Small centralisers, big rewards

When using soil nails to reinforce and stabilise existing ground, the quality of materials, installation and grouting are key to ensuring the project is successful. Although they may be small, centralisers play an important role in such installations to ensure the soil nail remains centred and even grouting is achieved.

Soil nailing is a remedial construction technique used to stabilise natural soil slopes, generally by installing steel bars into the ground. It is commonly used in areas with limited access or difficult ground conditions that prevents piles from being installed, or where existing slopes, excavations and retaining walls are showing signs of failure.

Even grouting to provide support

Soil nails can be installed using a variety of methods, but when they are installed into pre-drilled holes, they need to be grouted into place. The key to grouting is ensuring it is even and the soil nail remains centred in order for its full load bearing capacity to be realised.

Jason Linaker, Managing Director at kwik-ZIP, said centralisers are one of the tools available to assist in this process.

“The primary function of centralisers is to keep the soil nail centred in the borehole,” Mr Linaker said.

“By ensuring the soil nail stays centred, centralisers such as the kwik-ZIP GT series allow contractors to achieve consistent and adequate grouting which is imperative for the long-term success of an installation. Centralisers protect the soil nail from corrosion by sealing it from environmental elements such as moisture and acidic soils.

“While the bows of some centralisers can make it hard to correctly grout soil nails, the GT series has been designed so that they do not impact the ability of the grout to encase the soil nail due to gaps between each bow.”

Grouting also provides a great deal of protection from corrosion by sealing the soil nail from elements such as moisture.

Corrosion protection

The GT series centralisers are made with a high grade thermoplastic called ACETAL POM so they are strong and corrosive-free, making them ideal for soil nail installations.

“Centralisers manufactured with fully inert material with no metal parts removes the potential for corrosion when compared with metallic centralisers,” Mr Linaker said.

“This is an important consideration in areas with acidic soil which would cause metallic centralisers to corrode.

“This is a big problem as corrosion of metallic centralisers can result in voids in the grout allowing moisture egress to the soil nail thus increasing corrosion activities.

“For projects using steel soil nails, corrosion of metallic spacers can also transfer to the soil nail and affect the overall integrity of the installation.”

Easy use and Australian designed

Mr Linaker said the GT series has been designed with a simple integrated locking mechanism to allow for rapid installation, which means no fiddly or labour intensive processes which can hold up construction.

“They are also Australian designed and warehoused locally so there are no long lead times and, combined with their segmented design, allow for compact packing and thus lower freight costs.”

The GT series fit a range of bar and pipe diameters from 18mm (0.70”) OD to 65mm (2.56”) OD, and have four bow heights ranging from 10mm (0.78”) to 40mm (1.57”), so they are suitable for a wide range of ID-OD combinations.