Gabion Wall Design Calculator
Conceptually size a gravity gabion retaining wall and check sliding, overturning, and bearing capacity safety factors. Supports metric and US customary units.
Geometry & Soil
Loads & Bearing
How this gabion wall design calculator works
This tool models a straight gravity gabion retaining wall with level backfill. It estimates the wall weight from the geometry and gabion unit weight, computes active earth pressure using Rankine theory, and checks:
- Sliding stability along the base
- Overturning about the toe
- Bearing pressure and eccentricity at the foundation
Key assumptions
- Level backfill surface and no water pressure (drained conditions).
- Homogeneous granular backfill with friction angle φ.
- Rigid, prismatic wall with linear batter faces.
- No seismic loads or live loads other than uniform surcharge q.
Design formulas used
1. Active earth pressure (Rankine)
Active earth pressure coefficient:
\[ K_a = \tan^2\left(45^\circ - \frac{\varphi}{2}\right) \]
Resultant active thrust on the wall (including surcharge):
\[ P_a = \frac{1}{2}\,\gamma_{\text{soil}}\,K_a\,H^2 + q\,K_a\,H \]
It acts at H/3 above the base.
2. Wall weight and centroid
The wall cross-section is approximated as a trapezoid with base width \(B\), top width \(b_t\) and height \(H\).
Top width:
\[ b_t = B - (\text{front batter} + \text{back batter}) \]
Area per meter length:
\[ A = \frac{(B + b_t)}{2}\,H \]
Wall weight per meter:
\[ W = \gamma_{\text{gabion}} \, A \]
3. Sliding check
Resisting force:
\[ R = \mu \, W \]
Driving force:
\[ D = P_a \]
Factor of safety against sliding:
\[ FS_{\text{sliding}} = \frac{R}{D} \]
4. Overturning check
Overturning moment about toe:
\[ M_o = P_a \cdot \frac{H}{3} \]
Resisting moment about toe (from wall weight):
\[ M_r = W \cdot x_W \]
where \(x_W\) is the horizontal distance from toe to the centroid of the trapezoid.
Factor of safety against overturning:
\[ FS_{\text{overturning}} = \frac{M_r}{M_o} \]
5. Bearing pressure and eccentricity
Resultant location from toe:
\[ x_R = \frac{M_r - M_o}{W} \]
Eccentricity from center of base:
\[ e = \frac{B}{2} - x_R \]
Assuming linear pressure distribution:
\[ q_{\max} = \frac{W}{B}\left(1 + \frac{6e}{B}\right), \quad q_{\min} = \frac{W}{B}\left(1 - \frac{6e}{B}\right) \]
Factor of safety for bearing:
\[ FS_{\text{bearing}} = \frac{q_{\text{allow}}}{q_{\max}} \]
Interpreting the results
- FS >= required: shown as “OK” in green.
- FS slightly below required: shown as “Low” in amber – consider increasing base width or wall height steps.
- FS well below required: shown as “Fail” in red – redesign is needed.
Typical ways to improve stability
- Increase base width (add another gabion basket at the heel).
- Use heavier rock fill (higher γgabion).
- Improve foundation soil or increase footing width to reduce bearing pressure.
- Provide drainage to reduce pore water pressure behind the wall.
Frequently asked questions
Can I use this for tiered or curved gabion walls?
The calculator assumes a single straight wall. For stepped or terraced walls, you can approximate each tier separately, but a full 2D or 3D analysis is recommended for complex geometries.
What about seismic design?
Seismic earth pressures and inertia forces are not included. If your project is in a seismic region, use an appropriate code-based method (e.g., Mononobe–Okabe) and consult a structural/geotechnical engineer.
What basket sizes are commonly used?
Many suppliers offer standard gabion baskets such as 1.0 m × 1.0 m × 2.0 m or 0.5 m × 1.0 m × 2.0 m. The suggested layout in this tool is conceptual; always coordinate final dimensions with the manufacturer’s catalog and detailing requirements.