Design and Installation of Gabion Structures

 Design and Installation of Gabion Structures

A Gabion structure :-  Pre-assembled Structure Prepared from rectangular cages made of mechanically woven double twisted hexagonal mesh filled with rock or stones.

Gabion” or “Cage wall

    “Gabion” or “Cage wall” is designed especially for erosion control, involves stacking stones and rocks on top of the other, and using steel and geo-fabric to tie the structure together for added strength.

IRC Guidelines:- IRC Guidelines for Design and installation of Gabion structures are given in IRC SP :116-2018

Typical Gabion Structures with different components

     It is a simple gravity retaining structure, which retains soil with its weight. These types of structures are in use in highways, bridges, canal linings, buildings, shore protection works, etc.

    The porosity of gabions prevents the pore-water pressure development behind the walls which, is one of the major advantages of these kinds of systems. These structures blend with the surroundings and allow vegetation to take roots through the structure which enhances the life of the structure. Reduced carbon foot prints are also a noticeable feature when compared to conventional solutions.

    As there are avenues for the water to easily pass through, there is very little chance of the wall breaking away, causing landslips and affecting the integrity of the road itself,

Components of Gabion retaining wall

Gabion walls are mass gravity walls having three major components like 

1) Gabion box, 

Gabion Box is made of Mechanically Woven, Double-Twisted Hexagonal Wire Mesh Gabions, the mesh image as shown below

A) Technical Specification of Gabion / rivet Mattress Mesh

1) A terminal wire is used to edge the wire mesh perpendicular to the double twist by mechanically wrapping the mesh wires around it at least 2.5 times (Fig. 2a).

2) The hexagonal shape of the mesh helps in achieving uniform distribution of forces. Mesh should be non-corrosive and should possess high tensile strength.

3) All tests on the mesh, lacing wire and selvedge wire (Fig. 2a) must be performed prior to manufacturing the mesh. 

4) Tensile strength: The wire used for the manufacture of Mesh shall have a tensile strength minimum 350 N/mm2 – 550 N/mm2 in accordance with IS 280. Wire tolerances shall be in accordance with IS 16014 (Class T1). 

5) Elongation: Elongation of wire shall not be less than 10%. Test must be carried out on a sample at least 20 cm long.

6) Metallic coating: The wire shall have minimum quantities of metallic coating given in accordance with IS 4826 and Zn Al alloy coating.

B) Stone for filling gabion 

1) An unweathered (sound) naturally occurring angular or crushed hard rock material can be used for filling. 

2) Stone for the Gabion facia shall be hard, angular to round, durable and of such quality that they shall not disintegrate on exposure to water or weathering during the life of the structure. 

3) The minimum size of the rock to be filled in the boxes is governed by the mesh opening “D” in the mesh.

4) The minimum and maximum size of the stone used for filling shall be 1.5 to 2.5 times the mesh opening. 

5) Each range of sizes may allow for a variation of 5% oversize rock by number of particles, or 5% undersize rock by number of particles, or both. 

6) The rock pieces should be properly hand-placed and packed with their larger dimensions in the horizontal position.

7) The size of any oversize rock shall allow for the placement of minimum of three layers of rock must be achieved when filling the 1 m high units and a minimum of two layers for the 0.50 m high gabion units and 0.3m thick gabion mattress.

C) Filter media and backfill

1) Filter media shall be non-woven needle punched or thermally bonded geotextile. The geotextile shall be made of Polyester or Polypropylene. The mean values of geotextile specification shall be as per Table 7, 8, 10 and 11 of IRC SP:116-2018.

D) Foundation and Backfill soil properties

The value of cohesion ‘c’ and angle of internal friction ‘Φ’ vary for different backfill and foundation materials. These values shall be determined by carrying out tests in laboratory. In case of absence of the soil properties, values given in IS 14458-Part 2 may be used.