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ENVIRONMENT Tailings Management

Newcrest report into Cadia tailings dam failure released

cadia tailing dam failure aerial image
The Cadia Tailing Dam failure appears to have resulted from liquefaction of lower sedimentary layers

Newcrest has released a long-awaited technical report into the Cadia mine tailings dam failure in March 2018.

Newcrest appointed an Independent Technical Review Board (ITRB)to investigate the technical root cause of the tailings dam failure at its Cadia operation in New South Wales.

The ITRB comprised international experts and was chaired by Dr Norbert Morgenstern.

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Newcrest Managing Director and Chief Executive Officer, Sandeep Biswas, said: “We welcome the ITRB report which provides a great deal of technical insight which we will share with the industry. We accept all the findings and recommendations of the ITRB and will work with our stakeholders, including the NSW regulators, and continue the extensive drilling and geotechnical analysis of the foundations of the northern and southern tailings facilities which commenced following the slump.

We will continue to place the safety of our workforce and local community, together with care for the environment, at the forefront of our mind in operation of the southern tailings storage facility and as we progress work on the repair plans for the northern tailings storage facility.

We are targeting completion of a study on the repair plan in Q2 FY20.”

The ITRB report concluded that the dominant factor determining the location of the Cadia tailings dam failure was the existence of a low-density foundation layer in the vicinity of the slump.

Other factors that contributed were the local height of the dam, the prevailing phreatic conditions, and excavation at the toe of the structure in the area of the slump.

The low-density foundation layer material, which had not previously been identified, is relatively weak and highly compressible and brittle when subjected to significant load.

It was determined that the failure of this weak foundation material, when placed under load accumulated through the construction history, resulting in deformation of the wall.

This then triggered liquefaction of part of the tailings behind the embankment, causing it to slump forward.

The ITRB report noted that this material has to date only been found in close proximity to the area of the slump. Detailed seismic response analyses were conducted, with the ITRB concluding that the small seismic events which occurred the day prior to the slump did not contribute to the slump.

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