While microtunnelling machines have traditionally been used for pipeline installations, their versatility has seen them increasingly used for projects beyond their original scope. More projects are seeking the advice of expert microtunnelling contractors to provide an innovative drilling or boring solution for infrastructure projects.
A growing market
One of the areas where microtunnelling machines are being used more is for tunnel canopy supports which are installed to reduce the occurrence of subsidence in structures that are above the proposed route of a tunnel during excavation.
Tunnel canopy supports consist of numerous bores—ranging from 150mm to 1200mm in diameter—with a 50-70mm separation between the pipe walls depending on ground conditions at the site. Pipes can also be attached during installation using clutches which reduces the chance of material falling from above the pipe canopy into the tunnel during construction.
These pipes can be filled with grout if the canopy is being used for temporary support, or a steel reinforcement can be installed into each bore which is then filled with concrete if the canopy is a structural component of the tunnel.
Stuart Harrison, Managing Director at Edge Underground, said that while tunnelling is a great solution for larger infrastructure works, the capital outlay for a tunnelling machine means that it is prohibitive when contractors want to take on jobs which are relatively short in length.
“By using microtunnelling machines, contractors are able to complete multiple small passes, and then effectively you join the small passes to create a larger tunnel.
“This is an approach that’s been effectively used and it works out a lot cheaper than using a tunnelling machine.
“Typically a tunnelling machine, depending on the size, may need 100m of space just to set the machine up before it starts. So if you’ve got a job and it’s 40m long, for instance a pedestrian pathway, and you needed a six or 10m diameter tunnel, you just don’t have the physical room for a tunnelling machine.”
With canopy tunnels gaining momentum in Australia and a number of them completed in New South Wales, Victoria and Queensland, it provides a new area of growth for microtunnellers as the installation needs to be precise, and microtunnelling is the most accurate trenchless solution available.
“It’s another whole area in microtunnelling. If you need to be precise, then microtunnelling gives you another solution,” Mr Harrison said.
“I’ve only been involved in consulting on them so far as they’re a large project done by companies that are generally fairly tunnelling oriented, and they like to try and do as much as they can themselves.
“Some of them have come across some problems and that’s where I’ve come in to consult on them because they’ve gone in with an approach that was fairly limited due to the style of machine they were using.
“These are areas that are pretty uncapped really in Australia. We’ve only seen them on a few occasions, but they give you a huge amount of scope that probably isn’t understood by the engineers just yet.”
Microtunnelling can also be used to provide innovative solutions to challenging problems.
Mr Harrison said he has been called onto projects in the past to devise a solution to a problem that was not typically seen in the scope of a microtunnelling contractor.
“I was called in on a project to provide a solution to underground water pooling. The concern was that if the pooling continued it would rise up to the road.
“I suggested that two microtunnelling bores should be completed, trapping the pooling water and giving it an easy path to a nearby draining system. By drilling these below the road surface, the water would be able to travel down to a collection of pits rather than travelling up to the surface.”
The bores were completed overnight using the AXIS laser guided boring system at 350mm in diameter, with 150mm PVC pipe installed inside.
“Microtunnelling is versatile and can be used for more than just pipeline installations. By consulting an expert contractor, a drilling or boring solution can be explored to solve construction problems that you may not have considered before,” Mr Harrison said.