Ensure an engineers report and any required permits are obtained for free standing walls and retaining walls prior to construction. Gabions, as mass gravity walls, generally require a base depth of no less than half the height. A variation to reduce the depth must include a permanent means of anchoring. Additionally the general rule of a gabion wall requiring a base of no less than half the height may or may not be sufficient.This requires expert advice. A modular gabion systems (MGS, Texas USA) design guide is provided here.
The work includes supply, construction of cages and installing rock.
a) Gabions shall consist of square or rectangular welded mesh constructed to form containers filled with rock. The gabions supplied to site shall conform to the following standards:
Gabions shall be constructed to a tolerance of +/- 5%.
a) Gabions shall be assembled and installed in accordance with dimensions as indicated here: Standard Sizes.
Wire for assembly, including stiffeners, spiral binders and C rings, shall be of the same material type as the gabion (Galfan, PVC, or Stainless Steel).
If C rings are used as fasteners, they shall be formed from wire and shall be a minimum of Al5% Zn 95%, galfan coated for galfan gabion and stainless steel for stainless steel gabion. The C rings must meet a minimum strength of 1700 N/mm2.
When PVC coated welded mesh gabions are specified, the galvanised wire shall be coated by fusion bonded PVC material.
C-Ring fasteners, if used over spirals, shall be formed from galfan wire. Test data must be provided to certify the fasteners provide the joint strength required. A minimum strength of 1700N/mm2. C Ring fasteners must have a minimum wire diameter of 3mm. When C Rings are used for PVC coated welded mesh the C Rings must be stainless steel and spirals must be PVC coated.
Rock shall conform to the quality requirements. Rock sizes for 75mm x 75mm welded gabion mesh shall be 80mm to 200mm. Rock sizes for 100mm x 50mm welded mesh gabion shall be 80mm to 200mm. At the discretion of the engineer recycled concrete rock, etc may used.
The foundation on which the gabions are to be placed shall be cut or filled and graded as required. Surface irregularities, loose material, vegetation, and all foreign matter shall be removed from foundation surface area. Gabions and bedding or specified geotextiles shall not be placed until the foundation preparation is completed, and the subgrade surfaces have been inspected and approved by the engineer or the engineer’s representative. Compaction of bedding or filter material will be required per plans and specifications. The surface of the finished material shall be to grade and free of mounds, dips or windrows. Extra care should be taken with foundation preparations in order to ensure a level and smooth surface. Geotextile shall be installed in accordance with the requirements of the plans and specifications.
The assembly and placement of gabions shall be in accordance with the following procedures:
Assembly. Rotate the gabion panels into position and join the vertical edges with fasteners for gabion assembly. Where spiral fasteners are used, crimp the ends to secure the spirals in place. Where C Rings are used for basket assembly, install the fasteners at a maximum spacing of 150 mm. Use the same fastening procedures to install interior diaphragms where they are required. Interior diaphragms will be required where any inside dimension exceeds 1m for gabion baskets. Diaphragms will be installed to assure that no open intervals are present that exceeds 1m.
Placement. Place the empty gabions on the foundation and interconnect the adjacent gabions along the top, bottom, and vertical edges using spirals. Spiral fasteners are commonly used for the assembly and interconnection of welded mesh gabions. Spirals are screwed down at the connecting edges then each end of the spiral is crimped to secure it in place.
Interconnect each layer of gabions to the underlying layer of gabions along the front, back, and sides. Stagger the vertical joints between the gabions of adjacent rows and layers by at least one-half of a cell length.
After adjacent empty wire gabion units are set to line and grade and common sides properly connected, they shall be placed in straight-line tension to gain a uniform alignment. Staking of the gabions may be done to maintain the established proper alignment prior to the placement of rock. No temporary stakes shall be placed through geotextile material. Connecting lacing wire and other fasteners (as allowed) shall be attached during the filling operation to preserve the strength and shape of the structure.
Internal connecting cross-tile (stiffener) wires shall be placed in each unrestrained gabion cell, including gabion cells left temporarily unrestrained. Two internal connecting wires shall be placed concurrently with rock placement, at each 300 mm interval of depth. In welded mesh gabions these cross ties or stiffeners will be placed across the corners of the gabions (at 300 mm from the corners) providing diagonal bracing. Lacing wire or preformed wire stiffeners may be used.
The gabions shall be carefully filled with rock, either by machine or hand methods, ensuring alignment, avoiding bulges, and providing a compact mass that minimizes voids. At no point in the filling process may rock be mechanically placed from a height of over 1m from machine to fill area. Machine placement will require supplementing with handwork to ensure the desired results. The cells in any row shall be filled in stages so that the depth of rock placed in any one cell does not exceed the depth of rock in any adjoining cell by more than 300 mm. Along the exposed faces, the outer layer of stone shall be carefully placed and arranged by hand to ensure a neat, compact placement with a uniform appearance.
The last layer of rock shall be uniformly levelled to the top edges of the gabions. Lids shall be placed over the rock filling using only approved lid closing tools as necessary. The use of crowbars or other single point leverage bars for lid closing is prohibited due to the potential for damage to the baskets.
The gabion lid shall then be secured to the sides, ends, and diaphragms with spiral binders, approved alternate fasteners, or lacing wire wrapped with alternating single and double half hitches in the mesh openings.
Any damage to the wire or coatings during assembly, placement and filling shall be repaired promptly in accordance with the manufacturer’s recommendations or replaced with undamaged gabion baskets.