Gabion wall
A gabion retaining wall, per foot of wall: stacked courses of stone-filled baskets, optionally battered back, checked as a gravity wall on its base and at every joint between courses.
Inputs of the gabion wall #
- Gabion courses: the number of courses and their height, the base course width, the width step per course (each course narrower than the one below; one basket module is 1.5 ft) down to the narrowest width, and the stepped face: at the front (the backs flush, the usual arrangement) or at the back (the front flush). The batter angle tilts the whole wall back (about 6° is common); the base then dips toward the backfill. The gabion unit weight is γg = γs (1 − n) from the stone unit weight and the porosity of the fill.
- Backfill and soil: φ, the wall friction δ on the rough gabion back (2/3 φ to φ, the engineer's choice), the backfill slope, γ, a uniform surcharge (dead or live) and the soil depth in front for passive resistance.
- Stability and bearing: allowable bearing pressure, the base friction coefficient μ, the friction coefficient between courses and the allowable compressive stress in the gabions (the manufacturer's values), the passive reduction factor and neglected depth, the factors of safety and the eccentricity limit.
Auto-design (editor toolbar) varies the base course width (1.5-ft modules) and the width step per course; the number and height of the courses, the narrowest width, the face, the batter, the soil and the loads are kept. Objective: least gabion volume. Every other input is kept; see Auto-design.
Checks performed #
| Check | Basis |
|---|---|
| Earth pressure | Coulomb Ka(φ, δ, β, θ) on the plane through the heel of the bottom course and the back corner of the top course (θ negative for a battered wall), Pa = ½ Ka γ H² at H/3, the thrust at δ + θ below the horizontal; surcharge Ka q H cos θ / cos(θ − β) at H/2 |
| Sliding | Along the (inclined) base: (μN + Pp) / T ≥ FS, with N normal to the base and T along it |
| Overturning | About the toe ≥ FS |
| Bearing and eccentricity | Pressure along the base under D + H and D + H + L (ASCE 7-22 2.4.1) against the allowable; eccentricity within the entered limit |
| Joints between courses | For the courses above each joint (the earth pressure on the plane above it): sliding between the baskets, overturning about the joint's front edge, eccentricity and the compressive stress on the joint against the allowable; the worst joint of each check is reported |
The drawings show the wall section (the courses with their setbacks and batter, backfill, soil in front, surcharge, the horizontal earth pressure on the back plane, the main dimensions) and the service bearing pressure. The basket mesh, lacing, filter fabric and drainage are not part of the calculation.
Limitations #
- A drained backfill is assumed (no water pressure); seismic loads and global stability are not included.
- The steps of the back are replaced by the plane through the heel and the top back corner; the soil between the steps and that plane is not counted as weight (conservative).
- One course height for the whole wall; a custom arrangement of baskets is not offered.
Verification examples #
Verification status: 10 values compared in 2 examples (0 published, 2 hand calculations from the cited equations): 10 within tolerance, 0 recorded deviations. No published example: every value is a hand calculation. That checks the program against this reading of the code, not the reading itself. Code basis: written without the code document on hand, and confirmed only in part through published examples.
No free gabion design manual with a complete worked example could be retrieved (research/DOCUMENTS_NEEDED.md). Hand calculations in closed form (backend/tests/test_verify_gabion_wall.py):
| What it checks | Hand | ILX Calcs |
|---|---|---|
| Gabion unit weight 165 × (1 − 0.30) | 115.5 pcf | 115.5 |
| Two courses, no batter: sliding force / resistance ÷ 1.5 | 0.555 / 1.333 kip/ft | 0.555 / 1.333 |
| Overturning moment / resisting ÷ 2 | 1.110 / 6.096 kip-ft | 1.110 / 6.096 |
| Joint: sliding force / resistance ÷ 1.5 | 0.139 / 0.510 kip/ft | 0.139 / 0.510 |
| One course battered 6°: Coulomb Ka with θ = −6° | 0.2348 | 0.2348 |
| Force along the inclined base / resistance ÷ 1.5 | −0.100 / 0.845 kip/ft | −0.100 / 0.845 |