Thousands of years ago, Egyptians wove reeds into baskets; the baskets were filled with stones and buried along the Nile to control flooding and erosion. Later Europeans made stone-filled wicker baskets for both military fortifications and flood protection. These baskets acquired the name gabions, from the Italian word gabbione, meaning large cage. In the mid-nineteenth century, the first commercial gabion products were manufactured from woven or twisted mesh. The mid-twentieth century brought another change to the gabion with the advent of welding technology.
Over time, gabions have been improved and refined while retaining their most desirable and advantageous qualities. Each change reflects advancement in manufacturing and design resulting from the availability of new, better materials and techniques.
Welded wire mesh gabions offer the same flexibility as twisted mesh gabions with greater strength. Moreover, the superior coating technology used for Modular Gabion Systems offers greater corrosion resistance than can be achieved with twisted (woven) mesh.
When evaluating the benefits of welded mesh gabions, it is important to consider these points:
Independent laboratory testing confirms tensile strength values in excess of 3,000 pounds per lineal foot for standard 12 gauge welded wire mesh samples and values in excess of 3,700 pounds per lineal foot for standard 11 gauge welded wire mesh; these values exceed the requirements for welded mesh gabions as specified by ASTM-A974. Twisted mesh gabion manufacturers publish tensile strength values of 3,500 pounds per foot parallel to the twist and 1,800 pounds per foot perpendicular to the twist.
It is important to note that, unlike twisted (woven) mesh, welded wire mesh is symmetrical; the values are equal whether load is applied parallel to the line wires or perpendicular to the line wires. By contrast, twisted (woven) mesh offers significantly less tensile strength in the parallel axis when compared to welded mesh and half the strength in the perpendicular axis.
JOINT STRENGTH / PULL-APART RESISTANCE
The Oklahoma Department of Transportation conducted independent testing of all gabion connection methods and materials: spiral binders, Spenax and Tiger Tite hog rings and lacing wire. The OK DOT concluded that spiral binders, the standard connection for welded wire gabions, offer the greatest joint strength: 1,834 pounds per foot. Spiral binders are preformed in manufacturing which allows the use of heavier gauge wire than is used for lacing wire. Only spiral binders allow stress from opposing panels to be distributed evenly along the joint.
SALT SPRAY TESTS
ASTM A-974-97 for welded wire mesh gabions does not require salt spray testing, however Modular Gabion Systems welded mesh has been subjected to independent third party laboratory salt spray testing. Q-LAB Weather Research Service performed accelerated corrosion testing on 10 mesh panels; the results for each panel were identical:
< or =16%
Punch tests are referenced in ASTM A975-97 for twisted wire mesh gabions to preclude the manufacture of gabions from chain link meshes. However, punch tests are not representative of field conditions are not referenced in any current construction specification for gabions - twisted (woven) or welded - written by any agency.
Flexibility is a function of the gabion unit taken as a whole, rather than a function of the mesh alone. Full scale tests conducted by two independent agencies, (1) Selvage, Hebner, Nelson and Associates for CALTRANS and (2) R. L. Brockenbrough and Associates for PENN DOT concluded welded and twisted gabions, when fully assembled and properly filled, offer similar or equal deflection and flexibility.
Gabion baskets and mattresses assembled from welded wire mesh have a dimensional accuracy of better than 0.5 percent versus typical tolerances of plus/minus 5.0 percent for twisted mesh.
Twisted mesh gabions are coated by application of an extruded sleeve to the single strands of twisted (woven) wire. The coating is often stretched during manufacturing and may rupture in the twisting process. These residual stresses significantly reduce the UV tolerance and ability to protect the underlying wire from infiltration and migration of corrosive moisture along the wire under the coating. Wires at twisted joints rub against each other inside the coating when the mesh moves; this friction at the twisted joint causes abrasion damage and accelerates deterioration of the coating.
By contrast, the fuse bonded PVC powder coating of welded mesh gabions is bonded uniformly to mesh after welding to form a super skin. This prevents corrosive liquids from attacking the galvanized core wire - even in salt water. The fuse-bonding coating process eliminates residual stresses in the coating inherent in the extrusion process used by twisted mesh manufactures so the PVC retains its UV protection and prevents infiltration by water or other liquids and thus prevents any subsequent migration of those liquids along the core wire. The single wire strands of welded mesh cannot move at the joint so there is no internal wire abrasion to damage the coating.
Twisted mesh gabions must be supplied partially assembled. The baskets or mattresses require stretching to remove creases, kinks and to achieve full dimensional size. Twisted gabions are not self-supporting and are prone to significant slumping during the filling process.
Welded mesh gabions may be supplied in roll stock form, assembled, or partially assembled. Gabion baskets and mattresses meet dimensional specifications and proper shape without stretching or straightening; they are self supporting for easy assembly, placement and filling. Welded mesh gabions are assembled and joined with with quick-connecting, pre-formed spiral binders.
Choosing welded mesh gabion and its use often has more advantages as compared to woven mesh gabions