Engineers involved in the investigation, design and construction of earthworks, especially where geosynthetic materials are involved, can learn from historical precedent – particularly when such structures have failed.

The case of the failure of the Gladstone Harbour bund wall has brought to light numerous recommendations for the future construction of such coastal earthworks, after an independent review into the wall was commissioned last year.

The Port of Gladstone Western Basin Strategic Dredging and Disposal Project (WBSDDP) allowed for a maximum of 46 million m³ of dredge spoil to be removed and disposed of, both offshore and within a constructed reclamation area.

The bund wall surrounding the reclamation area began leaking in August 2011 and coincided with mass deaths and disease of marine life in the nearby Great Barrier Reef World Heritage Area. In August 2013, engineers Bill Service and Warren Hornsey had made a presentation to Engineers Australia’s Gold Coast Regional Group titled Gladstone Harbour: Dredged Spoil Disposal Area Bund Wall - What went wrong? Their claims, that the geotextile fabric was of the wrong type and had been incorrectly fitted in the construction of the wall, were subsequently leaked to media outlets, prompting closer scrutiny.

In February 2014, federal environment minister Greg Hunt commissioned the Gladstone Bund Wall Independent Review panel to examine and report on information relevant to the design, construction and functioning of the outer bund wall of the WBSDDP and to consider the adequacy of monitoring requirements. The panel found that aspects of the design and construction of the bund wall were not consistent with industry best practice. Inadequate restraint of the geotextile liner, piping of water and sediment through paleochannels under the wall, and the erosion of mud outside the structure all contributed to changes in turbidity in the vicinity of the bund wall.

The Australian government approval of the WBSDDP reduced the footprint of the bund by 100 ha on the landward side of the reclamation area. This led to the proponent, Gladstone Ports Corporation (GPC), revising the design of the bund wall, which then impacted on how the wall functioned. The revised design changed the near-shore hydrodynamics and resulted in the mobilisation of additional sediment along the western side of the constructed bund wall, according to the report.

One of the key elements of the final design was the screening of the core rock to remove material of less than 12 mm diameter and the placement of a geotextile liner on the internal face of the bund wall.

For future construction of such bund walls in coastal areas, the report recommended that governments should require proponents to explicitly assess the risk of piping and to implement appropriate controls. Therefore, it was advised that geotextile materials designed to filter sediment should be:

• placed on the inner bund wall material and then be overlaid and secured by core material
• keyed into the rock armour material to prevent slippage and deformation from occurring prior to placement of the core material
• laid on the bund wall such that no wrinkles, gaps, folds or deformations occur in the material.

The review also recommended that GPC, its contractors and the Queensland and Australian governments should publish in the peer-reviewed literature the lessons from an engineering perspective on the construction of the bund wall to inform future design and impact assessment. There were many more findings and recommendations, particularly with regard to the inadequate monitoring of the bund walls’ performance after construction.