load and is a leading cause of real-world retaining wall failures, so drainage should never be an afterthought in an actual design.
The Retaining Wall Design for Civil Site Engineers article explains wall types, lateral earth pressure theory, and design considerations conceptually. This calculator is the numeric companion — plug in your own geometry and soil parameters to get actual factor-of-safety numbers for overturning, sliding, and bearing pressure.
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