Reply to post: Re: "it's a [..] electric bus that automatically switches between tunnels and lifts"

Re: "it's a [..] electric bus that automatically switches between tunnels and lifts"

His 14 times quicker could be that he's arguing total building time - in not having to build the complex infrastructure of stations.

Or it could be (and this seems more likely to me) that as his lift-busstop-thingies are shafts drilled down to tunnel level, he could lower tunnelling machines down all of these and dig the tunnels from multiple machines. So it's the sort of idea where if you spend billions on tunnelling machines but have contracts for years ahead, you could use loads to make each contract much quicker and then re-use them on later projects.

I think Crossrail is only using something like 8 machines to dig a very large network. And they finished (and mothballed) a bunch of stations in 2016, so they could move on to the next bunch to finish about the same time as the network. So in principal they could have built the network twice as quickly by using twice the number of machines and employed loads of extra contractors to build all those stations simultaneously. I imagine they decided that added too much risk, as to time and cost over-runs, as well as disrupting the rest of London an unacceptable amount.

People under-estimate the cost of tunnelling though. It's not just having a few machines and crews to run them. You've got to do loads of geology and surveying. If you dig somewhere like London you've got to have a research team to track previous works too - and an archaology team to deal with all the plague pits and Roman remains. Plus time in the schedule to let the archaeologists sit in a trench for a couple of months on an unexpected bit of your site. Plus you need a factory to reprocess all the soil you dig out, and send it somewhere. And a huge amount of concrete infrastucture to line the tunnels - the machine sprays quick-drying concrete on the walls and then lays fitted concrete tiles over the top of that - and you need yet more for soil-grouting (to shore up weak spots and wet-spots).