Engineering geological roading aggregate investigations of the Wakatipu Basin

The Wakatipu Basin lies within the Otago Schist belt, and aggregates derived from the schist do not meet New Zealand basecourse specifications. This study comprises engineering geological investigations of the roading aggregate with the objective of identifying potential aggregate source areas which comply with specifications. Five aggregate sources, two glacial and three post-glacial, have been identified, and their geology related to aggregate quality. A survey of existing aggregate quarries confirmed the sub-specification quality of schist derived roading aggregate, and that the highest quality roading aggregate of the Basin is produced from exotic glacial transported graywacke. A graywacke rich aggregate source area of Kame terraces was investigated. Investigations included mapping at scales of 1:10 000 and 1:1 500, and the excavation of test pits. A geotechnical testing programme concluded that the Kame terrace source area was capable of producing roading aggregate for basecourse, and is comparable with the highest quality roading aggregate of the Wakatipu Basin. Subsequently, the Queenstown - Lakes District Council has developed an aggregate quarry within the Kame terrace source area