Anchored Sheet Pile using "Short Sheet Piles"

[mungchucks]

I'm currently designing a tieback system that will utilize a "short" sheet pile wall about 45' away from the main wall. The main wall is adjacent to a commuter railroad. The design criteria recommends to use the USS Steel Sheet Pile manual (which is similar to the more recent pilebuck manual). I'm trying to follow the methodology used in example 4 of the manual.

My tieback anchor is located 1.5' below the top of the sheet pile wall. Passive Pressure is 400psf/ft and active is 35psf/ft (F.S=1.0). For the design of the "short" sheet pile, I found that my point of zero moment occurs at a very shallow elevation (2.25' below top of wall). The anchor force that can mobilized at that depth is much smaller than what is required. Due to the constraints at the site, I cannot move the anchor location any lower than 1.5'. If I make my sheet pile wall deeper, I can mobilize enough passive to match the required anchor demand but end up with a moment at the base of the wall.

Is having a moment at the base of an anchor wall valid? The situation above is almost like a pile undergoing lateral movement since the anchor is relatively close to the top of the wall. Does anyone think doing a Lpile run treating the sheet pile wall as a pile worth it?



thread255-69993

 

[GeoPaveTraffic]

You are correct in assuming that it is not valid to have a moment at the bottom of the wall. If you do a LPile run, there will be no calculated moment at the bottom of the wall and you will have a much better handle on the actual loads in the short wall.

 

[PEinc]

Mungchucks,

Your description of the problem is very confusing. Why are you worrying about the point of zero shear? Why can't you develop enough anchor force with an anchor located 1.5 feet below the top of the sheet pile wall? Is the anchor angled downward? Are you concerned about the anchor pushing back the top of the sheet pile wall? How high are both sheet pile walls? Do you have difficult soils? In my experience, Lpile is not normally used to design sheet pile walls.

The US Steel Sheet Pile Design Manual IS the Pile Buck Design Manual. The Pile Buck Manual just has aditional information.

Other than that, I'm not sure just what your problem really is.

 

[DRC1]

If you look in the Pile Buck Manual (and posdsibly the US Steel manual) There is an explination of the equvilent beam. The conventional anaysis assumes the end of the sheet is pinned, and thus no moment. The equivent beam method assumes that if the sheet is driven deeper, it will be able to develop a moment below the dredge line. This method will result in lower anchor loads, less section modulus of the sheets and less deflection. It does however require longer sheets. If you are anchoring to a dead man, you can make the portion below the anchor deeper than the top to increase passive pressure.

 

[shockstressed]

agree with DRC1
that is what I would have said before reviewing the replies to date