Constructing a massive wall with foundations in an underwater trench

Amrun Arraw Dam Project

The project

Bauxite mining requires a large source of water to wash the bauxite before it is transported to its destination. The Rio Tinto bauxite mine at Weipa, in far north Queensland, depends on a dam for its water. When the dam was found to be leaking, Keller was commissioned to stop the leak.

The challenge

This project had a number of challenges, most stemming from the scope of the project. Keller was required to build an 800m long cut-off wall, with foundations in the water, varying in depth from 10m in shallow water to 18m in deeper water. Cut-off walls are usually made from soil and bentonite or cement and bentonite, but these options posed both financial and availability challenges.

The solution

The construction process was two-fold: the digging of the trench, up to 18m deep; and the construction of the wall. Early stages of the trench digging revealed sections of ground were deeper than initially estimated, which had implications for the project schedule. To compensate, Keller ran two excavators – one 70-tonne, the other 90-tonne – consecutively, to keep the project on time. An 18-metre-reach arm sourced from Malaysia for the job proved invaluable.
In a bid to reduce costs but maintain structural stability, the project designer, KCB, suggested the wall be constructed from a consistent mix of soil, bentonite and cement, a process that had not been undertaken on such a scale on a project of this nature. It was Keller ‘s experience, knowledge and drive to undertake the work that largely contributed to Keller being commissioned for the project. Among the project efficiencies were the construction of a batching plant on-site, to mix cement and water, and the use of excavated soil in the construction mixture.

Project facts

Owner(s)

Rio Tinto

Keller business unit(s)

Keller Australia

Main contractor(s)

Rio Tinto Aican