Gabion Wall Calculator

A gabion wall resists lateral earth pressure purely by its own mass, so the quantity that matters most is the effective unit weight of a rock-filled basket rather than any structural strength of the wire. Solid rock volume is the enclosed basket volume multiplied by one minus the void ratio. Hand-placed rock leaves 25 to 35 percent voids, so with a rock density of 2500 to 2700 kg/m3 for granite, basalt or limestone the wall behaves as a mass with an effective density near 1700 to 1900 kg/m3. Fill stone runs 100 to 200 mm, at least 1.5 times the mesh aperture so it cannot escape and no more than two thirds of the basket dimension so it can be placed. Stability is checked as for any gravity wall. The Rankine active coefficient Ka = tan^2(45 - phi/2) gives 0.333 for a backfill friction angle of 30 degrees, and the resulting thrust of 0.5 gamma H^2 Ka acts at one third of the height above the base. Overturning about the toe normally requires a factor of safety of at least 2.0 and sliding at least 1.5, with base friction commonly taken as about two thirds of the backfill friction angle. A practical rule is a base width of 50 to 70 percent of wall height, achieved partly by stepping courses back. Because the structure is free draining no hydrostatic term appears, a real advantage over solid walls. Surcharge, seismic action, bearing capacity and deep-seated slip are not covered, and walls above roughly 3 m warrant a geotechnical engineer.

The word comes from the Italian gabbione, an augmentative of gabbia meaning cage, and the object long predates civil engineering. Wicker baskets filled on site with earth and stone were standard equipment in siege warfare from the sixteenth century onward, used to build rapid parapets and to shield gun batteries, and they remained part of European fortification practice through the era of Vauban. The transition to a permanent civil product came with wire mesh. Officine Maccaferri of Bologna manufactured wire gabions used to repair the embankment of the Reno river at Casalecchio di Reno in 1893, and the double-twist hexagonal mesh developed for that market proved decisive, because a broken wire in a double-twist fabric does not unravel the way welded or single-twist mesh can. Durability then became a coatings problem, progressing from plain galvanizing to heavy zinc coatings, to zinc-aluminium alloy, and to PVC over a galvanized core for aggressive or marine exposure. The products are now covered by standards including EN 10223-3 for the mesh and EN 10244 for the coatings in Europe and ASTM A975 in the United States, with agencies such as the FHWA publishing design guidance for walls and mattresses. The military lineage never disappeared either: the collapsible fabric-lined wire cage used for modern field fortification is a direct descendant of the original earth-filled basket.