Having the right equipment for an HDD crossing is, understandably, crucial in ensuring the crossing can be, and is, completed to specification. Making sure a rig can comfortably achieve the length of the crossing, the radii required, the entry and exit angles, and so on, and the other equipment in the spread can too, is a basic requirement of every HDD job.
But when a project’s stakeholders truly want to leave as little as possible to chance, and to really see the HDD method shine, an additional step should be taken: optimising the crossing for the equipment.
Flexibility for success
Such was the case on a recent HDD project in Rochedale, Queensland, Australia. HDD Contractor SEQ Trenchless was tasked with delivering the HDD installation under Bulimba Creek and the busy South East Busway to enable installation of a high-voltage, nine-conduit feeder bundle as part of the larger Brisbane Metro Project. With only a narrow construction corridor available adjacent to another busy road, sandstone ground conditions, and plenty of services to avoid, the crossing had its complexities.
With project factors and initial recommended designs indicating the crossing would require a midi class rig, SEQ Trenchless knew this was the perfect job to showcase its brand new Tracto Grundodrill 28N rig.
SEQ Trenchless Director and HDD Consultant, Josh Taylor, said the rig promised to punch above its weight in the midi space. “There was a lot that interested us in the 28N. Its features and capabilities have the potential to really push the limits of what can be achieved with a rig of this class, and we were keen to show thi soff at Rochedale.” Josh said. “Compact enough to fit in the small available space, but promising some impressive power specs and features, we were keen to see what it could do. ”
Josh said that as well as having the brand-new rig on site, the project benefited from a client that was experienced in using the HDD method and open to ensuring risks were mitigated and advantages maximised.
“Our client, Diona, was really supportive and motivated in ensuring the HDD was optimised for success, while keeping a conservative, risk-averse approach.” Josh said. “This flexible attitude meant we had the freedom to apply some adjustments to the initial designs, tweaking to suit our equipment and methods. We did things like reducing the depth of cover slightly to be in range of walkover steering, but still providing adequate depth of cover to mitigate hydrofracture risk, and adjusting the entry angle to suit our vice heights, small changes, but a really worthwhile step in ensuring the crossing would go off without a hitch.” he said.
Compact rig, big capacity
Drilling of the 308 m crossing commenced in November 2022, with Director and Drill Supervisor Shaun Newbigging on site overseeing the new rig’s capabilities.
“This was the perfect job for the new rig, 28 in (710 mm) diameter in rock conditions, with a horizontal curve and grade, all next to and under busy roads and a creek, plenty to contend with.” Shaun said. “But we found it really performed, with a great balance between power and responsiveness.” he continued.
“To ensure a good maiden voyage, we used a mud motor in a straight housing at the end of the drill string, with rock breaker sonde assembly in front. This was key for reducing steering lag in these variable strength ground conditions, as well as metro jobs where existing services are a factor.” Shaun said. “We also had to switch the rig orientation for pullback, so we got a good appreciation of the easy setup and demob arrangements for the rig, which was a plus.”
TRACTO Australia Sales Manager Daniel Toms agreed that the flexibility of the 28N opened up opportunities for contractors in the midi rig sector. “The 28N brings the best of both worlds, with plenty of power, but remaining nimble and able to be compressed into a really small construction space.” Daniel said. “It punches above its weight in many ways, with a 288 m rod magazine, 650 l/min pumping capacity, and 28 t pull/thrust capacity and a maximum torque of 8,000 ftlb (11,000 Nm).” he said. “This makes it perfect for small jobs, but it can comfortably stand on its own two feet when taking the next step up into longer and larger diameter crossings, even in hard rock.” he said.
However, Daniel said it was the smart features of the 28N which brought even more value for contractors. “With a variety of automatic functions, like semi- and fully-automatic drilling modes, automatic rod exchange, and even automatic cleaning of the drill rods, these modern rigs are safer and easier to operate than ever with a small crew.” Daniel said. “Paired with unparalleled data logging and data transfer capabilities for today’s HDD designs, contractors have all the information and tools to not only be efficient and effective on this crossing, but to review and improve for the next one.” he said.
One down, many more to go
The rig’s maiden crossing was delivered to great success, with pullback of the bundle completed without incident. Josh said while good design and fit-for-purpose equipment were two important factors, the cooperation of all stakeholders was critical to the high level of success achieved on the Rochedale project.
“We really need to pay credit to the supportive, flexible approach by Diona, and their commitment to enabling us to adjust the crossing to minimise risk and complexity.” Josh said. “Paired with the support from TRACTO Australia in getting the most out of our new rig, we are pleased with what we achieved and are looking forward to many more successful crossings with it.” he said.