ACETex for Ground Improvement at Brisbane’s Airport Link

The project

Brisbane’s continued growth in recent times has seen the need to undertake major infrastructure works to improve the flow of traffic around the city. In 2008, the Queensland Government appointed a contractor to commence Australia’s largest infrastructure project, worth $4.8 billion.

The works comprise three main sections - the Northern Busway, Airport Link and the Airport Roundabout Upgrade. The Airport Link is a 6.7km toll road passing through the inner north suburbs of Wooloowin, Kedron, Toombul and Hendra before meeting with the Airport Roundabout Upgrade works.

Much of the road was to be constructed through low lying relatively soft ground requiring ground improvement to accommodate the works.

How Global Synthetics supported this project

Global Synthetics has supplied many thousands of square metres of Geosynthetics to aid in ground improvement at the site.

ProFab nonwoven geotextiles have been used for separation under embankment fill, Secugrid biaxial geogrids for reinforcement of working platforms and access roads and ACETex structural reinforcement geotextiles for the Load Transfer Mats (LTM ).

Many of the road sections parallel with the existing East-West Arterial Road required elevated embankments and flyovers to cross existing roadways. The rigid abutments around flyovers and elevated roadways were founded on Controlled Modulus Columns (CMC®).

Where the piled sections of roadways transitioned to traditional, more flexible earth filled embankments, the design called for an LTM to more evenly distribute imposed loads, reduce lateral loads on outer piles, eliminate the need for pile caps and minimise differential settlements.

The LTM sits over the CMC piles and consists of a granular blanket reinforced in two directions (longitudinal and transverse in relation to the roadway alignment) by a high strength structural ACETex reinforcement geotextile.

Each layer of geotextile is separated by a 300mm granular layer. The specification for the reinforcement geotextile within the LTM was for a working strength of 180kN/m @ 5% total strain, limited to 2% creep strain at a 120-year design life. ACETex GT500 woven polyester reinforcement geotextile was proposed and selected for use as it satisfied all of the technical requirements of the specification and provided a commercially attractive solution.

Engineering support for the best long term result

An isochronous stress-strain relationship curve is required (introducing a time variable relationship between load and strain) when assessing high strength reinforcement geotextiles to determine the available stress at the nominated level of strain and time.

Ignoring the strain/time relationship can lead to an underestimation of product strength being offered against the specification. The ACETex GT500 is produced with an ultimate tensile strength of 500kN/m at an ultimate total strain of 10%, but with very high resistance to creep strain effects over long periods. The reinforcement geotextile selection process highlighted the limited understanding of the technical specification performance requirements, even by competing suppliers of such material.

Global Synthetics was believed to be the only geotextile supply company to understand the specification and offer a product that met the technical requirements of the Specification.

Get advice and support on technical reinforcement applications

Global Synthetics has proudly supported the delivery of the Airport Link Project. The use of an LTM reinforced with ACETex reinforcement structural geotextile over CMC piles is a relatively new ground improvement technique in construction over soft ground conditions and has been successfully applied in the Airport Link Project.