At a build length of 1,163 metres, the pipeline installed by Rob Carr as part of the Ironbark Joint Venture on the Thornleigh Inlet Outlet Main Pipeline Duplication (TIOM) project in Sydney might be a record for diameter in Australia.
The recently completed works are part of two separate project approval sections for Sydney Water and include the North West Wastewater Connection (NWWC), a more typical microtunnelling application.
The duplicate water pipe connecting the Thornleigh Reservoir to the pump station will allow filling and emptying to occur simultaneously.
The single pipeline, at present, is used for both processes and hence limits operational flexibility and optimal utilisation of the large capacity of the reservoir.
Furthermore, by having a separate inlet and outlet to the reservoir it will help to turn over the water in the reservoir more frequently which effectively assists with water quality.
Rob Carr is a 50 per cent partner in the Ironbark Joint Venture along with Bouygues Construction Australia who holds the other 50 per cent.
Not unlike most major projects, there are immense challenges to overcome. In this case the timing between the initial award of the project to the commencement of works left less than 12 weeks to prepare the Herrenknecht AVN2000 boring machine Rob Carr’s sister company Bessac had assigned for the work.
Designed for a pipe diameter range of 1.8 to 2-metres, the unit undergoes modifications between projects so as to meet the distinct specifications of each.
With Bessac’s engineering facility situated in Toulouse, planning was going to be very different for a project in Australia in which designers would need to anticipate a range of requirements such as the geological environment and the diameter of the tunnel ahead of the microtunnel boring machine’s deployment.
Rob Carr and Bessac worked closely to ensure the preparation of the AVN2000 was expedited to factor in the three months at sea its transportation would take.
The shipment itself involved serious logistics.
“There’s also associated equipment for the tunnel itself along with the microtunnelling machine,” said Thomas Blanchard, Bessac Construction Manager.
“It takes almost 20 40-foot containers sent via ship.”
The original plan was to have a DN1800 steel cement lined pipe installed within a DN2100 reinforced cylinder concrete pipe.
That would entail a fairly typical microtunnel whereby a larger DN2100 reinforced concrete jacking pipe acts as the enveloper pipe, with a separate DN1800 steel pipe with cement lining installed and grouted in place within the enveloper.
Upon review, however, the Ironbark Joint Venture suggested to the client an alternative solution.
A reinforced cylinder concrete pipe (RCCP), they proposed, could reduce the risk of leaks, rising costs and downtime in planning, and alleviate mounting pressure, measured as high as 17bar on the original pipeline.
“Sometimes when we have a pressure pipeline as we have on this one, the concrete pipes are not sufficient for controlling the leaks because the pressure is very high,” said Blanchard.
“In the end we went with a 1.8m internal diameter concrete pipe with a steel pipe already inside.
“We basically kept the same outside diameter of roughly 2.4m and installed the finished pipeline in one go as the complete solution was an all-in-one pipe. There was no additional process which would have required us to weld, pull the steel pipeline through the centre of the concrete enveloper and grout.”
Additional valves were installed to bolster controls on the dual pipelines through both the reservoir and the pump stations. “Temporary works designers had to be very specific about how to detail the tunnel and how to execute the jacking,” said Jonathan Hill, Ironbark Project Director.
“Such as having intermediate jacking stations to ensure we were able to complete such a long drive without having problems in the ground.”
Operations were 24 hours, five days a week with a half day on Saturdays.
A full day was split into two 12-hour shifts that overlapped so that crews could understand what had happened on the previous shift.
Of course, handovers between these shifts were of the utmost importance. Here the skill shift teams discussed what was achieved on the previous shift, what needed to be done, any issues encountered and whether the cutting head required replacement.
Professional engineers, supervisors and pilots on both shifts come together.
On the AVN2000 used, the diameter of the cutting wheel was changed prior to deployment in order to facilitate a bigger external diameter necessitated by the thicker pipe.
