Slashdot Mirror
Elon Musk Unveils 1.14-Mile Boring Company Tunnel (cnbc.com)
Last night, Elon Musk unveiled his vision of a high-speed tunnel system he believes could ease congestion and revolutionize how millions of commuters get around cities. CNBC reports: Musk, who founded the Boring Co. two years ago after complaining that traffic in Los Angeles was driving him "nuts," says the demonstration tunnel cost approximately $10 million to complete. Engineers and workers have been boring the 1.14-mile-long tunnel underneath one of the main streets in Hawthorne, California. One end of the tunnel starts in a parking lot owned by Musk's Space X. The other end of the demonstration tunnel is in a neighborhood about a mile away in Hawthorne.
Tuesday afternoon, the Boring Co. gave reporters demonstration rides through the tunnel in modified Tesla Model X SUVs, going between 40 and 50 miles per hour. Engineers have attached deployable alignment wheels to the two front wheels of the Model X. Those alignment wheels stick out to the side of the main wheels and act as a bumper along the track walls inside the tunnel, keeping the Model X on course and preventing the vehicle from running into the side walls of the tunnel. While the Boring Co.'s first tunnel may be complete, it is far from being finished. The surfaces are bumpy and have yet to be smoothed out. As a result, the demonstration ride, for now, is rough and passengers in the Model X definitely feel the alignment wheels bumping into the track walls to keep the SUV on course.
Tuesday afternoon, the Boring Co. gave reporters demonstration rides through the tunnel in modified Tesla Model X SUVs, going between 40 and 50 miles per hour. Engineers have attached deployable alignment wheels to the two front wheels of the Model X. Those alignment wheels stick out to the side of the main wheels and act as a bumper along the track walls inside the tunnel, keeping the Model X on course and preventing the vehicle from running into the side walls of the tunnel. While the Boring Co.'s first tunnel may be complete, it is far from being finished. The surfaces are bumpy and have yet to be smoothed out. As a result, the demonstration ride, for now, is rough and passengers in the Model X definitely feel the alignment wheels bumping into the track walls to keep the SUV on course.
If you're building a tunnel, laying a set of rails and an electric rail is a relatively small cost compared to the tunnel itself. The vehicles should run on rails -- metal-to-metal friction is lower than rubber to concrete, and they provide a way of powering vehicles without dealing with toxic batteries.
I'm not suggesting building a conventional subway, but rather some form of personal rapid transit. Designed correctly, the vehicles could "switch" themselves to different tracks without needing the complex switching equipment used by trains and subways today.
He only drives down costs by cutting corners. His current tunnel lacks
If and when Elon constructs an actual transit tunnel he would have to follow NFPA 130 (TBC is currently advertising a position for a life and safety officer knowledgeable in NFPA 130 on their website) This code details a number of required safety features. The tunnel must have automated fire detection and sprinkler systems, the ventilation system must be sized large enough to quickly extract smoke. You need to have an emergency walkway of a minimum width and clear of obstructions. You need to have egress points at regular intervals either to another tunnel or to the surface. These egress points need to be shielded by fire rated doors. You need to have emergency lighting. You need to have standpipes for firefighters to connect their hoses too. Etc. etc.
Oh and this tunnel was neither dug faster nor cheaper than any other tunnel.
For a better comparison Super Excavators (the previous owners of Godot) used the exact same machine to build a 1,640 ft sewer overflow tunnel for $12.4 million, or scaling up $38 million/mile, right up there with Elon's $40 million cost, and the contract had profit factored into it as well and was done in a more challenging geology and included digging deeper access shafts that what Elon did. So I guess the Proof of Concept is that Elon can spend more money digging a tunnel using the exact same machine at a shallower depth and easier ground than an existing tunneling contractor.
.
Unlike Spacex and Tesla, it has been clear from the earliest press releases that this tunnel business doesn't really have much to do with scientific innovation or invention. All Elon Musk realized is that he might be able to make money off of something which has been a bit of an open secret for the last ten years at least - that urban taxpayers were paying literally billions of dollars for short subway expansions (the Second Avenue Subway in New York being the biggest example), when there is absolutely no reason it couldn't be done for orders of magnitude less money. It's a combination of insane over-engineering (why the hell would you spend a half a billion dollars to climate control three subway stations in a subway system with over 200 un-climate-controlled stations, for example) and massive corruption. The tunnel boring machine used to dig the Second Avenue Subway required 5 to 10 people to operate. The city paid 50 to 60 people. There are pictures of them all standing around. Musk probably thinks he can write some simple software and do it with one dude. And he's right. Musks ten million dollar one mile tunnel is basically a giant "ha ha suckers" to the people (me included) who financed a 4 billion dollar one mile tunnel in Manhattan. Some city is going to give him a contract, and he's going to deliver, because it should never have cost 4 billion dollars to put a train in a tunnel to begin with.
