2008 – Hinze Dam Stage 3 – development of the geological model and the implications for design

Chris Chamberlain, Don Macfarlane, Geoff Eades

Abstract: The Hinze Dam Stage 3 project is a significant upgrade of the existing 63.5 m high embankment dam, located on the Nerang River in the Hinterland of the Gold Coast in South East Queensland. Construction work commenced in early 2008 and is scheduled to be complete by the end of 2010.

Investigations at the dam have been undertaken in three stages since the early 1970’s for construction of the original dam and for each of the Stage 2 and Stage 3 raises. The Stage 3 investigation program began in November 2006 and was substantially complete by March 2008. The geology of the Hinze Dam foundation has been found to be more complex than had been previously determined, particularly with regard to the geological structure, variation in weathering profile and rock strength.

Development of the Stage 3 geological model of the foundation has been an iterative process utilising documented Stage 1 and Stage 2 data and new Stage 3 data. Much of the emphasis for the Stage 3 ground investigations has been placed on the right abutment ridge and saddle dam extension where most of the Stage 3 construction will take place. Here, the geological units comprise greywacke and deformed and variably silicified greenstone, phyllite and chert. Frequent review meetings were used to present each refinement of the geological model, challenge its geological credibility, identify uncertainties with the ground conditions and adjust the investigation program.

The paper describes the development of the Stage 3 geological model, provides an outline of the broader geology of the damsite and embankment foundation and also discusses how the complicated foundation geology has driven some of the engineering solutions that are currently being constructed at the dam.

Keywords: Hinze dam, geological model, foundation geology, design solution.