Advantage:
Flexibility
Flexibility is an important benefit of any gabion structure. The double-twist hexagonal mesh construction permits it to tolerate differential settlement without fracture. This property is especially important when a structure is on unstable soil conditions or in areas where scour from wave action or currents can undermine the toe of the structure and cause structural settlement.
Durability
Gabions support plant growth which provides a live coating for the wire mesh and stones, adding to their durability. Generally, the wire mesh is needed for the first few years of the structure's life; later the void between the stones is filled with soil, silt, and plant roots which act as a bonding agent for the stones.
Strength
Steel wire hexagonal mesh has strength and flexibility to withstand forces generated by water and earth masses, and the pervious nature of the gabion allows it to absorb and dissipate much of that energy. This is evident on coast protection installations where gabion structures remain effective long after a massive rigid structure fails. Additionally, the double twisted hexagonal mesh won't unravel if cut.
Permeability
Gabion walls are pervious to water and stabilize slopes by the combined action of draining and retaining, precluding the development of hydrostatic pressure behind the gabion wall. Drainage is accomplished by gravity, as well as evaporation as the porous structure permits air circulation through it. As plant growth develops within the structure, the process of transpiration assists in removing moisture from the backfill - a much more efficient system than weep holes in standard masonry walls.
Low cost
Gabion systems are more economical than rigid or semi-rigid structures for the following reasons:
• It requires little maintenance
• Its installations does not require skilled labor and stone fill is available on site or from nearby quarries,
• It requires little or no foundation preparation, as the surface needs to be only reasonably level and smooth.
• Gabions are porous, requiring no costly drainage provision
Ecology
Gabions is an environmentally sensitive solution to slope stabilization. It has already been mentioned that stone fill is done with natural stones making the gabions, naturally porous allowing interaction between the land and the water table and also persuades deposition of soil in the smaller voids between the stone fill during drainage that again promote vegetation growth.
Aesthetics
Gabions supporting vegetation has already been discussed; in some case the vegetation growth is so intense, making the gabion structure invisible, and pleasant to look at. Again if additional effort is given during construction, the gabion can create really pleasing structure with or without vegetation. Unlike other types of materials such a modular block walls the gabion stones do not discolor due to drainage.
Specification:
All wire used in the fabrication of the gabion boxes and mattresses and in the wiring operations during construction shall have a tensile strength not less than 390 MPa and conform to BS 1052./1980.
Specification for mild steel wire for general engineering purposes.
Selvedges
All edges of the gabion boxes, mattresses, diaphragms and end panels shall be selvedged with a core wire diameter not less than 20% greater than that of the mesh wire. The selvedging shall be such that the mesh will not unravel and such that the strength of the connection between the selvedge wire and the mesh is equal to or greater than the breaking strength of the mesh.
Binding and connecting wire
The diameter of the wire core shall not be less than 2.2 mm for gabion boxes and 2.0 mm for mattresses.
Zinc Coating
All wire used in the fabrication of the gabion boxes and mattresses and in the wiring operations during construction shall be zinc coated to BS 10244-2 Steel wire and wire product zinc coatings. The minimum weight of the zinc coating shall be as follows:
DIAMETER OF WIRE(mm) |
WEIGHT OF COATING (g/sq m) |
3.90 & 4.40 |
290 |
3.00 & 3.40 |
275 |
2.40 & 2.70 |
260 |
2.00 & 2.20 |
240 |
Mesh
The mesh shall be hexagonal woven mesh with the joints formed by twisting each pair of wires through two full turns. The wire core diameter for gabion boxes shall not be less than 2.5 mm, and the wire core diameter for mattresses shall be not less than 2.0 mm. The nominal size of the mesh shall be 60 mm, being the distance between the axes of two adjacent twisted joints. The wire mesh shall have sufficient elasticity to permit elongation of the mesh equivalent to a minimum of 10% of the length of the section of mesh under test without reducing the diameter or tensile strength of the individual wires.
Properties of Mesh
STANDARD MESH-WIRE
Mesh Type 100X120 |
b |
Tolerance(mm) |
OD Wire ø(mm) |
Galvanized |
100 |
-4 +12 |
2,7 |
Galvanized + PVC |
100 |
-4 +12 |
3,7 |
Mesh Tolerance
The tolerance on the opening of mesh “b” being the distance between the axes of two consecutive twists.
PVC Coating
All wire used in the fabrication and wiring operations for the gabion boxes and mattresses shall have extruded onto it, after zinc coating, a coating of polyvinyl chloride (PVC). The coating shall have an average thickness of not less than 0.55 mm and nowhere shall be less than 0.40mm thickness. It shall be capable of resisting deleterious effects of natural water exposure and immersion in salt water and shall not show any material difference in its initial characteristics in accordance with the testing requirements specified.
PVC Coating Characteristics
The properties of the PVC material should adhere to the following:
Specific gravity |
1,30-1,35 kg/dm3, in accordance with ASTM D792 Table 1. |
Hardness |
Between 50 and 60 Shore D, according to ASTM D2240. |
Tensile strength |
Not less than 20,6 MPa, according to ASTM D412-92. |
Modulus of elasticity |
Not less than 18,6 MPa, in accordance with ASTM D412-92. |
Abrasion resistance |
The percentage of the weight loss shall be less than 12%, according to ASTM D1242-92. |
Creeping corrosion |
Maximum penetration of corrosion of the wire from a square cut end is 25 mm when the specimen has been immersed for 2,000 hrs in a 5% solution HCl (hydrochloric acid 12 Be). |
Tolerances
Wire diameter |
(BS 1052.80 IS 280-1978 &
NS 169-2045) +/- 2.5% |
Weight of gabions |
+/- 5% |
Mesh nominal size |
+/- 5% |
Dimensions |
|
Width |
+/- 5% |
Height |
+/- 5% |
Length |
+/- 3% |
The gabions are then tied together to form a gabion structure
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