With a variety of microtunnelling methods and systems to choose from, it is important that you select the right technique to suit your individual site and project specifications. For contractors, it is crucial to work with a machine that is versatile and able to manage a wide range of ground conditions, with a variety of pipes and configurations. However, many systems lack this versatility.
The lack of versatility in many microtunnelling systems can cause problems when conditions are different than expected, as can often be the case. When a rigid system is used, it is hard to make adaptations and this can cost clients time and money.
Inside Construction sat down with Edge Underground managing director Stuart Harrison to discuss how the Vermeer AXIS guided boring system can provide versatile microtunnelling at minimal risk.
Pilot lines are key
According to Harrison, unlike traditional pilot microtunnelling systems which displace the ground, the Vermeer AXIS installs pilot lines via a vacuum extraction method.
The Vermeer AXIS is designed to cut and extract the ground as it moves, and in doing so, has little to no influence on the ground directly surrounding the installation. This allows microtunnellers to visually inspect the condition of the earth that is being excavated at the face.
Harrison said knowing the existing ground conditions, and being able to adapt to them, is the key to getting a microtunnelling job completed with minimal risk.
“The Vermeer AXIS guided boring system gives contractors the ability to retract, access and change the machine head part way through drilling the pilot line. Contractors are able to configure the cutting tool to test for changing conditions before committing to jacking the final line,” Harrison said.
Unexpected ground conditions
When it comes to planning for a microtunnelling installation, it’s important to remember that the information provided by geotech surveys does not always give the complete picture of the ground conditions, or they may be incorrect.
This is why the information a pilot line provides to contractors is so crucial. Beginning a microtunnelling project where the exact changing ground conditions are unknown can create numerous problems, that cost time and money.
According to Harrison, most microtunnelling machines can only move in a forward direction. This means once drilling has commenced, if the chosen cutter is not suitable to the ground conditions encountered, the best option is to dig a shaft down towards the drill before changing the head.
“The advantage of the Vermeer AXIS system is its ability to come back, retract and change bits. There’s no impact to the ground and you can swap parts and cutter face options to boost drilling performance in most ground conditions,” Harrison said.
“Having a machine that can be setup to suit whatever the ground condition is gives contractors the ability to determine a better setup for the machine to ensure that the installation is done effectively and efficiently.”
Suitable for a range of diameters
Different projects will require pipes of a certain diameter to be installed. Traditional microtunnelling systems need customised drill heads to allow for the installation of different sized pipes. This can become expensive, especially when it is a size the contractor may not use again.
Harrison said the Vermeer AXIS system only requires one drill head to complete a pilot line and it’s just a matter of changing the size of the reaming tool to achieve a range of diameters. Importantly, the cost of these reaming tools is relatively inexpensive.
“Vermeer AXIS is regularly used to install pipe in the 300-600mm range, and to date, the largest ever installation was a 900mm pipeline,” Harrison said.
This versatility is due to the fact that the Vermeer AXIS system can install pipe via either the pilot and pull back method, or the jack and ream method. This allows the contractor to be flexible when choosing the installation method best suited to the site and lowers installation risks, as it uses the pilot line created by the drill head between the launch and exit pits to pull or jack back the pipes.
Pipe selection
Traditional microtunnelling methods typically rely on the use of jacking pipe, as it transmits the thrust from the jacking station to the drill head to progress the line. However, with the Vermeer AXIS system, the use of its unique pilot line method creates a situation where, in self supporting ground, the force on a pipe would only be the weight of the pipe itself. In this case, the pipe selection only truly relates to the ground conditions.
“Vermeer AXIS is able to install a wide range of pipe types, including both rigidly constructed, as well as fusible and restrained joint product pipe,” Harrison said.
“This versatility gives clients more product pipe options based on factors such as existing ground conditions, costs, traditional preference, and matching with existing infrastructure.”
Low cost production
Microtunnelling installations can be expensive, especially when compared to open-cut installation methods. Therefore, a machine that is able to keep the costs down will be more competitive.
A system such as Vermeer AXIS does not require structural pits when the ground conditions are relatively stable. It’s the combination of a carefully designed drill head with a vacuum extraction method that allows it to effectively core its pilot hole through the ground, leaving a dry and stable pilot hole. Compared to other microtunnelling systems, the Vermeer AXIS-guided boring system requires a low amount of thrust and pullback force to create a bore in these relatively stable conditions.
“This means it doesn’t need a structural backstop or shaft constructed in the launch pit, reducing the costs and saving time as machine preparation is minimal,” Harrison said.
It also offers precise on-grade drilling to within +/- 5mm. The system utilises a CCTV camera that is built into the drill head to allow the contractor to constantly monitor the process of the drilling. Using a laser as a guide, the operator can make adjustments to the steering of the drill head to ensure line and grade is maintained.
Furthermore, compared to open-cut methods the Vermeer AXIS guided boring systems has minimal restoration costs. All that is required is the surface excavation of two pits that can serve as the manhole locations. This saves additional excavation time and resources, and reduces surface reconstruction costs.
The Vermeer AXIS guided boring system can also be configured in a number of ways depending on jobsite footprint and transport considerations to limit its impact on the surrounding area.
Minimising risks
According to Harrison, microtunnelling with a versatile machine essentially comes down to one simple concept: risk minimisation.
“When it’s all said and done, we are all looking to reduce the risk on our trenchless projects to make it more cost-effective and competitive,” he said.
If you are a microtunnelling contractor looking to join a highly skilled team, or would like to learn more about the Edge Underground call 1300 JACKED.
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