AASHTO Temporary Nongravity Cantilevered Walls Embedded in Cohesive Soil

[WBell]

I have set up a Mathcad Prime worksheet (PDF copy attached) which solves for the required depth of embedment, D, for the lateral earth pressure shown in Figure 3.11.5.6-5, AASHTO 2010 LRFD Bridge Design Specifications. The retained soil and embedment soil are both cohesive. The worksheet solves for D = -6.15 feet for an excavation depth of 18 feet using the flange of an HP 14x117 member to engage the passive pressure resistance (b = 14 inches). The piles are spaced at 6 feet on center.
I am going to develop a model for the same conditions in PYWALL (Ensoft) to see what the response of the wall is. The AASHTO model only provides the required depth of embedment to maintain equilibrium and it is up to the user to evaluate strength criterion such as flexural/shear loads on the member and serviceability criteria (e.g., deflection).
I have also submitted the worksheet to the Mathcad developer to check on how to plot the equation for equilibrium of forces about the tip to see if there are other reasonable (i.e., greater embedment depth) solutions.
If anyone else has used the AASHTO equations for nongravity retaining walls as a check on software (PYWALL/LPILE), I would appreciate your comments and observations.

 

[jdonville]

Don't mean to rain on your parade, but there are enough commercial purpose-built software tools that solve these kinds of problems (and integrate into larger suites sometimes) that I don't see why you are doing this other than for the intellectual exercise.

 

[PEinc]

How well will your MathCAD Prime file work when you have multiple soil layers above and/or below subgrade? What about a water table above or below subgrade? As jdonville said, "There are enough commercial purpose-built software tools that solve these kinds of problems." What you are trying to do is a very important exercise as background for using design programs, but it is hard to write a MathCAD program that will handle all of the possible soil layers and water table elevations. Download a demo program or buy a program, and then check its results using your hand calculations as verification.

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