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[quote user="CMStPnP"]What I find highly irresponsible of this entire project is that it was approved with no real working proof of concept. [/quote] I agree. And even the concept seems quite different from what he proposes regarding tunneling. Vision video: <a href="https://vimeo.com/259707751">https://vimeo.com/259707751</a> I don't see how this fits with "proof of process" tunnel The Boring Company is building LA with 12 ft inner diameter. According to The Guardian the Tesla Models S and X won't fit: <a href="https://www.theguardian.com/technology/2018/may/09/elon-musk-the-boring-company-tunnels-dont-fit-tesla">https://www.theguardian.com/technology/2018/may/09/elon-musk-the-boring-company-tunnels-dont-fit-tesla</a> I'm still looking for tunnels that cost 1 billion per tunnel mile outside New York. I found a few but the costs are misleading. The given cost are for complete projects mostly including two tunnels and a number of station. So how expensive is a mile of tunnel really and why. I found the Portland OR CSO tunnels. The 3.5 mile, 14' i.d./16.5 o.d West tunnel cost $278 million to build including a pump station: <a href="https://www.tunneltalk.com/Portland-CSO-Sep11-Sewer-Project-shortlisted-for-award.php">https://www.tunneltalk.com/Portland-CSO-Sep11-Sewer-Project-shortlisted-for-award.php</a> That is $80 million per mile in demanding geology. When I look at the reference page of Herrenknecht, the German TBM manufacturer, for tunnels in soft soil below 17' o.d., I get the feeling that The Boring Company is considering to re-invent the wheel. <a href="https://www.herrenknecht.com/en/references/references-tunnelling.html#geology=1&diameterMax=5250">https://www.herrenknecht.com/en/references/references-tunnelling.html#geology=1&diameterMax=5250</a> If you are interested in details of different types of TBM the Herrenknecht website has them: <a href="https://www.herrenknecht.com/en/products/core-products/tunnelling/single-shield-tbm.html">https://www.herrenknecht.com/en/products/core-products/tunnelling/single-shield-tbm.html</a> Each type contains a rendering that can be zoomed in and then describes the important parts of the TBM. If it were so easy to increase power to speed up the boring. The geology determines how fast you can bore without consequences at the surface. In soft soil one needs to grout the gap between shield and the smaller diameter liner. Curing takes some time. In hard rock you need a minimum pressure to destroy the rock, but on the other hand not much ore you have to exchange the cutting wheels too often. And you need to power wedge the TBM into the excavated tunnel so it can apply pressure on the cutterhead. This process might light the propelling force. For me it seems unlikely that The Boring Company can accelerate to 14 times today speed as told on their website. Tunneling 17' o.d. is already in the ballpark of one tenth of the lamented $1 billion/mile. Sounds like a lot of air. But it is Elon Musk so we'll have to wait and see. Regards, Volker
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