Cantilevered Sheet Pile Design
Cantilevered Sheet Pile Design
(OP)
Hello Group,
I'm new to the forum, but have used advice from you guys for various projects in the past. Thanks for all your insight.
I have been tasked with designing a sheet pile wall for a 20-foot excavation (temporary, as it will be backfilled). The soil behind the sheet pile wall is organics/peat. Below 20 feet is a low-end medium dense sand. Static ground water is at about ground surface.
Are there any immediate concerns you have about this? Based on the organics behind the wall I don't see anchors as an option, so it will have to be entirely cantilevered. Do you see any concern with a cantilevered wall for a 20-foot excavation with ground water at ground surface on the back side and 22 feet +/- deep on the front side? I've read somewhere that cantilevered walls shouldn't be used for deeper than 15-foot excavations. Is this true?
Also, what do you think is the best way for me to design this wall? Should I design it all by hand calcs, or purchase software and do it both ways? Any recommendations for software I should purchase?
Thanks for all your help.
Brian
I'm new to the forum, but have used advice from you guys for various projects in the past. Thanks for all your insight.
I have been tasked with designing a sheet pile wall for a 20-foot excavation (temporary, as it will be backfilled). The soil behind the sheet pile wall is organics/peat. Below 20 feet is a low-end medium dense sand. Static ground water is at about ground surface.
Are there any immediate concerns you have about this? Based on the organics behind the wall I don't see anchors as an option, so it will have to be entirely cantilevered. Do you see any concern with a cantilevered wall for a 20-foot excavation with ground water at ground surface on the back side and 22 feet +/- deep on the front side? I've read somewhere that cantilevered walls shouldn't be used for deeper than 15-foot excavations. Is this true?
Also, what do you think is the best way for me to design this wall? Should I design it all by hand calcs, or purchase software and do it both ways? Any recommendations for software I should purchase?
Thanks for all your help.
Brian





RE: Cantilevered Sheet Pile Design
RE: Cantilevered Sheet Pile Design
Your wall probably could be tiedback with steeper tiebacks bonded into the sand below the peat. The problem would be cutting holes in the sheet piling below the water table. Can you internally brace the sheeting with either wales and cross braces or with wales and raker braces? I assume that the sheeting is a closed structure that forms a cofferdam. Otherwise, how will you control the water in front of the wall?
www.PeirceEngineering.com
RE: Cantilevered Sheet Pile Design
Some additional information: I just completed a round of test borings. Soil conditions (at their worst) are about 18.5 feet of ORGANIC SILT/ORGANIC FIBERS (i.e., peat with 50/50 fine fibers and organic silt), underlain by loose (Nave ~7) fine sand to 35 feet, elastic silt to 40 feet, and gravelly sand (glacial till) to 49 feet over bedrock. We completed 6 borings with a very consistent soil profile, spaced at about 150 apart along the proposed sheeting line.
So, my task is to excavate the peat, and I'm confined to the excavation so I can't slope. Previous geotech engineer's recommendation was to sheet and excavate, so the owner is stuck on this idea that we need to excavate the peat (rather than stabilize the peat via CMCs and grid-reinforced soil mat).
Here is the major issue: excessive depth of excavation for cantilevered sheet piling, peat has poor strength and groundwater is at ground level, so I have poor soil strength and hydrostatic pressure, soils at the toe are essentially loose saturated sand that has minimal passive support. Can't tie back because the soil behind the excavation is peat, and can't install cross-beams because the excavation width is 200+ feet.
So, in the end it appears to me that this is not a doable situation with sheet piling. The only reasonable solution is to rock socket H-piles, which is going to be extremely costly.
Does this seem like a doable situation, or do I just bite the bullet and tell the client this is just not possible with this method/within any reasonable cost?
I'm also brainstorming some kind of happy medium where we could sheet pile a less wide area, cross-support, and grid-reinforce outside the sheet piling (less critical area).
FUN PROJECT! But some hurdles.
RE: Cantilevered Sheet Pile Design
www.PeirceEngineering.com
RE: Cantilevered Sheet Pile Design
Drilling into bedrock below the water table in loose sand would be expensive. The holes would need to be cased and you would still need to use steel sheet piling that interlocks with the drilled-in king piles.
www.PeirceEngineering.com
RE: Cantilevered Sheet Pile Design
Mike Lambert