THROSBY CREEK SEWER INSTALLATION, GUNGAHLIN

Project Overview

UEA was contracted to bore and install 240 metres (four 60 metre bores) of DN225 UPVC sewer pipe within a steel enveloper beneath Horse Park Drive in Gungahlin for Woden Contractors, in a mixture of hard clay and rock ground conditions. The works consisted of four 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.

Location

Gungahlin NSW

Geology

Hard clay and rock

Client

Woden Contractors

Length

60 metres per bore

Pipe

225mm PVC inside a 450mm steel case

Technique

GBM and thrust boring

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. The major issue on the project was the inconsistency of the ground conditions – bore 1 was in hard displaceable clay, bore 2 was in hard shale, and bores 3 and 4 were in hard rock.

CHALLENGES

UEA used a combination of a guided boring machine and a laser guided rock case boring machine to complete the required on-grade pilot bores. The GBM provided a suitable level of accuracy in the mixed ground conditions at +/- 25mm accuracy. A conventional auger boring machine was then used to install the 450mm steel casing, inside of which the carrier pipes were installed and grouted.

Completion

All works were completed on time and within required tolerances.

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