Scope of Works
To open cut and lay the steel enveloper pipes using conventional trenching methods would be problematic given the location and depth and was deemed unsuitable as it would require closing the Gold Coast Highway at Broadbeach. Furthermore, ground conditions consisted of unstable fine sand, typical of the Gold Coast area, which had seen other contractors undermine the main highway throughout the Gold Coast precinct. This was a key factor in identifying pilot tube microtunneling using a guided boring machine as the most suitable trenchless method for completing the crossings successfully.
UEA Trenchless did not experience any undermining or over excavation subsidence on the drives using the pilot tube microtunneling method giving the principal contractor Baulderstone confidence that strict tolerances of grade and safe clearance from existing infrastructure could be constantly met. As such, the reduced risk provided by the guided boring machine meant UEA could work under full highway traffic avoiding costly night works which was beneficial to the client.
The project design had been completed by another contractor so UEA had little to no input in how the project was to be constructed which presented a number of challenges. On the first bore the pit dimensions were reduced which meant UEA had to install 3 metres lengths of steel enveloper pipe, as opposed the preferred 6 metre lengths, which doubled the installation time by increasing the number of welds.
The second bore of 40 metres was installed smoothly in half the time thanks to a vacant block of land which allowed for the construction of a larger entry/exit pit.
Once the first 30metre bore was installed it was resurveyed and found to be only 1mm out from the design, well within tolerance and industry standard. Several local authorities visited site to witness pilot tube microtunneling first hand – a great way to gain an understanding of the various and ever changing trenchless methods available.
Once the steel enveloper pipe was installed the DICL pipe was inserted using an auger boring machine to jack the pipe through, after which the annulus was filled with an approved grout mix.
Since completion of this project UEA has utilised pilot tube microtunneling to complete longer and larger diameter installations in more difficult water charged ground conditions near Newcastle.
For further information on this tunneling method please email firstname.lastname@example.org