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Speaker Spotlight: Knut Garshol

ยท 500 words, 2 min read

In the lead up to our Underground Operators 2021 conference, we interviewed keynote speaker Knut Garshol, Rock Engineering Consultant, Sweden to offer insights in his presentation and key issues relating to the industry.

Q. What message would you like to highlight to the delegates at this upcoming Conference? What do you hope will be the main take away from your keynote presentation?

A. By combining immediate and permanent support in D&B tunnelling, construction time and cost can be saved, while significantly reducing the CO2 footprint of the project. Furthermore, that pre-excavation grouting can provide complete groundwater control for the benefit of the environment and prevention of water-related problems in the tunnel.

Q. Many capital cities around Australia have undergone significant tunnelling projects for better transport networks. However, there have been reports that significant technical issues have led to delay and budget blowouts. What is the best tactic to make sure a tunnelling operation remains on track?

A. Without knowing any specifics about the problems described, I can only mention some general points of interest. When technical issues are referenced, it feels right to point out that design and technical specifications must be well adapted to the targeted function and durability of the tunnels. This is certainly self evident, but it is not necessarily easy to establish what it means in each case. When delay and budget overruns become an issue, the two are typically closely linked and may be caused by a host of different reasons. Experience shows that it is always important to have a functional contract model. By that I mean a contract that benefits all parties and supports on-site cooperation. In my opinion, the EPC and turn-key models in their pure form, are not good in this respect. Any attempt at transferring all risk to the contractor has many times backfired and should be avoided.

Q. You have worked on some excellent tunnelling projects throughout your career, specifically the HATS2A project aiming to reduce water pollution in Hong Kong. Are there any other projects you look forward to working on or perhaps a ‘dream’ project that has yet to be started?

A. The bidding documents for the Fornebu subway line in downtown Oslo is currently under preparation for start-up in 2020. The 8.5 km line will pass through intermixed layers of limestone and shale with some igneous intrusions, all the rock types highly jointed. Buildings and infrastructure along the alignment are founded partly on clay-filled depressions in the rock surface and pre-excavation grouting to extremely strict ingress criteria will be a major part of the construction process to avoid settlement damage. I expect this project to be demanding and highly interesting, with some innovative solutions for groundwater control.

Q. Which method of rock tunnelling do you feel is the best overall in efficiency, consistency and sustainability?

A. As the question is phrased and for hard rock tunnelling, I would say D&B is best "overall", due to its superior adaptability in all respects. Variable cross sections, long and short headings, changing inclinations, simple construction of intersections, handling of variable and sometimes unexpected geology and ground water conditions can all be easily accommodated as required. All of this does not prevent that TBM-excavation for individual suitable projects will be the best choice, but the choice comes always with an increased risk. TBM-economy depends on high progress rate and ground- and water conditions being as expected. If not, the sensitivity to deviations may cause serious negative consequences.

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