Tunnel Boring vs Cut and Cover....

[Anonymous]

Drove thru Cleveland yesterday and was surpised to learn that the bus rapid transit project is as disruptive as diging a subway. Utilities have to be moved and lots of digging.

Which means that perhaps Cleveland should have just gone along with the Subway between Cleveland and University Heights years ago(As planned) and used a tunnel boring machine deep under the streets and that way they would not have to have to move the utlities. 

[CSSHEGEWISCH]

By Tunnel boring, I will assume that you mean shield tunneling, as was used on the first St. Clair tunnel.  To avoid disrupting utilities, including sewers, you would have to go very deep, anything over 40 feet below ground level would not be practicable because of the long staircases needed for access to stations.

Since Cleveland is using cut-and-cover, I will assume that the topography is similar to Chicago, with water-bearing soil and blue clay.  I would bet that the shoring along the walls of the trench is very heavy and a lot of pumps are in use to keep the water out.  While a tunnel shield could also be used (the State and Dearborn subways in Chicago were both done this way), it would require the use of compressed air and airlocks to keep the water out.  This leads to well-known health risks to workers such as the bends and the pay scale for working in compressed air is also higher.

[carnej1]

 Generally "tunnel boring" refers to the use of a tunnel boring machine rather than a shield....I have no idea about relative costs though I'd imagine cut and cover is cheaper but can't be done in many built up areas...

[ChuckCobleigh]

Boring machines used on the LA subway from downtown to the San Fernando Valley, largely to reduce disruption but also to go under the HWood Hills near Cahuenga Pass.

[rrnut282]

 Generally "tunnel boring" refers to the use of a tunnel boring machine rather than a shield....I have no idea about relative costs though I'd imagine cut and cover is cheaper but can't be done in many built up areas...

Cut and cover was used on many subway systems in many urban, downtown, and built-up areas.  For example, many early lines in New York City and most of the Washington Metro subway was built using cut/fill and these are just the ones I know about living here in the flatlands.  I'm sure there are many other examples.

You don't necessarily have to move existing utilities out of the way to use cut/cover methods.  I've used H-beams laid across a trench with the utility line strapped to the beam so it can hang in mid-air until the backfill covers it up again.  I saw someone try this with clay sewer pipe with less than stellar results.

[Simon Reed]

Unless you're VERY deep, or in very porous strata shields are'nt used too much these days.

This busway. Is it going underground? Frankly unless I'm somehow lost in US/UK translation I can't imagine a busway requiring deep level boring.

Are we possibly talking about a guided busway here - eg Los Angeles, with bus lanes along the median strip of freeways?

A deep level busway will require some pretty heavy duty ventilation. 

  

  

[Anonymous]

Here in Dallas, we have a tunnel that our light rail trains run thru, it is roufly 2 or 3 miles long if not more.  I was told that they tug the tunnel by hand since the tunnel boring machines are so exspencive.  I know the station in the tunnel is down 10 stories.  It has eleveators that go up at an angle, along with regulat stair cases, and escualtors. 

[jeaton]

Tunnel boring machines are extremely expensive to own or lease and operate, so it simply depends on the economics.  They have an advantage when cutting a bore through solid rock because drilling, blasting and triming any resulting loose rock is eliminated.  Further, the machine leaves a bore with a consistant dimension which allows the use of prefabricated lining with a minimum of grouting.   

Typically, cut and cover will be more practical when when the top of the tunnel is at or fairly near ground level.  For one thing, excavation of unconsolidated material is relatively easy with shovel machines.  It is also possible to deal with existing underground utility lines as the digging can work around such lines and leave them open for subsequent relocation.  In such circumstances, a TBM would have to be pulled back from the face and small machines would have to be brought forward and work with manpower to clear the space around the line and then the line would have to be relocated before the TBM could go back to work.  An idle TBM will chew up dollars even faster than it will chew up rock.

I recall reading that a TBM is working somewhere in Europe where the bore depth is shallow and the material is unconsolidated.  It has extra panels designed to support the tunnel walls and ceiling until the liners are set in.  Extra features equal extra cost.  

By the way, I understand that a TBM is being installed to cut the new tunnel between Penn Station and Grand Central.  I believe that the bedrock at that location on Manhattan Island is very close to the surface so there a TBM makes sense.       

