12 m depp excavation

[killswitchengage]

Hello , i would like your help for the support of a 12 m deep excavation in urban area. The soil layers from top to bottom consist of :
1) 3 m fill ( with construction debris ) .
2) 2.5 m Sandy silt with gravel .
3) 0.5 m mollasse ( its a local French term here )
4) 2 m marly clay
5) Marl til the end of the borehole at 20 m.

The site is fairly small and the geological layers reminds the same , since there are 4 underground parking lot the total excavation depth will (4x3m = 12) we add to it 0.5 m for the raft foundation. Our piezometers detected water at 3 m in summer time , now we are thinking of using Berlin or Paris type walls for the support of the excavation as no company in my country work with slurry walls. Thing is i am currently inexperienced for this kinds of foundations same thing cause with the tiebacks that we should use too .

My question is can we use Berlin or Paris type walls in this case ? I can assume that there will be no water flow from under the walls ( marl ) .
Also what are the typical stiffness values for tiebacks ?

 

[Retrograde]

I have never heard of a "Berlin" or "Paris" type wall. Maybe post some pictures/sketches.

 

[killswitchengage]

its basically soldier pile wall with the pile either made of RC round column or wide flange H beams i guess

 

[SlideRuleEra]

Since ground water will be an issue, could you consider a braced, driven sheet pile cofferdam?

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[hokie66]

If not slurry walls, what about secant pile walls? That way, you could perhaps use upside down construction.

 

[Retrograde]

I would think a soldier pile wall would not be a good option given you have the water table at 3m depth and the top 5m of your profile are fill and silts. The excavation will fill up with water.

I agree with hokie66 that a secant pile wall would be a good option.

 

[killswitchengage]

like i said they will put the building on raft foundation so no braced excavation, so i guess secant piles is the way to go.

 

[jayrod12]

You could still do a braced excavation. I've seen them done with both slabs and walls poured around the braces, and then the holes filled in after the fact.

 

[killswitchengage]

@jayrod12 could you give me an real ex ?

guys if a soldier beam wall is constructed according to standards and knowing that the marl underneath the wall is impermeable of course , i think there will be no seepage water toward the excavation

 

[jayrod12]

I'm not sure what you're looking for in terms of real examples. They form and reinforce the walls and slabs around the rakers. then one the walls and slabs have reached their design strength and the shoring is free to be removed, they go and cut the rakers and then infill the holes in walls and slabs.

The design methodology is no different than designing for openings in wall and slabs to begin with. The formwork and reinforcing aspect is slightly more difficult from a labour perspective but still manageable.

 

[PEinc]

If the marl is at a lower stratum, there could be (will be) seepage, from the upper, more pervious soils, across the top of the marl.

http://www.PeirceEngineering.com

 

[killswitchengage]

PEinc the wall gets all the way more than 8 m into the marl so no seepage is expected

 

[Guest262653]

If you use a soldier pile wall, what do you think that will happen to the face of your excavation when you dig below the ground water level?

 

[PEinc]

killswitch, I am talking about seepage of water over the top of the marl and through the lagging.
You will need to dewater the perimeter or you will need to use steel sheet piling to retain the water. You have to determine if steel sheet piling can be driven through the cohesive soils to the required depth below subgrade.

http://www.PeirceEngineering.com

 

[BigH]

One question that hasn't been addressed . . . are there adjacent buildings on the property line - or close to it?? Whatever method you use, it will have to be robust enough to prevent damage to adjacent structures.

 

[killswitchengage]

yep there are adjacent buildings as i said and the worst part they are made of old masonry.

@PEinc : how can i judge the ability to penetrate the cohesive soil using sheet piling

 

[chicopee]

Whatever method you use, do a survey of nearby structures (iside and outside) to insure that vibration damage claims are kept under check.

 

[BigHarvey]

You can't use a berlin wall if you have water behind. If your site is small go for a secant pile wall which require less space.

 

[PEinc]

how can i judge the ability to penetrate the cohesive soil using sheet piling"
You could do some reading about pile hammer selection, talk to a local pile driving contractor, and talk to an equipment supplier that rents pile driving equipment. You will need to show the contractor and supplier the soil borings/geotech report.

http://www.PeirceEngineering.com

 

[killswitchengage]

ok again thank you guys
We did conduct DCPT tests that showed for the most part a max depth of 12 m