I'm in Seattle, and Bertha was digging for about five years. And it's been an incredibly expensive effort, with lots of setbacks and budget overages.
Granted, it's digging a much larger tunnel, and the ground it's digging though is probably different than a stretch of land in LA.
But TBC was whipped up what... a bit more than one year ago? And from scratch, they've already completed a 2 mile tunnel, and I'd be surprised if it was at a cost-per-mile anywhere near what Bertha ran.
The Boring Company bought an off the shelf machine used for sewer lines and dug through a desert at less than a fourth of the maximum depth Bertha did.
That's what perplexes me: what is the innovation behind Boring Company? Nothing? It seems like their main claim to fame is navigating bureaucracy very quickly, but what they are trying to accomplish could have been done years ago.
However digging that tunnel was probably a good idea, as it gives them some operational experience, and also allows them to start work on their underground transportation concept already.
Although I'm not sure if they've actually accomplished anything new yet other than push forward the concept of smaller diameter tunnels.
Here's the 3 high risk factors for Seattle Bertha, from: https://www.bizjournals.com/seattle/news/2014/12/12/mcginn-e...
Technically, he said the machine's diameter, as the largest in the world, warranted a "high" level of risk, a five out of five.
Also rating a high level of risk – a five – was the underground material. Neff wrote what he called the "geologic setting" was "Highly complex, sticky clays, flowing sands, abrasive materials, large boulders."
And third, the high water pressure at the tunnel depths, which seems to be proving a problem now, rated "above average" risk at a four.
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This is not to try and take something away from TBC - they may be making very good choices (2 smaller bore tunnels than 1 big one? Better locations?) who knows, but it's just not apples to apples.
Well, "normal" small diameter TBM's in "normal" terrain/rock can go as fast as 400 m/month ("net" progress rate) to this you add some time for preparation and assembling of the machine (and some time for disassembling after the actual bore is finished), a good "average" is 240-280 m/month.
To be fair both the Seattle and the Hawthorne projects are way shorter than what a TBM is usually used for (i.e. preparation/assembling has a larger weight on project times).
If the "boring Company" started it in January 2017 and will end it in December 2018 it is 3200 m in 23 months, i.e. 140 m/month (including the assembling/preparation), not particularly impressive.
Bertha is another story, it is "huge", 17.4 m in diameter, the Hawthorne project TBM (called "Godot") is only a 4.2 m one (around the minimal size of TBM), it helps to compare the cross section area, 8.7^2xPi=237 sqm, 2.1^2xPi=13.9 sqm.
In any case the Seattle project is (in)famous for the steel pipe that allegedly broke Bertha's main bearings sealings, once it was repaired it dig quite fast, after all (and given its size), 2830-330=2500 m in 15 months is roughly 170 m/month.
