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| Wire Gabions |
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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:
TENSILE STRENGTH
JOINT STRENGTH / PULL-APART
RESISTANCE
SALT SPRAY
TESTS
PUNCH
TESTS
FLEXIBILITY
DIMENSIONAL
ACCURACY
PVC
COATING
INSTALLATION
TENSILE STRENGTH
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: |
| Criteria |
Test Method |
Grade |
Legend |
Red
Rust |
ASTM A610 |
10 |
< or =
0.01% |
White
Rust |
ASTM A610 |
3-G |
>10%
-
< or =16% |
Staining |
ASTM
A610 |
2 |
|
|
PUNCH
TESTS
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
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.
DIMENSIONAL
ACCURACY
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.
PVC COATING
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.
INSTALLATION
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. |
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