Anchored Sheetpile Wall - CWALSHT program

[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.

 

[PEinc]

I agree.

 

[DRC1]

The fixed earth computation assumes that the sheet is only driven far enough to devlop sufficent passive resistance to counter rotation about the anchor. Fixed earth figures that that if the pile is driven deeper, the pile will have significantly more stiffness to resist rotation. Thus free earth gives you shorter, lighter sheets but higher anchor forces. Fixed earth gives you lower anchor forces, but longer heavier piles. Geneally deflections are less with fixed earth. Either one is correct, just dont mix and match from the two. I would present both and let the engineer or the contractor decide which is more econmoical.