Poatina Tailrace Tunnel – The Mole

The Poatina Tailrace Tunnel project holds a unique place in Australian tunnelling history, yet little has been published about its construction and, in particular, the excavation performance of the Robbins tunnel boring machine (TBM) employed on the project. In this issue, we are pleased to publish a paper originally written in 1963 by Peter Fletcher, then an undergraduate engineering student at the University of Sydney.

During his third year of study, Peter had the opportunity to work on site for the initial six months of tunnelling at Poatina, reporting to Allen Neyland. His primary task was to conduct a detailed spoil haulage time-and-motion study, ensuring an empty rake was in position under the Dixon conveyor at the start of each TBM stroke. This work later formed the basis of his university work-experience report. However, Peter’s close involvement with the TBM operation and performance also led him to write the article reproduced here, which was first published in the 1963 Sydney University Engineering Year Book with the approval of the Hydro-Electric Commission.

At the time, Peter understood the Poatina TBM to represent an Australian first. In the decades since, it has become clear that this project holds an even more remarkable distinction: it is claimed to be the first successful TBM infrastructure project completed anywhere in the world.

Now, more than sixty years later, Peter revisited his original article and, with the benefit of hindsight, offered the following two clarifications to his early observations. He says his opening comment, that TBM’s had been used in America in recent years, applies to Robbins mining equipment, successfully developed to excavate exploratory adits. In addition, his concluding comment, that a TBM would be unsuitable for extensively fractured rock conditions, was based on experience gained with a TBM designed specifically for hard rock conditions. At that time, he says he did not appreciate the manner in which TBM technology would subsequently develop.

The ATS is delighted to present this paper, both as a historical record and as a reminder of the pioneering spirit that has long characterised tunnelling in Australia.

The Mole without introduction_FINAL NEEDS TO BE PUBLISHED ONLINE