UEA Trenchless was contracted by CLM Infrastructure to complete a 70 metre 1050mm diameter steel sleeve insertion as part of a reticulation water main renewal for NetWorks Alliance (NWA) in Bankstown, Sydney. Part of this project was located within school grounds and it was essential all works were completed prior to the students return at the commencement of the school year.
During excavation of the drill and target pits, UEA found the ground conditions to be much harder than originally expected. The ground conditions ranged from ironstone to sandstone as well as the expected hard clay. While the ground conditions differed from those originally stated, UEA was confident that they could keep the schedule of works on track and continue with their proposed methodology using pilot tube microtunneling techniques. To mitigate any risk of program slippage UEA kept a Horizontal Directional Drilling (HDD) rig on standby as backup to the pilot tube microtunneling technique .
UEA successfully completed the pilot bore using their Guided Boring Machine (GBM) pilot tube system which was previously untested in these conditions. In doing so UEA was able to maintain critical path and guarantee the program of works. The GBM system performed admirably and accurately – placing the pilot bore to within 20mm over 70 metres.
The risk of using the GBM in these conditions is greatly reduced as the rods are fully retractable and recoverable and the system is quickly and easily setup and removed from the pit. In addition, UEA was able to backup this technique with one of their HDD machines to complete a drive should ground conditions become impassable.
The 1050mm sleeve was inserted with a McLaughlin 36/42c auger boring machine. Site Supervisor Tom Martin said “We were able to operate the borer at full potential with the (GBM) pilot to keep us on course through rock. We spent a day on the pilot but we easily made this back up with the borer. The client is happy with a straight bore and we can feel happy a good job was done.”
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