Gabion & Rock Mattress Structures

Gabions and Rock Mattress structures have been marketed in Australia since the 1970’s. Internationally these products have been marketed for over a hundred years.

Gabions and Rock Mattress structures are generally formed by the weaving of wire (of varying diameter) into mesh which is then factory fabricated into box cages (of varying size) which are then site filled with stone to form dry-land structures such as retaining walls or in wet-land structures such as weirs or riverbank linings.

The wire that has been traditionally used in the manufacture of these gabion and mattress products supplied into Australia has been heavily galvanised and then may have extruded to the core wire a coating of PVC to provide additional protection. More recently there have been other coatings applied to the wire that purport to enhance the resistance of such wires to corrosion.

Gabions are box like units, generally of length either 2m or 4m and with a height of either 0.5m or 1m. Rock Mattress product is generally of larger plan area, typically 6m x 2m, but are much thinner in depth with typical dimensions ranging between 0.17m and 0.5m. All units are supplied folded flat to site and the customer must fabricate the supplied unit to size, join one unit to another to form the required structure, fill with suitable stone and complete the closure of the unit such that a stable structure is constructed. Gabions are ideal for use in retaining structures that have unfavourable foundation conditions. Gabions are quite flexible and can accommodate significant ground movement without catastrophic failure. Rock Mattress is an alternative to replace traditional rock armour treatments of structures against water erosion and scour. By encapsulating rock within a mesh layer, the effective shear capacity of such rock is increased providing additional protection against potential scour or erosive forces generated by water.

Retaining Solutions are highly experienced in the design and construction of structures using these products and can provide engineering advice, design and construction certification from project inception to completion.

Retaining Solutions promotes the use of gabions for retaining walls where foundation conditions are problematic. Rock Mattress is a very viable replacement option for large diameter rock armour works. The depth of Rock Mattress chosen will be a function of the expected shear forces being generated on the proposed structure. Gabions and Rock Mattress by their flexible nature generally do not require extensive foundation treatments prior to construction.

Gabions and Rock Mattress are stone filled on site and then dependent upon the design are joined one unit to the other to form a stable mass. The manufacturers of these products have very extensive instructions on the correct manner of constructing these products particularly with respect to lacing and filling techniques. Retaining Solutions is very experienced in such techniques and has the necessary labour and plant to successfully complete all projects using these products.

Thousands of gabion and mattress projects have been successfully completed throughout Australia in the last three decades. Like all engineering product, there are design and performance issues to be addressed. In applications where success has not been fully realised using these products, there have been simple detailing issues that may have been overlooked in the design process. The correct selection of coating process is not always considered. In any wet-land structure the designer is always advised to select the additional protection of PVC extruded to the wire rather than an uncoated wire notwithstanding that the basic wire may be heavily galvanised.

The correct selection and use of geotextiles (or filter layers) in all these structures is necessary, particularly when subject to hydraulic forces.

Gabion and rock mattress product is very versatile and when used in conjunction with well accepted design methodologies for these products and good construction practices will result in a long lasting, well performing engineering structure.

Gabion and mattress durability is a combination of the product supplied, the rock infill selected, the design process and the construction quality adopted.

The choice of gabion product selected should always be supported by well accepted product QC and QA documentation to well accepted international test methods and procedures. The quality of wire coating processes should be able to be substantiated by the supplier. The correct choice of wire coating process for the specific project environment is imperative.

ock quality should be defined in terms of minimum mechanical strengths consistent with the structure life. Suitable test methods exist locally to characterise rock quality. The physical characteristics of the rock infill should be defined both from a grading and shape perspective.

Construction quality will be helped by good design practice, careful selection of rock infill characteristics and the experience of the construction crew engaged to complete the works.

This form of construction has been gaining wider appeal in recent years from many architects based on the aesthetics of the product. Good visual appeal of the product and the satisfying “rock finish look” requires experienced installation crews with some

“hand packing” of front faces, careful selection of rock infill particularly with respect to the grading of such rock and the integration of additional soft landscaping features into the gabion structure. The use of tiered structures and planting is a common treatment.

he product easily accommodates curves, transitions and abrupt changes of direction. If required, the products may be cut on site to fit into existing structures. Gabion retaining walls may be constructed with a smooth or stepped front face. Gabion walls may include woven mesh reinforcement extending from the rear wall face into fill to create a soil reinforced structure significantly reducing the cost of traditional gravity gabion walls.

The integration of gabion retaining walls and protection from scour in a river training application is very easy with the incorporation of a rock mattress toe detail. Special units are available that allow filling at the front face with soils to provide a vegetated solution to slope stabilisation.