Gabion Installation Instructions
CDM regs state that retaining walls should be started 500mm below ground. The purpose of this is to allow for future excavations (see standard designs for more detailed explanation) and to get below the frost layer of 450mm. This also creates a toe in effect. Gabions have to be on a solid footing, all organic material needs to be removed that may decay. Best practice is for 100-200mm of type 1 to be compacted using a vibrating plate compactor. 100mm would be suitable for a 1m high wall, 200mm for a 3m high wall. The compacted hardcore can be treated as part of the basket and hence part of the toe in. In general this gives a toe in of 300mm. The standard designs are robust and it is not uncommon to see gabions installed at ground level for shorter walls. Without soil reports or a structural calculation a degree of common sense on site should be taken in respect to soil conditions, risk and appearance.
Baskets should be leant back at 6 degrees.
The Face of a gabion wall can be flush or stepped. On taller walls, it can be beneficial to step the baskets back to equalise the pressure between the heel and toe of the wall.
Gabions can be cut on site to the nearest full square, to achieve your required dimensions. Or we can cut them for you for an additional charge.
Health and Safety Regulations
Considerations in respect of health and safety are paramount in undertaking such works, to ensure that the construction can be undertaken with due regard for the health and safety for all concerned. In this regard, the requirements of The Construction (Design and Management) Regulations 2015(7.2) herein after referred to as CDM Regs. apply.
These Regulations also apply to domestic Clients.
There have been many incidences of both injuries and fatalities associated with the undertaking of construction works in conjunction with excavations. These have occurred where vertical or near vertical excavated faces have been provided and of which have either been unsupported or ineffectively supported and or where temporary unsupported excavated slopes or batters have been provided which are too steep to remain stable. The influence of other factors which could give rise to the potential for instability should also be included in considerations. These factors include but are not limited to water ingress, storage of materials, passage of vehicles.
The use of temporary propping to an excavated face in conjunction with earth retaining wall construction is generally not practical due to restrictions presented working.
The use of a temporary unsupported excavated slope or batter is typically employed and at a gradient of 45 degrees albeit subject to site conditions. This scenario is the basis of calculation of the standard designs where the gap behind the wall is filled with angular material.
Please ensure that all operators/Installers are wearing the correct PPP, this includes Safety Glasses, Safety Gloves, Steel Toe Cap Boots, a Hard Hat and a Hi Viz Top.
All gabions come flat packed. We attach all the panels together with stainless steel clips. The example above is a 2m x 1m x 1m.
There is also a partition in the middle of this basket, which is clipped in as well.
Using the lacing wire supplied, lace the corners of the baskets, tying the ends off with a pair of pliers. There is no need to lace the sides already clipped. Next, lace the formed baskets together, as shown with the blue lines on the diagram. There is an easier way if time is of the essence. You can purchase helicoils, which are long springs that you wind down the corners of the baskets. These springs attach the front and side panel of a basket and its adjacent panel in one go. They are a much faster way of assembling and attaching the baskets to each other and will substantially reduce your installation costs if using a contractor. You only need 2 springs per basket and 2 extra for the end of a run (in the case of 1m cubes). You don't need lacing wire for the sides when you use this method. The springs are more obvious than the lacing wire.
2.2mm Galfan lacing wire is supplied with the baskets (included in the cost). Helicoil springs are a faster way to install the basket, and can be used on the corners to join the baskets and attach them to the adjacent basket at the same time. We also supply preformed Galfan corner braces to further strengthen the fronts. 4 should be used per facing square metre. Or an alternative of a preformed windlass brace in 4mm wire.
When filling the baskets, it is necessary to insert a brace in the middle of the basket. This is important to stop the face bulging when filling. The higher the wall, the more important this is, as more force is exerted on the face. 1/3rd fill the basket and then create a windless, which are the red ties in the diagram to the left. Make a loop from the back to the front of the basket and join the ends with pliers. Put a sturdy flat stone in this loop and turn in circle, creating a tourniquet effect, which pulls the front tight. Fill on top of this, which will hold the stone in place. Repeat 2/3rds of the way up. Finally, lace the lids down with the lacing wire provided. Remember to attach all higher rows to the lower ones as well.
Choosing the correct stone fill is very important as gabions are a mass retaining system. The fill should be 100-200mm and angular. The quarried stone we offer is recommended as it is normally angular and comes with the best interlocking characteristics. We sell some stone types in bags that are rounded. These are for decorative purposes, and we would not recommend for walls where the baskets are stacked. If you wish to use a rounded stone, we would advise increasing the face thickness to 4 or 5mm to prevent deformation of the front. The stone should be laid flat and attention taken to avoid voids. The gabions can be machine filled, but again, attention must be taken to avoid voids by hand picking at regular intervals.
The Face of the gabion wall can be flush or Stepped. On taller walls, baskets are stepped back to equalize the pressure between the heel and toe of the wall. For the best finish, the fronts of the baskets should be fair faced by hand.
Gabions are normally machine filled in layers, the stone is picked to eliminate any voids. The faces are hand laid to give the appearance of a dry stone wall. This can be more easily achieved using the hand laying partitions option, which is an extra panel to make a narrow filling compartment at the front.
You can use a building rubble such as crushed concrete or brick at the rear of your basket, but this should be crushed to 100-200mm. Mobile Crushers can be hired for this purpose to be used on site.
The rock fill should be tightly packed, minimising voids. If possible, the fronts should be hand-packed. Using the lacing wire, all corners and the lid should be joined, making a continual seam. Bracing wire should be used to create a windlass 1/3 and 2/3rds up on a 1m high basket, and half way up on a .5m high basket. The baskets should be filled to a level where the lid bears down on the rock fill.
Rows should be laced to the row below them with lacing wire.
In rivers and in tidal waters, the permeability of a gabion wall is an advantage since water in the backfill during falling levels, can drain freely. The nature of the backfill may necessitate the use of a filter behind the wall, to prevent the leaching of fines. In cold climates, gabions are able to resist the action of frost heave. The life of a gabion wall is not necessarily limited by the effective life of the cage or basket, if the shape of the wall is such that the stone filling remains substantially stable after failure of the cage through corrosion or abrasion of the wire mesh.