Tower ad (left) Oct-nov FY21
Tower ad (right) oct-nov FY21

Microtunnelling design 101

Trenchless Australasia speaks to Pezzimenti Tunnelbore’s Jim Shooter about the vital role of the microtunnelling designer and the key steps to delivering a successful design.

What is the role of the designer?

In microtunnelling the detailed designer will define where the manholes are going to be and in what location to minimise disruption to the community and environmental concerns. A designer really has to know not just the constructability boundaries of the project, but also the long-term issues involved in maintaining that asset to make sure the asset is going to be able to service the needs of the client.

What are the key elements of meeting due diligence?

Every designer must keep informed of the technology that is involved at the construction and maintenance phases. They’ve got to be able to provide best value project specific solutions. They go about that like every professional: learning, reading, digesting, talking, and communicating to understand the basic needs the client as well as the ever-changing technologies that are available in the marketplace.

What are the challenges in delivering a good design?

The real challenge is to gather information on the best technology. The other big hurdle is selecting the right pipe materials. A designer has to be aware of what pipe materials are available, but also specifically what materials can be used and in what methodology. For example we often see designers calling up a jacked polyethylene (PE) pipe. A PE pipe can’t be jacked, so the designer knows that PE pipe is ok for sewers but doesn’t know that it can’t be used in certain situations.

Jim Shooter speaking at the NSW Technical Forum in April.

How does the designer obtain specialist information?

Sydney Water has now established a new process prior to detailed design requiring industry input; they are recognising the importance of the designer being informed by specialist contractors. So Sydney Water, and I’m assuming other clients, build into their project development process an allowance for the designer to go out in the industry and talking to specialists.

Are there intellectual property issues when talking to designers before the design is finalised?

If a designer comes to us (Pezzimenti Tunnelbore) requesting information on a design, we tend to talk in terms of outcomes, benefits and possibilities. Rather than us needing to mention how our microtunnelling head works, we say “Look, we can do a 350 m long intercept bore in this type of ground and if it’s this type of ground you don’t need this, you just need this.” We will also give designers outcomes instead of giving them too much of the detail of our technology. We can overcome intellectual property issues by talking in terms of outcomes rather than how it is that we are able to achieve those outcomes.

What is the impact of bad design?

One of the impacts is that, if a design is not appropriate it goes to the principal for approval, it can get rejected because it’s just simply a bad design that hasn’t considered various factors. So in terms of the approval process, time get wasted.

On the other hand, if a bad or very conservative design gets through it can emerge that you don’t actually need to have really thick pipes, outer casings, or certain other things that are adding dollars to the project. Most of the time these dollars are coming from the tax-payer, and conservative designs can result in unnecessarily high costs. So from our point of view the impact of a bad design is that we, as a microtunnelling specialist, have to compete with other technologies.

To be specific – microtunnelling has got to compete with open-cut trenching, and so if a designer comes up with a bad design that is very costly, and the dollars per metre is very high, microtunnelling is less likely to be seen as cost-competitive when compared with open-cut trenching. So a bad design can actually do an enormous disservice to the overall perception of Trenchless Technology.

This article is the first in a series looking at microtunnelling design and project delivery. The December edition of Trenchless Australasia will look at the history of microtunnelling across the region. If you would like to know more about microtunnelling, or are interested in joining the ASTT Microtunnelling Special Interest Group (SIG) please contact Annie Ferguson on

This article was featured in the September edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet, or mobile device, click here.

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