The tunnelling project consisted of three road crossings, including a 110 m crossing of the Pacific Highway and adjacent wetlands as part of a package of under bores in the Newcastle area. UEA was contracted by Bolte Civil.
The first two drives, both 40 m in length, were driven across the roads using a guided boring machine laser pilot system, which was followed by a traditional auger borer. This method, which is also known as pilot tube microtunnelling, ensured accuracy of line and level and the auger borer provided a simple and efficient method of inserting the 600 mm steel enveloper pipe.
A 450 mm PE carrier pipe was then inserted and grouted into position.
The third drive of 110 m was also completed using the same pilot tube microtunnelling method, ensuring accurate line and level for the enveloper pipe. The 600 mm steel enveloper pipe was installed using a combination of auger boring under the Pacific Highway.Article continues below…
This was then switched to a Grundoram hammer to ensure safe passage beneath the environmentally sensitive wetlands and a flowing creek with no surface disturbance.
With less than 600 mm of cover, the enveloper was successfully installed and the 450 mm PE carrier pipe inserted and grouted into position. UEA said that ground conditions presented hard packed sand through to saturated muds with a high water table.