In the past, very hard rock has posed a problem for microtunnelling machines, with most tooling struggling to successfully drill through it to install a pipeline to specifications. This means most contractors turn down projects where the geotechnical information has identified this ground condition or stop a job part way through when they unexpectedly hit very hard ground. A new drilling tool – an air hammer – has been designed and proven to work in very hard rock while maintaining accuracy, productivity and efficiency, and providing additional environmental and work health and safety benefits.

Drilling through rock

The new technology was inspired by the increasing need for drilling rock on fine grades and a lack of options available to do so with high rates of success and/or time and cost efficiency.

This new drilling tool is based on a new pneumatic rock hammer – which uses air driven hammers (similar to vertical DTH heads) – that Edge Underground had just developed and proven on-site using prototypes to advance the capabilities of its AXIS laser guided boring machine. It is ideal for use in very high strength rock.

Maintains accuracy

When using the new air hammer, a pilot line guides the head to maintain accuracy. It can be operated via the next generation AXIS drill rods with a power enhancing driver, and has been tested and proven with the extra heavy rods of the AdaptX – a new machine on the market with unparalleled capabilities, manufactured by Bournedrill. 

Environmental and WHS benefits  

The new tooling also has environmental and workplace health and safety benefits. It enables small to medium size pipe diameters to be installed in hard rock faster, with a significant reduction in spoil removal and truck movements compared to open cut methods. 

Furthermore, when used in conjunction with the ‘keyhole’ pipeline installation method – pioneered by and synonymous with Edge Underground – it further reduces the amount of excavation required for smaller diameters, which in itself greatly improves the health and safety outcomes on-site.

Proven in the field

This technology’s ability to work in high strength rock was proven in a recent project in Donnybrook, Melbourne, where it was successfully used to install a pipeline in 250MPa+ basalt.

The project was for Yarra Valley Water (YVW), with Edge Underground and Diona contracted for the works. In order to meet all the technical requirements, Edge Underground needed to utilise many of the upgrades to its AXIS system. At the time, the upgraded system was untried. After many discussions, YVW, Edge, Diona and Bamser worked collaboratively and concluded this was a perfect opportunity to test the new concept.   

This system was used to overcome the very difficult ground conditions. Without it, the only other option would’ve been to upsize from DN700 to DN1200 and install concrete casing pipe – a greater cost to the client. 

The result was a great success, with the technology surpassing all client expectations; microtunnelling on average four times faster than a conventional system, avoiding the need to upsize to a far larger diameter, and saving time and money. 

The air hammer is a new innovative technology to the microtunnelling market, and has been patented by Edge Underground.