Foundations for a clarifier at the Te Maunga Wastewater treatment plant; design and construction

C. Santamaria, H. Wahab, F. Bruce & S. Edmonds
Beca Limited, New Zealand

ABSTRACT

The Te Maunga Wastewater Treatment Plant required the design and construction of a new clarifier as part of the Tauranga City Council plan to provide a resilient treatment process path. This required that some of the site geohazards, such as liquefaction and associated lateral spread, be well understood for the foundation design. Therefore, the ground investigations and assessments aimed to reduce the uncertainty around the depth and extent of liquefiable layers. Once the geotechnical assessments were completed, an optioneering process followed in conjunction with early contractor involvement, to assess several options for foundations and ground improvement options. The outcome resulted in the selection of driven piles for the
clarifier foundation. The pile type chosen consisted of an open-ended steel casing with a bottom driven concrete plug, and subsequent installation of reinforcement and concreting inside of the casing. As part of the design process, a site trial was undertaken to understand the construction risks and to gather information about pile capacity. During construction, the design assumptions were confirmed, and acceptance criteria were established by means of dynamic testing and a static load test.