UEA Trenchless has completed two 60 metre bores beneath the Nepean Highway for Comdain Infrastructure (Comdain) on behalf of Multinet Gas, to facilitate the relocation of natural gas infrastructure. UEA was contracted to install 60 metres of DN450 and DN600 Class 4 RC Jacking Pipe (RCP).
Comdain, on behalf of Multinet Gas, is responsible for the relocation of natural gas infrastructure currently located on Crown land at 1138 Nepean Highway in Highett, Victoria, to a new location approximately 450 metres southeast at Sir William Fry Reserve.
Scope of Works
To facilitate the relocation of natural gas infrastructure, two 66 metre gas pipeline crossings of the Nepean Highway were required. The scope of works completed comprised of two trenchless crossings over the Nepean Highway:
- 1 x DN300 Steel Licensed Transmission Pressure (TP) pipeline within a DN450 reinforced concrete casing
- 1 x DN450 Steel High Pressure (HP) pipeline within a DN600 reinforced concrete casing
The reinforced concrete casing pipes were installed by pipe jacking and microtunnelling, and prefabricated sections of pipeline were installed within these casings.
The geotechnical information provided indicated the ground conditions would be sandy clay and very dense. Two separate launch pits were excavated adjacent to one another, in which auger boring equipment was set up to complete the works. For this bore UEA utilised the Akkerman Laser Guided Boring Machine (GBM) to complete an on-grade pilot bore.
Following the completion of the pilot bores, UEA used a conventional Auger Boring Machine to install the 710mm and 600mm diameter steel envelopers which follow each of their pilot bore alignments. For each of the thrust bores, the auger was placed inside the steel enveloper with the casing jacked into place as the drilling was performed. Once the steel envelopers were installed, UEA jacked in the DN600 and DN450 RCP respectively to replace the steel envelopers, which were removed in three metre sections from the receipt pit as the RCP progressed. The auger assembly was then removed and the DN450 and DN300 gas pipelines were installed on centralisers through their respective RCPs, and once installed the annular gap of each bore was then grouted.
The critical element of these works was to avoid ground syphoning and heave, which would be detrimental to the Nepean Highway. UEA was awarded the boring works when the team presented the GBM’s capabilities and showed that it is specifically designed for displaceable ground.
This project was successfully completed on 9th November 2016 with all bores on the correct grade and alignment.