A/C was the least of it -- why did the (two-track) 2nd Ave Subway stations need to have a full concourse level rather than just a narrow "bridge" to cross the tracks?
However, there were problems other than corruption. NYC is built on bedrock, which is a bitch to dig through. And it's a much older city than L.A., so there are poorly-market utility lines and other infrastructure underground -- half the battle was locating this stuff and moving it, as well as avoiding damaging the foundations of buildings.
As far as the tunnel-boring machine, was this thing running 24/7? There are 168 hours in a week -- with 40 hour weeks and vacation time, 5 crews sound about right. Add some support staff for repairs and the like, and you have your 50 people.
The vehicles should run on rails -- metal-to-metal friction is lower than rubber to concrete, and they provide a way of powering vehicles without dealing with toxic batteries.
LOL at "toxic batteries" - you aren't going to be eating them and the material inside get recycled.
As for rails - the reason not to use them is that laying them down is a lot more exacting. It adds a lot of needless delay to building out the tunnels, a lot of maintenance in the tunnels to make sure they stay aligned exactly. Not using tracks means maintenance is mostly moved outside the tunnels, meaning fewer closures or delays (I have seen a LOT of issues with subway rails over the years, and I don't even live in a place with a subway system!).
I am also not sure the cost will be relatively small compared to tunnel cost by the time they have advanced the tunneling machines - even V1 of the tunnel was just $10 million for 1.3 miles. They are talking about making something like 10-30 tunnels between various locations, that is a hell of a lot of track.
"There is more worth loving than we have strength to love." - Brian Jay Stanley
Because he isn't a very smart man
Fixed that for you. Here’s what a real tunnel engineer has to say about this.
So really rather disappointed in the presentation and Elon still seems fairly ignorant on some pretty major obstacles when it comes to tunneling.
First thing I want to point out is that when Elon was touting the fact that tunnels are immune to to the effects of weather he completely ignored the threat of flooding for tunnels which is a serious issue. Look at NYC tunnels in the aftermath of Sandy for proof of that, and many of those tunnels had fairly extensive drainage systems and still flooded.
Also a major issue with his plan to reuse "dirt" from onsite to create concrete liner segments is that not all aggregate material is suitable for use in concrete. A major limiting factor is that the aggregate needs to contain very little if any silica to avoid reacting with the alkali cement and forming a expansive chemical gel. You also can't have any pyrite present in the aggregate for the same reason you want to avoid silica, and you want avoid expansive shale as well. Then there is the fact that a lot of material is simply lacking the UCS strength to be a suitable aggregate for concrete, clays, mica, mudstone, etc are all to weak for use and fairly common.
On to the TBM itself, I'm assuming all comparisons where against Godot in terms of things such as power output. Elon talked about increasing the power of the machine by 3x, we know from the published spec sheet that Godot which is a Lovat tbm built in 2005 has 1400 hp, 3x that gets you to 4200 hp, for comparison Bertha which recently finished tunneling a road tunnel in Seatle boasted 25,000 hp. More to the point though is that increasing cutterhead speed isn't a universal solution. In soft ground with a closed face machine, like what Elon has encountered so far, you want a faster cutting head as it is primarily being used for soil mixing and you don't need very much torque. However, in hard rock or in an open face machine you typically want a lower speed cutterhead with higher torque so you can shift and clear the muck. And in mixed face conditions you want a slower cutterhead speed down to reduce shock loading on your cutting tools as you constantly go between soft and hard ground. The Robbins Company has published white papers on how they've found that slowing cutterhead rotation dramatically increase cutting tool life, decreases downtime for maintenance, and increases overall productivity.
Also Linestorm appears to have considerably larger openings in its face shield which works great for soft ground with no rock in it. However, the gamble you take when you run large openings like that is that you can ingest oversized boulders which will either clog or damage your screw conveyor which is you'll only see contractors run that sort of wide open face when they are absolutely certain they won't encounter any boulders or rock features along the way.
Lastly, Elon talked about how average subway speeds aren't that fast but I feel like he is massively underestimating the throughput capacity of subway systems, For example NYC's Times Square subway station sees an average of 179,000 passengers per day. Assuming TBC deploys their 16 person pods they've proposed and everyone of those pods is filled to capacity, that represents more than 11,000 pod stops in a location per day, or a pod using the station every 7 seconds, 24 hours a day, that's assuming you have the exact same demand at 11:30PM as you do at 5:00PM on the way home from work
History will remember Musk as one of our generation's greatest inventors. And yet we're doing everything we can to shoot him down: https://www.entrepreneur.com/a...