Throsby Creek, Gungahlin

Project Overview

UEA’s Trenchless Division has successfully completed four 60 metre bores beneath Horse Park Drive in Gungahlin for Woden Contractors, in a mixture of hard clay and rock ground conditions. The works consisted of four number grade critical bores at four separate locations – one of the bores was in hard displaceable clay ground, one was in a hard shale ground and the remaining two bores were in hard rock ground.

Scope of Works

The proposed sewer pipe was a gravity main that connected into existing services and was required to be installed at 0.5% grade. UEA used a combination of the Guided Boring Machine and their laser guided Rock Case Boring Machine to complete the required on-grade pilot bores. The Auger Boring Machine was used to install the steel enveloper pipe.

Technical Details

UEA had to demonstrate the ability to deliver on grade bores in different ground conditions: hard clay, shale, and rock ground conditions. The team ensured that their methodology allowed for these changing ground conditions:

  • Bore 1 – Hard clay
  • Bore 2 – Hard clay changing to Class III shale
  • Bore 3 – Rock ground up to 40mpa
  • Bore 4 – Combination of Class III shale to rock

Pilot Bores

UEA used the Akkerman Guided Boring Machine to complete an on-grade pilot bore on bore 1. For bores 2,3 & 4 UEA used its in-house designed Rock Case Boring Machine (RCBM). The RCBM is highly suited for ground conditions from 4mpa to 40mpa as it guarantees grade accuracy similar to the GBM which is +/- 25mm for bores up to 120 metres in length.

Lead Case

When the pilot bores were complete, UEA used their conventional auger boring machine to install a steel encasing pipe which followed the pilot bores’ alignment on each of the four number bores.

Completion

The project was a success with UEA completing all bores on the correct grade and alignment, within five weeks of commencement.

Completed installation of the steel enveloper pipe in rock ground
Completed installation of the steel enveloper pipe in rock ground