Despite TBMs being used all the time it is genererally much cheaper to build a tunnel by cut and cover - that is just call in excovators and dig a hole then cover it. when an excavator breaks you push it aside and get another until it is fixed. Want to go faster - just hire more excavators the overall cost is the same since you are done faster.
tbms are cheaper if you must go deep, but deep is a negative for subways since people must get down which takes time (faster is always better).
It is claimed that cut and cover is toa much surface disruption - but cut and cover is much faster and so the disruption to any one place can be quick enough. Better to manage disruption than eliminate it.
when a tbm breaks your project is delayed while you wait for parts and then fix it in place.
Tbms do go under everything else, but experience proves you can find things and go around them quick enough (sometimes there is a delay as somethingeof archeological interest is found - but evperience shows this is still cheaper than a TBM.
Yes TBMs are cool and useful but the simple shoud not be over looked
tbms are cheaper if you must go deep, but deep is a negative for subways since people must get down which takes time (faster is always better).
It is claimed that cut and cover is toa much surface disruption - but cut and cover is much faster and so the disruption to any one place can be quick enough. Better to manage disruption than eliminate it.
when a tbm breaks your project is delayed while you wait for parts and then fix it in place.
Tbms do go under everything else, but experience proves you can find things and go around them quick enough (sometimes there is a delay as somethingeof archeological interest is found - but evperience shows this is still cheaper than a TBM.
Yes TBMs are cool and useful but the simple shoud not be over looked