Temporary retaining for deep excavation for padestrian underpass

[neaveyoung]

We have one project which need excavation for padestrian underpass. The underpass is below the road level about 20 meter and the length of the underpass is about 15m. So i'm thinking to use sheet piles to drive in and then strut with king post. i'm estimated the driven will need about 40m from the existing road level so that after excavation max.20 meter it will still have about 20 meter penetrate inside the soil.(let said).
So im thinking sheet pile is suitable for this case? Appreciate your suggestion.

 

[JedClampett]

This sounds like a challenging shoring project. There's many shoring methods available in addition to sheet piles, such as soil nails and shotcrete, piles and waling, etc. Sheet piles might or might not be the way to go, although 20 meters seems way beyond its normal use. You need to talk to someone who's done this locally before.
By its temporary nature, shoring is designed to minimal factors of safety, yet you can't afford to have it fail. Normally shoring is written into the contract as a performance item, giving the GC a lot of leeway in its design. Basically, it's a means and methods item, where you don't care how its done as long as it meets certain parameters.

 

[Qshake]

I can't say I've ever seen a shoring in soil of 20m. In water/riverbeds, yes, pure soil no.

As JedClampett notes this depth seems beyond routine use of sheet pile.

Perhaps a solider pile /lagging application is best.

And on second reading, it seems like you need to go down 20m and then say burrow under the road? Thereby keeping the road open?

Another option may be to use tunnel liners, ring beams, or, again, solider piles. The liners can be used in a vertical application (shafts) as well as a horizontal application (tunnels).

See this link for examples:

http://www.bortunco.com/index.html

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[BigH]

One big ticket item is how to keep the road open - might wish, if you have room to develop an outside lane - thereby keeping two lane traffic - work on one half; then reverse it for the other half. You might want to check out shorings in Singapore. They will dig a large bentonite slurry diaphragm wall and use cast in place beams across the top (deep ones) to maintain the top from deflecting too much. Very successful. This technique is found in the proceedings of the 2007 and 2009 Underground Singapore Conferences at the National University of Singapore (NUS). Might be able to get copies of relevant papers from a prof at NUS.

 

[neaveyoung]

Thanks all.
BigH, Do you have a copy of NUS conference? Appreciate if you can share it with me. Thanks.

 

[dicksewerrat]

Are the approaches to this underpass already existing? If so, why not look at a pipe jacking or tunneling process. Leave the road open and work from the sides

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[irawanfirmansyah]

Iam sure sheetpile is not appropriate for such deep excavation. You can use either soldier piles (if ground water is deep) or secant piles / diaphragm wall (if ground water is high).
For supporting the wall you can either use concrete slabs with kingpost (top-down construction method) or permanent ground anchors / wall to wall steel struts (conventional bottom-up construction method).
Normal vertical spacing for ground anchors/wall to wall struts is about 3 -4 m, whereas for concrete slabs is about 6 m.
I can't comment on penetration depth since no boring log available.

 

[BigH]

Yes, I have - I'll see if I can post it - might take a few days . . .

 

[dcarr82775]

I've done 55' deep cuts which is pretty close to 20m using soldier beams/lagging/tiebacks or struts. Unless water is a problem slurry walls are normally to costly. If it is just a pedestrian crossing it can't be all that wide so a couple levels of wales and struts instead of tiebacks seem like a good way to go.

I would think given the depth and length tunneling might be the easiest way to go.

Out of curiosity, are there access stairs at each end? I am having trouble visualizing the condition where a 15m long tunnel is located 20m under ground.

 

[neaveyoung]

After i have read all your comments. I think my case is suitable for soldier pile with sheet pile lagging. But im wonder how the sheet pile lagging can be done... because i honestly said im fresh in temporary retaining. Have anybody have the sequence / method of work?
for dcarr82775, there should be access at the end but this is only a preliminary concept/method to be use so this will not a main issue.
The width of the underpass pedestrian is about 4meter plus so i think only useing wall strut is sufficient.
Due to this is not a very long tunnel so we are not consider for the pipe jacking or use TBM for safe cost purpose.

 

[DRC1]

The feasibility of sheet piling depends on the soil profile. 20m will require a driving template. You can do a king pile system. The most common way to integrate H-piles and sheet piles are jokers. These are connectors that are welded to the H-piles. The allow the H-pile to receive the sheets. Bracing can work and in such tight space may be only practical means, but for such a deep cut earth anchors are more reliable. Embedment below 10 meters does little good, and since the dam is being braced, such penetration will not provide any advantage. Provide enough penetration to support the dam during bracing . to support the excavation below the last row of bracing, and to prevent any blow of the bottom.

 

[csd72]

neaveyoung,

You give no information with rregards to what the permanent structure is going to look like.

I would expect that using something more permanent like diaphragm walls to also act as the temporary shoring may be a better solution.

 

[PEinc]

In most instances, diaphragm walls are a last resort, especially for a small project (like a pedestrian underpass?).

http://www.PeirceEngineering.com