Anchored Sheetpile Wall Design (CWALSHT)

[BigEasyGeoSleuth]

I am using CWALSHT (Corps of Engr program) to perform the geotechnical design for an anchored sheetpile wall. The sheetpile has a retained height of about 22 feet, will be tipped in dense sand, and will have a single anchor at the top of the wall.

The program computes via two methods: 1) Free Earth Method, and 2) Fixed Earth Method. The difference between the two is the fixation at the tip of the sheetpile (free to rotate versus fixed). The results from the two methods are presented side by side in CWALSHT with differing values of penetration depth, maximum moment, etc.

My question is this: are both solutions equally valid? In other words, is it advisable to present the results (depth of embedment, maximum moment (& location), etc.) from both analyses in our geotechnical report. Then the structural engineer could have a choice of which section modulus and length of pile may be more cost effective for a given site. Or would it be better to go with one or the other?

My gut feeling is to pick the one with the bigger anchor force, which is the free earth method.

 

[kslee1000]

If list both results, it may causing fights in between the contractor, the structural engineer and the owner. I suggest to call the structural engineer in charge, explain and workout a desirable/suitable solution, then put that solution on your report. The reason is obvious, as a practicing engineer, I treat the engineering economy is an important issue, but only after given consideration of the subject the sheetpile wall is to protect. However, this view is not always shared by the contractor, or the owner.

 

[Gimbli]

I would go with the free eart method as my advisor in Grad School advisor (Frank C Townsend) said. We use free earth method because the same result your result shows, that is more conservative. There are designs in geotechnical engineering, like a sheet pile, that you must be very very careful.

 

[Touma59]

I have not used CWALSHT and am not aware if it does report pile deflections as well. I would also be curious to know if deflection is a consideration in this case. We do a fair amount of this kind of work near utility lines and exising structures, so in addition to the structural adequacy of the system, we must control deflections so we resort to the P-Y or 2-D Finite Element analysis. The reason I am bringing this up is because, a pile allowed to rotate at its tip (wether because the soil is weak or not enough embedment) tends to give larger deflections, and given that, as an order of magnitude, the vertical settlement behind the pile is closely related to its lateral deflection, this issue becomes important.

Tsoft;

http://www.tsoftonline.com