Geogrid raft foundation ideal for seismic protection


The use of a Geogrid reinforced aggregate raft foundation is a well-known and respected method of ground improvement in seismic events, and has been identified by the Department of Building and Housing as one of the suggested methods for use in TC3 areas.

This method is currently used by engineers in the Christchurch rebuild and many other locations around New Zealand in residential and commercial applications.

Cirtex offers Geogrids for TC2 and TC3 foundations with added benefits for the design engineer.

The series of earthquakes in Christchurch has once again proved the benefit of Geogrid reinforced structures in seismic engineering. The combination of a SecuGrid Geogrid with higher tensile modulus (stiffness) and a granular material provides a composite mechanically-reinforced foundation layer.

The TC2 and TC3 guidance document recognises the Geogrid reinforced raft foundation as an option available to the design engineer, and gives guidance for the use of Geogrids in foundation applications.

Triaxial or radial stiffness can be described as the tensile modulus of the Geogrid in three or more directions or, more importantly, at its weakest point. Cirtex offers the SecuGrid range of Geogrids where triaxial or radial stiffness is required, which demonstrate excellent radial stiffness, in most cases significantly better than other options.

In addition to proven and documented bearing capacity improvement and composite mechanically-stabilising performance, SecuGrid offers the added benefit of high strength at low elongation, and can therefore be considered for resisting lateral spread, a key function for some sites.

This removes the requirement for multiple grid types on one site, and time-consuming cross layering of narrow uniaxial grids.

SecuGrid is very easy to install due to its low memory (recoil effect), and because it comes in 4.75m wide rolls, reducing on-site wastage and overlap.

Cirtex is able to assist in many Geosynthetic applications, including reinforced soil walls, pavements and embankments, subsoil drainage filtration, slope stability, earth anchoring, landfill and environmental barrier systems, stormwater management systems, erosion and sediment control, coastal protection, surfacing reinforcement, dewatering and landscape edging.

Contact Cirtex to discuss any Geosynthetic challenges you may have on 0800 247 839 or visit

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