One of the striking features of Sydney, for anyone who encounters it for the first time, especially by air, is how prominent the landscape is with sandstone. There are outcrops and abutments as far as the eye can see.
The abrasive nature of pure sandstone normally would require use of a hard rock cutting wheel but because the drive was so long at 1.2km, the Ironbark Joint Venture opted for a cutting wheel armed with a blend of discs, which are useful for rock conditions, and blades that adjust better to the softer, clay conditions that would be encountered infrequently.
At different intervals, as progress is made, the cutting head is assessed for wear according to Hill.
“It’s not necessary that all of them are being worked as hard as each other so we might have to replace a couple of them at that point,” he told Trenchless Australasia.
“We measure the amount of reduction in the diameter of the cutters and then we plot that determining how many millimetres we have lost of cutter in a certain distance and then we will go back in again for another section to replace the others.”
Ironbark Joint Venture utilised a bentonite recycling system on all the control units for slurry removal. NWWC, which consisted of two drives, a short one from Receiver works at the Rouse Hill Water Resource Recovery Facility to Lot 96 of about 80 metres and another of 710m from Lot 96 to a pump station where the TBM was ultimately retrieved, featured picture book ground conditions in comparison.
TIOM proved a little more challenging leading to a slight difference in productivity. The team, led by a knowledgeable construction manager, adapted quickly according to Hill.
“We maintained progress and the team worked together to find solutions,” he said.
“It was crucial that supervisors worked with personnel on debriefings, so they understood the work scope and the clarity of mission.”
Establishing a clear step-by-step methodology for how to execute the works in detail, for each person’s role and responsibility within the works, helped.
“We ended up having to keep a tight specification for the installation of the jack pipe and at the head of the microtunnel there are jacks on the cutting head so that we can steer the microtunnel,” added Hill.
“As we do that, we have continuous recording of where we are in the control cabinet. Then under frequency we take a survey as well to check where the MTBM is at, and we arrived within 20mm of its finished position at both distances and that’s nothing given the fact we’re talking about a no-dig.”
Both jobs, what’s more, were completed in sensitive environmental areas.
Thornleigh backs into a corner where there is housing on both sides making the task challenging.
One of the main challenges was to understand how crews could work 24 hours a day without disturbing the neighbours. Noise barriers were situated around generator systems.
Hybrid electrical systems rather than diesel generators helped to greatly reduce noise level at night. The quietness of the drainage processes was also evaluated.
High hoardings were erected around the site to diminish the noise paths to the neighbouring houses.
“Special care at night was taken not to move equipment that would create an ad hoc noise which tends to disturb people when they are sleeping,” said Hill. “We had strict controls over what activities could take place and where they could take place, well within our noise levels permitted by the Environmental Protection Agency. It was a successful job.”
The choice to go with the one pass system utilising the reinforced concrete cylinder jacking pipe also drastically reduced transport and storage.
“We didn’t have to use two separate transports to bring in the concrete pipe and all the steel pipes. It was only one single transport,” said Blanchard.
“Nor do you have to inject the grout between the steel pipe and the concrete pipe because the steel pipe is already in the concrete. That has a huge reduction on the overall carbon footprint.”
It’s also a solution never previously used before in Australia. With a blend of supervisors, engineers, mechanical experts and tunnel boring assets used to deliver these ambitious tunnelling works, the Bessac and Rob Carr teams were truly integrated.
As Bessac doesn’t nominally work within Australia, having sister company Rob Carr as a major partner in the JV greatly assisted project synergies to ensure major milestone were achieved.
“Projects like TIOM and NWWC are exactly what group partnerships are built for,” said Angelo Soumboulidis, Rob Carr General Manager.
“Rob Carr brings the local knowledge, experience and capability along with a clear understanding of local conditions. Bessac brings the engineering depth of one of Europe’s foremost tunnelling specialists. By combining those forces you’re not just putting a tender together, you’re lifting the standard of what’s deliverable for the client.”
For more information, visit robcarr.com.au
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