Justification of a novel pipe-in-tunnel approach to a river crossing
by Chas Jandu, Mike Taylor, and Stephen Humphrey, Andrew Francis & Associates, Ripley, UK. Trenchless Australasia — Trenchless Australasia October 2010
As part of a major pipeline construction project, Laing O’Rourke was required to install a section of pipeline beneath a river estuary. Due to a number of reasons it was not possible to negotiate the crossing using conventional techniques such as horizontal directional drilling (HDD) and an alternate method had to be sought.
A feasibility study was undertaken and it was decided that a pipe-in-tunnel approach was the most viable. Due to constraints at the points of entry and exit it was necessary to cut two vertical shafts, one on each river bank. Linepipe sections were to be welded together, in the entry shaft, and pulled through the 2.44 m diameter tunnel on plastic rollers, which were later to become the permanent supports during operation. On completion of the installation within the tunnel, two vertical sections of pipeline were to be installed in the shafts for connection to the main pipeline system. Based on the results of the study it was possible to show that, with a number of modifications to the originally-proposed design, the crossing would be fit-for-purpose.
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