[JT22CW]

By the way, I understand that a TBM is being installed to cut the new tunnel between Penn Station and Grand Central

Where?  There is no tunnel being built between NYP and GCT at all.  That was a "wish list" proposal on the Access To The Region's Core website, a proposal that has been defunct since 2003, since the New York MTA withdrew from the project.

The only remaining Access to the Region's Core project that proposes tunneling is the new set of tunnels under Bergen Hill and the Hudson River, parallelling the Pennsylvania Railroad's North River Tunnels, and their new ephemeral "34th Street Station" which is proposed to be built somewhere under Macy's (itself a scaled-down and aberrant version of their old Alternative P).  It is proposed to use a TBM for that excavation.  This project is not fully funded at all as yet (they're looking for close to $8 billion for it, right now); therefore, nothing is being installed at present.

[jeaton]

By the way, I understand that a TBM is being installed to cut the new tunnel between Penn Station and Grand Central

Where?  There is no tunnel being built between NYP and GCT at all.  That was a "wish list" proposal on the Access To The Region's Core website, a proposal that has been defunct since 2003, since the New York MTA withdrew from the project.

The only remaining Access to the Region's Core project that proposes tunneling is the new set of tunnels under Bergen Hill and the Hudson River, parallelling the Pennsylvania Railroad's North River Tunnels, and their new ephemeral "34th Street Station" which is proposed to be built somewhere under Macy's (itself a scaled-down and aberrant version of their old Alternative P).  It is proposed to use a TBM for that excavation.  This project is not fully funded at all as yet (they're looking for close to $8 billion for it, right now); therefore, nothing is being installed at present.

Sorry, I was wrong about it being a Penn Station/Grand Central.

The project I saw is described here: http://www.nationalcorridors.org/df2/df06182007.shtml#Tunnel

Since I am not versed on the details of New York City's geography, I don't know how this matches up with the project you speak of.

 

[JT22CW]

That's a different project…the Long Island RR's East Side Access, which has been in progress (under construction) for a while now.

The intent is to use the lower level of the existing 63rd Street Tunnel (upper level is in use for subway trains) to bring the LIRR into a new level of Grand Central Terminal (they cannot use the former New York Central/current Metro-North tracks and platforms since the third-rail types are incompatible).  It does not involve tunneling between Penn Station and Grand Central.  (The only project that refers to a tunnel between NYP and GCT is in the first link of my previous post.)

The capital costs of that project (ESA) have run into multiple billions, even with using the existing tunnel.  And it won't result in additional platform slots for NJ Transit or Amtrak at Penn Station, since LIRR is holding on to those for possible new trips into Manhattan anyhow (it'd be amazing if they extended West Hempstead Branch trains into Manhattan, that being a lower-frequency electrified branch).

[Anonymous]

 The Busway still required huge amounts of money to move utlities...

I am arguing that if we had built a tunnel bored subway that we would not have spend as much money

[tomikawaTT]

By the way, I understand that a TBM is being installed to cut the new tunnel between Penn Station and Grand Central

Where?  There is no tunnel being built between NYP and GCT at all.  That was a "wish list" proposal on the Access To The Region's Core website, a proposal that has been defunct since 2003, since the New York MTA withdrew from the project.

There is one TBM working under New York City, but it's digging an aqueduct, not a rail tunnel.  IIRC, it was one formerly used to drill the pilot/access portion of the Chunnel.

What tunneling method is being proposed for the "Deep under Grand Central" platforms/tracks intended for the LIRR - or is that dead, too?

Chuck (ex-native New Yorker, 3000 miles removed)

[Suburban Station]

For whatit's worth, there are other reasons to use TBM. Poltically, it's less disruptive to those on the proposed route and thus more politically acceptable. Economically, frequently the cost to the community of using cut and cover is not accounted for. In Philadelphia they are reconstructing the elevated. It's less disrputive than cut and cover but some 3/4's of the businesses along the route have gone bankrupt since the reconstructon began. Using a TBM is less disrupive in this sense, bringing chaos only to station areas. I watched a special on the building of the Athens subway that was pretty interesting. Because it doubled as a massive archaelogical dig they had to bring in a mini-boring machines. they are also building a metro line in naples Italy and I believe they are using a TBM.