Sheet pile retaining walls

[dougsmart]

I am designing 25 metre high anchored sheet pile retaining walls. This high is well beyond the range that both the Australian AS 4678)and British BS8002)retaining wall design guidelines say they cover(up to 15 m).The walls are in a marine environment and are founded in very stiff clay. Any suggestions of particular design issues that may arise that are not covered by the codes of practice. Analysis is being carried out using Geosolve WALLAP retaining wall design program.

 

[civilperson]

What steel section of piles are you proposing? Is this combined with soil anchors, tie backs or counterforts of some nature? 25 meters of height will cause significant settlement on the retained side of the piling. Some soil details please.

 

[PEinc]

Is the wall a fill wall (i.e., with embankment being placed behind the wall) or is the wall being built in a cut situation (where you will excavate down for 25 meters in front of the wall)?

 

[dougsmart]

The sheet piles will probably be HZ king piles driven on shore to full depth about 33 down, sheet pile dead man anchors with tie rods at MSL installed and then excavation down 24 metres to form a dredged pocket for a shiplift. Very stiff clay from 12 metres down.

 

[PEinc]

The deadman tie rods will be large and very long. Have you considered using drilled and grouted tieback anchors? I can't imagine a sheet pile wall 25 meters high with only one tier of support. I'd be surprised if you can find a sheet pile wall system strong enough. More details please?

 

[DRC1]

25 meters is a bigwall esp. w/ one level of support. This one definately calls for outside review before it goes out the door. I agree with PEInc. Other things to consider is extensive lab testing. Things you need to know before design: Clay strength at different depths will be
different.
Both drained & Undraind testing
Sensitivity and remoled strength
Consolidation
sand seems or varves
local knoweledg
On some overly consolidated clays they can actually expeienc a loss of strength as it drainsdrain

 

[dougsmart]

The design is being subject to independent review. So far 3 groups have looked at it and all have come up with reasonably similar designs. We have in-put from very experienced geotechnical engineers familiar with the site conditions as I am. We have allowed for changes in the soil parameters on the passive side for the unloaded condition after excavation and for the the long term effects. The real issue is compliance. The design will be subject to independent verification but we do not a code of practice which covers such high walls.

 

[PEinc]

I'm not aware of any special code for higher retaining walls.

 

[VAD]

I would presume that the anchor sheet piles are driven to 33 m as well for this system to function adequately. In effect this would reduce or increase the lateral pressures against the sheeting closest to the excavation. Increase if the system is designed as a double wall cofferdam. I am guessing here in the absense of further details.

If otherwise then one level of tiebacks would hardly be sufficient but if three sets of reviewers have okayed design, then they woyuld have taken concerns into consideration should be okay.

Basal heave my be a problem that needs to be checked through swelling. Seepage via fissures in the stiff clay could occur and this has to be of concern to basal stability. Stiffness of sections used etc

Some additional info would help. As information that may be reviewed, a couple of articles may be of assistance which you probably have used already. These are:

The design of and construction of Sheet-Piled Cofferdams by B.P Williams and D. Waite CIRIA special Publication 95.1993 Provides some detailed eworked examples. The other is Proceedings of the Conference on design and Installation of Pile Foundations and Cellular Structures which is referenced in first textby Fang H.Y and Dismuke T.D Proc Conference Lehigh University USA, 1970, Enviro Publishing Co. Inc

 

[GBTDS]

Another option which I have seen in Japan, Korea and parts of Scandinavia is the use of interlocking pipe piles.
Often less expensive pound for pound, pipe is used with fabricated interlocks typically consisting of a smaller pipe with a slot cut in it and a "Tee" which is a small wideflange cut in half.
The section modulus of a pipe can be huge and adjusted according to the diameter of the pipe and the wall thickness.
Also, for the company installing the retaining wall driving sheet piles 25m (or in this case more than 25m) is not easy especially in stiff clays as you describe. The open pipes with the interlocks acting as "fins" drive very straight and are less problematic in my eyes.
They can also be filled with concrete or other material as required.
This may reduce a significant amount of cost in material, and time for installation.
It will most likely still need some sort of waler and anchor system however but this may simplify things.
Please refer to the following links for more details:

http://www.giken.com/int/st/index.html

(note that the tubular sheet piles are not propriotary despite what some companies imply)
There also used to be details on the Nippon Steel webpage however I cannot find the link.

 

[VoyageofDiscovery]

Hi dougsmart

Have you considered scour and extreme low water level during storm surge?

I also think driving 21m in stiff clay should be tested first.

VOD

 

[VoyageofDiscovery]

How far back are the anchors?

 

[carmoch]

What type of wall or method I could use for retain 21 meters of filling? I think it´s impossible to use anchors or something.Is it possible prefabricated structural elements? Do you know any case?
Thank you

 

[Geotechnical76]

dougsmart,

Your case is not unique. It has been done in the past. I have extensive research in this regard. The following publication may help you (case history):

Bjerrum, L., Kenney, C., and Kjaernsli, B. (1965). “Measuring Instruments for Strutted Excavations,” Journal of the Soil Mechanics and Foundations Division, SM1, p 111-140.

Soil strength=400-800 psf
Dimensions of excavation: Length=38, Width=36, Depth=89
Number of strut levels: 3
Location: Gronland 2, Norway

Also there is another paper by [Hsing and Berman (1953)]. I think they had an excavation 19 meters deep in Chicago in medium stiff clay.

Good luck