Enlarged Cotter Dam construction and schedule update

July 11, 2011

An undesirable geological feature in the base of the Enlarged Cotter Dam foundation has been uncovered which has delayed final preparations for the main dam wall. ACTEW has announced that this will impact the construction schedule and the estimated project completion date, but will not impact the project budget.

Geotechnical investigations undertaken during the planning phase for the Enlarged Cotter Dam identified the presence of a localised area of unsuitable material in the foundation, but the extent of this feature was not apparent.

The geological feature is a seam (or fault) between two monolithic rock segments, filled with weathered and unstable rock and clay. The feature runs parallel to the right hand abutment along the length of the dam and in some areas is up to nine meters below the foundation level. The fault also intersected with three other seams running at right angles to the abutments, forming a grid of excavation lines. Over 12,000 cubic meters of additional rock needed to be excavated.

As a result, work on the placement of roller compacted concrete (RCC) for the main dam has been delayed. Instead the team has been focussing on removing the unsuitable material to ensure the Enlarged Cotter Dam is founded on solid and stable rock, and filling the excavation with mass concrete to raise it to the foundation level required for the placement of RCC.

Work on the main dam wall is now expected to begin by August with the project now expected to be completed in June 2012.

View of the work in the foundation area for the Enlarged Cotter Dam   View of the foundation area for the Enlarged Cotter DamWork in the seam with the foundation   Enlarged Cotter Dam Work underway in the seam in the foundation