Client name: Leighton Contractors on behalf of Roads and Maritime Services

Duration: 2010 – present

Location: Woolgoolga, NSW, Australia


Coffey is helping to solve some of the most challenging issues in the projects of the Pacific Highway upgrade. 

Situation

This major upgrade project travels through the sensitive natural environment and difficult soft soils of the NSW north coast.

The $850 million Sapphire to Woolgoolga Pacific Highway upgrade extends from Sapphire to Arrawarra, bypassing the town of Woolgoolga. The project includes:

  • 25km of dual lane divided carriageways and 15km of local roads
  • 28 bridges – including new bridges and replacements
  • five new interchanges

With over two million cubic metres of earthworks, material management was a major challenge. All these materials needed to be processed to meet Roads and Maritime Services’ stringent performance specifications.

The centre pile of a three-pile group for a bridge abutment also caused major construction issues. The concrete pile needed to be 20m long. The depth and soil quality required pouring the concrete into a permanent casing to avoid soil slumping into the bored hole during construction. However, during installation, the bottom 9m of casing buckled, reducing the effective diameter of the pile at its base. Initial assessments suggested an additional 6m of pile was needed to achieve the required axial capacity — a costly and time consuming process.

Nearly 400,000m3 of excavated material wasn’t of suitable engineering quality for use in construction, and required low cost management of this surplus. Roads and Maritime Services agreed to place this material on a number of their owned sites within the project corridor. However, as Roads and Maritime Services may divest these sites in the future, they wanted assurance that the placed material wasn’t contaminated.

Solution

To reduce materials processing costs, we developed alternative material specifications—with similar performance profiles — in close consultation with Roads and Maritime Services. We also worked with the construction team and Roads and Maritime Services to develop alternative earthwork specifications that will provide a more cost-effective methodology — without compromising performance.

To address the centre pile construction issue, we considered the load carrying capacity of the pile group, as opposed to individual piles and proposed extending the lengths of the yet to be completed adjacent piles by 1.5m. This solution saved considerable cost and time, while achieving the required axial capacity of the pile group.

To help provide assurance that excavated materials weren’t contaminated, Leighton collected data on material movement and soil quality for the unsuitable material placed on Roads and Maritime Services land. On behalf of Leighton’s, we undertook an independent review of this data and assessed the quality of the material. During the review process, we identified enhanced ways of collecting and managing data to provide appropriate assurances. This information will assist Roads and Maritime Services in the future sale of surplus land, previously used for the management of excavated soils not suitable for engineering use.

Result

Management of surplus soils

The retention of soils on site represents the sustainable use of the resource, allowing rehabilitation of project borrow pits. This approach also resulted in significant savings in cost and time compared to alternative options such as offsite disposal to landfill, while not impairing the future value of the Roads and Maritime Services lands if divested.

Major cost and time savings

Our solutions delivered lower-cost, time-saving alternatives, while achieving the required performance.