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baybal2

When the cost of machinery is a rounding error in the cost of the entire project...

Yeah, I don't like that thinking.

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Why not? It just means that the main expenses of the project are labour, materials, energy, etc.

I don’t imagine the paint for the Sistine Chapel ceiling cost much compared with the cost of painting it.

If recovered, the cost of the machine would likely repay the recovery operation many times over even if scrapped.

What I don't like is the thinking of people who rush for the sign off, and paycheck date.

Wear and tear on complex machines is killer. It shows up in an onslaught of tough to diagnose and expensive to solve issues at the end of operational life. The borers are probably engineered for an operational lifetime only a safety factor longer than the tunnel they will dig.

The cost of those machines failing or worse getting stuck is enormous, they have very specific life span and are pretty much discarded even mid project if they dug past their mileage.

These machines are also custom built for the diameter, soil type and probably a plethora of other variables so it’s unlikely that you could reuse them.

They are also not built to be recovered and reused from what I gather which complicates things further.

Hmmm, doesn't seem so at all

Doesn’t seem what?

Doesn't seem real.

What's there to break? The cutters on the face of the TBM, and bearings would likely be replaced few times during boring. Aside from that, what's there to break? Hydraulics is sure to outlast even the longest boring.

Pumps, gearing, sealing, etc should all be easily replaceable.

There have been plenty to cases where these things have broken down which caused years of delays and usually another tunnel had to be dug to get them free, sometimes they changed the path of the original tunnel to circumvent them where it was possible and more cost effective.

These machines are constantly serviced and aren’t operated one minute past their life spans.

I really don’t think you understand how many hours these things operate for....

To put things into perspective machines have a single digit meters per hours top speed and not high single digits to boot, and if you are digging in rock you are looking at sub meter per hour figures.

If you have a source to contradict this I’ll be happy to read it but honestly every source from articles to documentaries pretty much paints the same picture these machines aren’t worth their weight in scrap once they are done with.

If it's not causing pollution from leaks or whatever and it's effectively worn out then you could view it as being as good a place as any to store something that someone could later salvage for its scrap value. I remember someone saying similar about plastics (I think). That if we just stored those plastics we can't effectively recycle until such time as it is possible, it would be a greener solution than e.g. incineration

Breaking big rocks into smaller rocks and then carting them out of a tunnel is already very expensive. It is better that the cost of the machine isn't important.

I saw in a paper that gave reasons tunneling projects were expensive listed labor as a larger fraction than you would think. Consider cars. Your $30,000 car probably costs $60,000 to operate over it's life. Likely more. Not surprise me if tunneling is the same. Operating costs dominate.

Then consider the Bertha problems in Seattle. Two year delay because they needed to dig a rescue pit to get at it after it broke down. Ask would you want to start a tunnel project with an 'used' TBM? Likely not.

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