Open trench, Slurry wall or TBM 2

[let]

We are doing s feasibility study of a steam utility tunnel of about 2000 ft and about 12'x15' wide at 30 ft depth. The tunnel is to be installed on a congested area with buildings and exiwsting utilities close by that do not permit open excavation without shoring. Other constraints include optical lab nearby that require minimizing vibration. Thus, conventional sheet pile shoring (driven piles) is out of the question. We have 70 utilities crisscrosing above the tunnel from 4" dia. to 30" steam lines.
Our dilema is selecting the cheapest method to lay the tunnel. We are condidering pre-drilled pile construction, slurry wall construccion used as shoring (too many existing crossings?) or using Tunnel Boring Machines under all existing utilities(costly?). If anyone has experience with this types of construction I would appreciate your comments or links to proper information. One more option would be to go arial at about 25 ft of the ground with pilons that integrate into the architecture of our site. I could not find any examle were this was done. Was it?

 

[Ginger]

Dear Let

You don't state what material this culvert/tunnel is to be constructed in so my thoughts will be generalisations:-



Andy Machon
Andy@machona.freeserve.co.uk

 

[Ginger]

Let

OOPS !! Here are my generaliations, the figures are very much ball park numbers:-

TBMs: To fit in your proposed culvert you would require a TBM with a cut diameter of about 6.4m diameter or a 5m dia machine to give an equivalent cross-sectional area. For a TBM you can wave goodbye to about £3-4million delivered to site (unless you have one available to hand). You then need to sink launch and reception shafts of at least 14m diameter in order to construct the tunnel (allow (say) £100,000 per shaft) and then (say) £2000/m of tunnel leaves you at around £6.5M A little expensive I think!! You may get a buy-back deal on the TBM? Using a TBM does not exclude you from the problem of settlement. You will get settlement with all forms of tunnelling. Can your structures cope with this?

Shield Tunnelling:- If the ground will allow you could use a shield driven tunnel of the same diameters as above. A shield of these diameters will come in at maybe £300,000? These will be fitted with excavators/ roadheaders etc but shafts and tunnelling costs may be broadly similar

NATM tunnel. If the ground allows you could try the sprayed concrete approach. You would need to contact a specialist in NATM design and construction such as Beton Und Monierbau (Austrian company in Innsbruck but carry out work in the US). Would probably be more cost effective than TBMs/shield tunnels.

Slurry Walls:- I don't have much experience of these but the number of crossings I feel would cause problems along with the problem of supporting the services across the walls.

Sheet Piling:- Could use silent piling methods such as the Still Worker to avoid vibration. Alternatively, how about secant piled walls which will cause less vibration although they will remain a permanent sub-terranean feature. The services can easily be supported over a piled trench and propping can be designed to minimise settlement.

On the face of it, based on the extremely limited info I would probably go with sheet piling or NATM .




Andy Machon
Andy@machona.freeserve.co.uk

 

[jane33]

dear sir

i want to know more regarding these slurry walls
from the geotechnical eng point of view
which give me more detail about the construction and positive and negative view point


regard kaveh

 

[let]

Janee33 thank you for your reply about slurry wall. I have completed my project (my post is from last year (Nov 2 2000). However if you are trying to find more about slurry walls I would recommend to start a new tread in this forum. Explain your situation or be more specific about what are you searching for. Slurry walls are used mostly to construct in heavenly constructued areas, where excavation with conventinal methods is not possible.

 

[JAE]

Andy: great comments. Would agree with your hesitation about slurry walls in a site such as this. Too many utilities would be a detriment to the trenching operations.

I would suggest a strong look at above-ground skywalk instead of trying to weave your way around and through so many obstructions and, at the same time, deal with the sensitivities of the surrounding operations.