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