National Arboretum Canberra, Central Valley Earthworks

Project Location: Dairy Farmers Hill, Tuggeranong
Parkway Client: ACT Procurement Solutions
Client’s Representative: Brad Smith
Superintendent: Cardno Young Pty Ltd xx
Superintendent’s Representative: Stuart Oxborrow
Landscape Architect: Taylor, Cullity and Lethlean.
Project Start Date: May 2009

Description:

The Central Valley Earthworks project was to construct 36 earth terraces forming a central feature of the National Arboretum, Canberra.

Scope of works:

  • Clearing and grubbing of approximately 8 hectares.
  • Installation of environmental controls
  • Stripping and stock piling of approximately 15, 000 m3 of top soil
  • Earthworks requiring approx 32,000m³ of cut to fill
  • Excavation and subsequent filling of approximately 32,000 m3 of earth and rock.
  • Placement of the topsoil to the final levels and grades.
  • Grassing of completed profile approximately 8 hectares.

Discussion:

Guideline ACT came on board early in the project and was able to contribute engineering expertise to the discussions with the architects, so they fully understood the financial benefits of some modifications to their designs.

These early changes included the concept of balanced cut and fill and modifying the storm water controls, which meant eliminating buried storm water pipes and pits and replacing them with strategic earth contouring instead.

In order to fulfil the requirements of the design, the terraces were formed up and compacted as controlled fill. The fill material then had to be cut back to very specific design detail, requiring excessively high levels of grade checking and survey.

While the project was not technically difficult, it did require some specific manoeuvring by the excavators, such as ripping the terraces longitudinally before placing the top soil, and cutting the terraces to leave a high quality finish. On completion the terraces were seeded with grasses according to the design.

Immediately after the job was completed, there were several heavy rainfalls, but the terraces stood up well, testament to the quality of workmanship provided by Guideline ACT.

The terraces, now green with grass, are a grand earth staircase snaking down the side of Dairy Farmers Hill, providing a dramatic stage to overlook Lake Burley Griffin.