A cut above: Tunneling cutterhead arrives in L.A.

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Like the first flowers of spring – although substantially larger – the tunnel boring machine cutterhead arrival at the Metro yard this week is a harbinger of the future. In this case it’s a future of exciting Crenshaw/LAX construction to come. Although not particularly attractive to most of us, to subway experts it’s a thing of beauty because it means the process toward digging the tunnels needed for the underground portions of the line is proceeding.

The cutterhead is the circular rotating face with teeth that is attached to the front of the tunnel boring machine. It chews up the soil and pushes it backward through the boring machine to help create the subway tunnel. The soil is then collected and carried away.

Yesterday night’s cutterhead arrival, carried on a flatbed truck, was through the Port of Long Beach via ship from Germany, where it was manufactured.

Digging the tunnels between the three underground Crenshaw/LAX stations won’t begin for many months but the march of the cutterhead through darkened L.A. streets – accompanied by six CHP vehicles to ensure safety – was an exciting milestone, reminding us that massive projects like rail lines happen through hard work and a series of tiny steps, not through miracles.

For an explanation of subway construction, see this post.

14 replies

  1. I’ve never understood why so many people (myself included) have such an enduring fascination with mechanical moles. After all, when you get right down to it, they’re really not all that interesting: just big, boring machines.

  2. I notice there hasn’t been a single mention of a tunnel boring device known as a ‘SUBTERRENE”. This machine (which rhymes with “submarine” ) uses plasma torches in place of cutter heads/wheels to bore the tunnel ahead of itself. There is no “muck” (earth to be removed as a result of tunneling), because the subterrene simply melts the rock and pushes the fluid to the sides (or edges) where it cools and becomes an impervious tunnel lining. In the ground beneath Southern California, such a machine can drill a tunnel at the rate of seven OR MORE miles per DAY! At this speed, the MTA can not only complete subway projects ahead of time and under budget, but the agency can then start to think about adding express lines to the presently existing subway system.
    Of course, there’s the problem with all that heat in a built-up area with utility lines. Heat rises, whether it’s by conduction or convection, and gas lines may suffer adverse conditions during the use of such a machine. Just imagine tunneling through the La Brea Tar Pits with a subterrene (possibly an explosion or worse, who knows?)
    Does such a machine exist? YES, IT DOES!

      • Did you read the arctile that you posted the link to? It would require a vast amount of power. The one that the Soviet’s tested used a nuclear reactor. Don’t you think that might be a problem in LA? Also, what works on a small scale may not work on a large scale. The front surface (thus the material that must be melted and shoved aside, and the power required) goes up with the square of the radius. Also the disposal area goes up only in direct proportion with the radius. This means that as the hole gets bigger much more material needs to get shoved outward.

        • I did not say if it would or would not be cost effective. My point was that most likely such technology most likely would not work with all the variations in soil along the route.

          Assuming it would work, which I doubt, the extra cost in power may be less that the extra time it takes to bore out such a tunnel.

          Los Angeles installed a lot of fiber optic phone lines where the heat could create a problem.

  3. “Yesterday night’s cutterhead arrival, carried on a flatbed truck, was through the Port of Long Beach via ship from Germany, where it was manufactured.”

    This sentence makes my brain hurt.

    • I fully understand that it’s absolutely appalling to some people to see that the United States, as a nation, uses services and products of other nations for assistance in some endeavor. I sometimes find it upsetting that the Los Angeles area must buy rail equipment from nations which know absolutely nothing about the people who must use that equipment. However, the world’s nations are becoming more global in the years to come; all that should really matter is that the quality of the product (or service) is acceptable or better.

  4. First what ever happened to the boring machines that dug Red the Purple Line tunnels? Will the same boring machines be used for the Crenshaw and the extension of the Purple Line, Will they be saved and reused for future planned tunnel sections of new lines?


    • Hi Alan;

      In likelihood, each contractor for the respective projects will use their own tunnel machine. There are also some differences in soil types in the different areas to keep in mind.

      Steve Hymon
      Editor, The Source

      • Thanks Steve, also I forgot to mention the Regional Connector. However the tunnel machines are very expensive and require 2 machines of double the time. can the contractors work together and share some of the machines? Many millions of our tax money could be saved. Did the MTA take this into consideration in their RFQ’s?

        Again thanks


        • Hi Alan;

          The agency has said that the contractors are welcome to work together on the TBMs (if that’s even possible) but I don’t believe it was required in any of the RFPs, which as you know went out separately for each project. The other issue is there are overlapping timelines for the projects.

          Steve Hymon
          Editor, The Source