From the magazine, Microtunnelling, Pipe jacking, Tunnelling

Microtunnelling comes to the rescue

With construction spending down at present, Pezzimenti Tunnelbore New South Wales Manager Jim Shooter says tendering prices are being driven lower and lower as companies compete fiercely for the work available.

Mr Shooter says “Companies are being forced to take on increased risk in order to win work and stay in business. Increasingly, some companies are taking on risk which they cannot manage, overstating the capabilities of the technology and hence the level of service they are offering”.

He warns project owners to be wary of this fact when selecting a contractor, and to be sure the selected contractor is capable of providing the services they lay claim to.

Taking over a challenging project

Recently Pezzimenti Tunnelbore received a call from a builder who was constructing a block of units. The owner required a bore to be completed for a
150 mm sewer main. The length was to be 75 m, with the bore designed 5.2m deep at the upstream end. At the downstream end, the 150 mm pipe would drain into an existing sewer manhole 3.4 m deep in the middle of a “÷T’ intersection. The plan was to drill directly into the base of the existing manhole, which would eliminate the need to open up the road.

When Pezzimenti Tunnelbore received the call from the builder, the project had already been attempted by another contractor but was unable to be completed using the previous company’s chosen method of trenchless installation.

In order to prepare the works for the first contractor, the builder had excavated a very large shaft in competent sandstone approximately 10 m long, 4 m wide and
6 m deep to accommodate the contractor’s machinery. The timing of the new sewer construction was critical, as the existing sewer ran directly through the block of land being developed. Construction of the units could not proceed until the old sewer was diverted through the new sewer. Completion of the new sewer was on the critical path for the entire development.

When Pezzimenti Tunnelbore was contracted, building work on the site had stopped, the previous contractor had run out of options, and the builder’s costs had escalated due to the delays incurred.

Moving to microtunnelling

Pezzimenti Tunnelbore inspected the site, decided against trying to recover the failed bore from the previous contractor, and suggested setting up a new launch shaft. Pezzimenti Tunnelbore advised the builder that they would complete the works by using the proven and established technique of laser guided microtunnelling. This technique was introduced into Australia by the Pezzimenti family of companies in the late 1980s. Laser guided microtunnelling has developed to the point where it has become routine to microtunnel up to
350 m in sandstone reliably and accurately.

Pezzimenti Tunnelbore was able to set up a 4×2 m shaft in the ramp previously excavated by the builder to get access to the much larger shaft required by the previous installation technology.

Mr Shooter said “The builder had the redesign approved, we established
on-site and work commenced. For a laser guided microtunnelling system, the bore was a very simple one. The drilling took just two days and the builder was visibly relieved when the microtunnelling head exited into the base of the existing manhole-spot on target. The PVC pipes were sliplined into the bore and the annular space grouted.”

Since that time Pezzimenti Tunnelbore have been requested to complete works on several other sites where again the initial contractor was unable to complete the works using a different technology.

Mr Shooter summarised by saying “The initial lowest price is not always the best value at the end of the project for the client.”

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