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From Risk Aversion to Risk Reduction: How Elon Musk could usher in a New Era of Tunnel Boring
Tunnel boring machines like the one here, for New York’s Delaware Aqueduct Repair, are turning risk aversion on its head.
It has been some time since I have written on the Robbins blog page, but I am inspired to do so by the announcement that Elon Musk is entering our business—the tunnel boring business. It is great to see people with a vision of an improved world enter our industry. I agree with Musk that the advance rate of tunnels can be significantly improved if development money comes into the industry. Development money in tunneling, however, is at best minimal and is more often essentially nonexistent. Nearly all tunnels are heavily specified to avoid risk taking by owners (therefore discouraging new development). Nearly all tunnels go to the low bidder and low bidders try to buy the TBMs at the lowest price; a further discouragement of development. The industry has therefore been slow to improve advance rates, but with Musk bringing the issue into the spotlight, perhaps things will change.
Risk Aversion and How to Reverse it
There are some exceptions to this practice of risk aversion for new technology, and one is the Delaware Aqueduct Repair. This tunnel corrects heavy water leakage occurring from the 1940’s-built aqueduct tunnel for New York City. We are just completing Factory Acceptance in our plant in Solon, Ohio of this unique Single Shield TBM. The tunnel is at significant depth (approximately 300 m / 900 ft) with the distinct possibility of encountering very high water pressure (up to 30 bars). The contractor JV of Kiewit/Shea have shown their willingness to move forward with several new developments for this project. The concept of grouting off high water pressure as the primary means to allow advance in such conditions, rather than use an EPB or Slurry TBM, is in my view a significant step forward for our industry. Granted there have been halfway attempts with a combination of grouting and pressurized tunneling at recent projects like the Arrowhead Tunnels and Lake Mead Intake No. 3, but these have come at high cost and sometimes long delays. The Delaware Aqueduct TBM, by contrast, is designed to hold up to 30 bars of pressure while grouting occurs. Boring and cutter changes are done in atmospheric pressure.
Chemical grouting and grouting technology in general have advanced multifold in recent years, and it is commendable to see it used extensively on several aspects of the Delaware Aqueduct Project. It’s a great example of what can be done when a contractor is willing to use new technology to address potential risks—it appears it can actually reduce risk in the long run. It is a great honor to be working with the capable Kiewit/Shea JV team to be a part of advancing technology.
The enhanced probe drilling and grouting capabilities as seen in trajectories (orange and red) on the Delaware Aqueduct TBM 3D model.
Areas Ripe for Change
The Delaware Aqueduct Repair project is a flagship project for what I hope will become more common in the industry: instead of low bidding with the cheapest possible machine, offering a reasonable bid with a specialized TBM that has a higher initial investment, but ultimately a lower cost overall. The project’s use of technology is wide-reaching, particularly atmospheric cutter changes and chemical grouting, which have the potential to reduce downtime and increase safety. I do not see the future of rock tunneling under high water pressure being left to divers to change cutters and repair the cutterhead. We all know it is not cost effective to send divers to work in confined spaces over 10 bars. It should be noted that the long-duration Hallandsås Tunnel, for example, finished the majority of its TBM advance by relying on effectively this technique of grouting and advance after failing with a Slurry System. There are lots of tunnels to be built with above 10 bars pressure that will use this technology. The industry needs to automate cutter and bit changes as much as possible, and increase the integration of chemical grouting in tunneling.
Niels Kofoed and Danny Smith of contractor Kiewit examine the cutterhead and cutters of the Delaware Aqueduct TBM. The machine can bore and cutters can be changed at atmospheric pressure.
Certainly there are many areas for advancement in our industry, and major public figures like Musk drawing attention to it is ultimately a good thing. After all, getting the general public to think about solving traffic by going underground is no easy feat. Even more so, getting the tunneling industry to think about its own risk-averse practices has a big potential benefit. Hopefully all of this attention will result in more tunnels, more business, and better infrastructure. Musk’s willingness to take a risk aimed at making the underground construction industry potentially faster and more stable is a good bet to take.