Edition 5Ideas and information for the clients of Concrib

The stepped gabion weir at Pacific Pines was built four and a half years ago by the Concrib team. The hydraulic energy dissipater was designed to cope with a 1 in 100 year flood - and that’s exactly what happened at the beginning of this year when freak flooding hit Queensland, leaving many demolished structures in its wake. However, due to the high quality of Concrib’s workmanship, and the fit for purpose design and materials, the gabion weir at Pacific Pines stayed strong and is now looking better than ever.

In this issueProject profile: Engineering withstands the elements at Pacific Pines.

Project profile: Concrib stabilises Griffith Road Bridge embankment

Engineered retaining walls: Maximising land values

Brisbane: (07) 3375 1800 Fax (07) 3375 1777Email concrib@ecn.net.au Web www.concrib.com.au

Building the stepped gabion weirThe project began in April 2007, and took just two weeks to complete. It was constructed from:

• StructuralearthfilltoLevel1compliance

• MaccaferriPVC-coatedwiregabions

• Non-wovengeotextile

• Hard,durablerock-fill100to150mmgrading

Engineering withstands the elements at Pacific Pines

Project profile

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The structure was built to create a water diversion by receiving overland flow and stormwater from a large area of southern Pacific Pines Estate.

The Concrib team faced a particular challenge with this project. Because of the stepped gabion design, the detailed earthworks of the structure dictated the accuracy of the finished gabion baskets. To overcome this, the engineers needed to achieve precise levels. They didthisbyemployingGPSpositioningand laser levels in conjunction with a special excavator with an extended boom, sometimes referred to as a ‘long-reach boom’.

A few years onJust a few years later, the stepped gabion weir and surrounding areas look very different to how they did originally. A variety of plants and shrubs have softened the appearance of the structure, giving

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the impression that it blends into the natural environment.

The life of the gabion weir is expected to be longer than the average human lifespan – about one hundred years. Longevitycan-andshould-berelateddirectly to the build quality of the gabions and the correct selection of durable rock-fill. To achieve this outcome, Concrib strictly complies with the gabion manufacturer’s comprehensive installation specifications to ensure straight, level and well-packed gabions.

GrantSigstonfromConcribsaid:“Forthe first few years after the structure was built, there wasn’t a large amount of rain. However, the unprecedented and prolonged wet weather of Dec 2010 to Jan 2011 put the gabion weir to the ultimate test, with massive one-in-100 year run-off and overland flow during this time. The structure suffered no damage from the floods, leaving us satisfied that we have achieved our objectives.”

Pacific Pines A few years on

Overview: Constructed in 1987, the embankment supporting Griffith Road has stood for many years.

It is believed that the material used to construct the embankment was excavated from the site of the adjacent marina, and in the long term this alluvial clay material has proved to be problematic. Three-tiered crib walls retained the original embankment, however these walls were not anchored or tied into the embankment in any way.

Wet weather caused problemsFollowing prolonged and unprecedented wet weather during 2010, the saturated embankment was showing signs of failure including lateral spread and bulging of the lowest tier crib wall. Geotechnical sampling, testing and analysis indicated that the global stability

Concrib stabilises Griffith Road Bridge embankment

Project profile

mmaxiiimiiisiiingg lland valuesmaximising land values

of the embankment was insufficient for it to remain intact due to the nature of the alluvial clays used in the construction in 1987. In fact, testing indicated the material had a friction angle of about 20 degrees and a bearing capacity of less than50kPa.

Remedial worksRemedial works to stabilise the embankment required the reconstruction of the three-tiered crib walls, however in this design the lowest wall was required to be supported on a piled foundation. As well as this, the poor clay material above the base of the lowest wall was excavated andreplacedwithCBR15material. The piles extended some eight metres deep to be founded in the underlying stiff clays. A sheet pile wall was driven above the top crib wall to support the roadway during reconstruction of the embankment and walls.

The contract let by the local authority detailed the design of the embankment and the piled foundation of the lower crib wall, with the actual wall structures being design and construct. The overall contract wasawardedtoAllenconPty.Ltd,withAllencon engaging Concrib to carry out the design, construction and certification of the crib wall structures.

Each wall is about seventy metres in length, with a total wall area of approx 270 square face metres.

Project: StabilisationofGriffithRoadBridgeembankmentadjacenttoNewportWaterwayMarina.CompletedAugust2011.

Client: Allencon

Engineered retaining wallsMaximising land values

Call us today to plan your next project. Brisbane: (07) 3375 1800 Fax (07) 3375 1777Email concrib@ecn.net.au Web www.concrib.com.au

Concrete crib walls

Rockcatch fencing

Concrete sleeper retaining walls

Patterned sleeper retaining walls

Gabion and rock mattress structures

Rockfall netting

Stone Strong

New directions

Segmental walls

FINALISTS in Category 1 of the prestigious CCF Earth Awards 2011 – celebrating “Excellence in Civil Construction.”