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AuthorTensar International Ltd

DateJul 10 2018

How Tensar’s TriAx geogrid works

Creating a mechanically stabilised layer

If you’re using a mobile crane, piling rig or other heavy plant on a construction site—particularly where the ground is weak or unstable—having a safe working platform is vital.

Tensar’s TriAx geogrid stabilises granular working platforms by creating a ‘mechanically stabilised layer’.

Tensar TriAx geogrid stabilises granular working platform

  1. A layer of aggregate (granular fill) is placed over a TriAx geogrid
  2. The aggregate and the geogrid interlock, forming a confinement effect
  3. This confinement is what stabilises the aggregate

Having a mechanically stabilised layer increases the working platform’s bearing capacity while drastically reducing the amount of aggregate that needs to be used.

This has the benefit of allowing cranes or piling rigs to carry much heavier static loads.

The confinement effect

tensar confinement

Ground stabilisation relies on the interlocking mechanism between the aggregate and the TriAx geogrid, where a load placed on the aggregate causes it to becomes compacted and confined.

This confinement effect—where the aggregate catches in the apertures of the geogrid and pushes up against its ribs—prevents the layer of aggregate from moving laterally (sideways).

For a demonstration of how confinement works, watch the video below.

The triangular rack represents the apertures of the TriAx geogrid and the tennis balls act as the aggregate.

When it comes to using geogrids to stabilise working platforms, Tensar’s current approach is either to:

The BRE’s review of BR470 confirms that alternative design methods can be adopted provided that:

  • the objective of safety is preserved
  • the alternative approach is based on “credible and representative research”

Credible and representative research

Tensar’s extensive programme of research dates back more than 30 years and demonstrates in detail the benefits of incorporating geogrids such as TriAx into working platforms.

The most recent research was conducted at the facilities of the BRE in 2007 and 2010. This determined the effects of a mechanically stabilised layer incorporating the TriAx geogrid on the bearing capacity of a well-graded granular fill placed over weak subgrade soils.

Tests found that the TriAx geogrid could increase bearing capacity of the granular layer by more than a factor of two.

Benefits of using Tensar geogrids in working platforms

  • Financial savings that result from using less aggregate (typically up to 50% less in many cases)
  • Projects can be completed in much less time
  • Environmental benefits that come with using less carbon (i.e. in aggregate)
  • Higher bearing capacity
  • Better general access to construction sites
  • Less deformation to working surfaces
  • Can be deployed in all ground conditions

Working platform case study—Stoke Quay, Ipswich

To illustrate the potential value of using Tensar’s approach, in 2012 Tensar was enlisted to design a working platform for a tracked piling rig used in the construction of a new apartment block and townhouse development in Ipswich. You can read more about this case study here.

Using the TriAx geogrid to build a mechanically stabilised layer as an alternative to the client’s original design for its working platform (which was based on the guidance in BR470) meant:

  • a reduction in aggregate of over 800mm
  • a cost saving of £15.20 per m2 of platform
  • an overall saving for the project of £250,000
geosynthetic reinforcement