Retaining Wall Stability Calculator

Check sliding, overturning and bearing capacity factors of safety for gravity and cantilever retaining walls using Rankine or Coulomb active earth pressure.

Structural Engineering Preliminary design Educational use only

Retaining Wall Stability Check

Geometry & Materials

Set to 0 for granular backfill (common for active earth pressure).

Loading & Design Settings

β = 0° for level backfill.

Use 0° for Rankine; typical δ ≈ 0.67φ for Coulomb.

Typical μ ≈ 0.5–0.6 for concrete on granular soil.

Results

Sliding –

FSslide = Resisting / Driving

–

Overturning –

FSOT = ΣMresist / ΣMoverturn

–

Bearing –

FSbearing = qallow / qmax

–

Earth Pressure & Resultant

Active coefficient Ka

–

Active force Pa (kN/m)

–

Resultant location from base (m)

–

Detailed forces and moments

Vertical forces (kN/m)

  • Self-weight of stem: –
  • Self-weight of base: –
  • Soil over heel: –
  • Surcharge over heel: –
  • Total vertical V: –

Moments about toe (kN·m/m)

  • Resisting moments ΣMR: –
  • Overturning moments ΣMOT: –
  • Resultant eccentricity e: – m
  • Maximum bearing pressure qmax: – kPa

This tool assumes a straight cantilever/gravity wall with level base, drained granular backfill (unless cohesion is entered), and no water pressure. Use for preliminary checks only.

How this retaining wall stability calculator works

This calculator performs a classical external stability check for a cantilever or gravity retaining wall. It evaluates:

  • Sliding stability along the base
  • Overturning stability about the toe
  • Bearing capacity and eccentricity at the foundation level

1. Active earth pressure

For a wall of height \(H\) retaining soil with unit weight \(\gamma\), friction angle \(\phi\), cohesion \(c\), and uniform surcharge \(q\), the active earth pressure coefficient \(K_a\) is:

Rankine (level backfill, vertical wall, no wall friction)
\(K_a = \tan^2\left(45^\circ - \dfrac{\phi}{2}\right)\)

The active earth force per unit length of wall is then:

\(P_a = \dfrac{1}{2} K_a \gamma H^2 + K_a q H - 2 c \sqrt{K_a} \, H\)

The resultant from the triangular component acts at \(H/3\) above the base; the surcharge component acts at mid-height \(H/2\). For simplicity, this tool combines them into an equivalent resultant at an effective height close to \(H/3\).

2. Vertical forces and stabilizing moments

The calculator models the wall as a rectangular stem and base slab and includes:

  • Self-weight of the stem: \(W_s = \gamma_c \, t_s \, H\)
  • Self-weight of the base slab: \(W_b = \gamma_c \, B \, t_b\) (with an assumed base thickness)
  • Weight of soil over the heel: \(W_{soil} = \gamma \, b_h \, H\)
  • Equivalent vertical load from surcharge over the heel: \(W_q = q \, b_h\)

Each weight is applied at its centroid, and its lever arm to the toe is used to compute resisting moment \(\Sigma M_R\).

3. Sliding check

Sliding is checked by comparing the available frictional resistance along the base to the horizontal driving force from earth pressure:

\(F_{slide} = \mu \, V\)
\(FS_{slide} = \dfrac{F_{slide}}{P_a}\)

where \(V\) is the sum of vertical forces and \(\mu\) is the base friction coefficient.

4. Overturning check

Overturning is evaluated about the toe. The factor of safety is:

\(FS_{OT} = \dfrac{\Sigma M_R}{\Sigma M_{OT}}\)

where \(\Sigma M_R\) are stabilizing moments from vertical loads and \(\Sigma M_{OT}\) are overturning moments from earth pressure.

5. Bearing pressure and eccentricity

The resultant of all forces is located at an eccentricity \(e\) from the center of the base:

\(e = \dfrac{B}{2} - \dfrac{\Sigma M_R - \Sigma M_{OT}}{V}\)

Assuming linear bearing pressure distribution and no tension, the maximum and minimum pressures are:

\(q_{max} = \dfrac{V}{B} \left(1 + \dfrac{6e}{B}\right)\)
\(q_{min} = \dfrac{V}{B} \left(1 - \dfrac{6e}{B}\right)\)

The factor of safety against bearing capacity failure is:

\(FS_{bearing} = \dfrac{q_{allow}}{q_{max}}\)

Typical target factors of safety

Actual values must follow the governing code (e.g., AASHTO, Eurocode, local bridge manuals) and project specifications. Common preliminary targets for permanent walls are:

  • Sliding: FS ≥ 1.5
  • Overturning: FS ≥ 2.0
  • Bearing capacity: FS ≥ 3.0 (against ultimate capacity)

Limitations and assumptions

  • Plane-strain, straight wall with uniform soil conditions.
  • No hydrostatic or seepage water pressures are included.
  • Backfill is homogeneous and isotropic; wall is rigid.
  • Internal stability of reinforced soil (e.g., geogrids) is not checked.
  • Global stability (slip circles, compound failure) is not evaluated.

Use this tool for education, quick checks, and early-stage sizing. Final designs must be performed and reviewed by qualified geotechnical and structural engineers with project-specific investigations.

Frequently asked questions

Can I use cohesive backfill in the calculator?

You can enter a cohesion value, and the Rankine equation will reduce active pressure accordingly. However, relying on cohesion for long-term retaining wall stability is generally discouraged because cohesion can degrade over time. Many design manuals recommend using \(c = 0\) for active pressure.

How do I account for water pressure?

This version does not explicitly include hydrostatic pressure. For saturated conditions, you should:

  • Use effective unit weights for soil (submerged γ).
  • Add a separate triangular water pressure distribution on the wall.
  • Consider drainage measures (weep holes, drains, backfill filters).

What if my wall has a key or battered stem?

Keys and stem batter can significantly improve sliding and overturning resistance. This simplified model does not include them explicitly. For more advanced geometries, use this calculator as a starting point, then refine the design with more detailed software or hand calculations.