Prosheet Boussinesq loading 2

[MPorada]

I applied a strip load to my wall design in Prosheet using the Boussinesq loading option. Comparing the results with CWALSHT, I noticed that Prosheet produced an embedment 50% longer than CWALSHT results and a maximum moment more than 3 times that calculated by CWALSHT. I did some research and found out that Prosheet applies a factor of 2 to the Boussinesq pressure equation whereas CWALSHT does not. After some further reading I discovered that this factor of 2 is a point of discrepancy across different software and design approaches. Can someone shed some light on where this factor of 2 came from and what you use in your sheet pile designs? I have never used it before (since up to this point I have used CWALSHT or hand calculations to design sheet pile) and fear applying it may result in a very conservative design.

Thank you.

 

[Guest090822]

NPorada - Boussinesq's work was largely based on a rigid wall - with the following explanation:

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Steel sheeting is usually considered a flexible wall. Some DOTs and programs apply "Wall Factors" to the boussinesq pressure. The wall factors generally vary from 1.0 for a rigid wall, 1.5 for semi-rigid, and 2.0 for a flexible wall. I've been doing sheeting designs for over 20 years and have always used the 2.0 flexible wall factor in my designs if using boussinesq loadings. The boussinesq pressure would be divided by 2.0 in this case.

I've verified the Prosheet program and it does a pretty good job. It's based on the USS Sheet Pile manual.

You will find that there are a lot of inconsistencies with geotechnical engineering software. In the end it comes down to judgement and knowledge of what's going on.

 

[PEinc]

If you are designing for a DOT or agency, make sure you check to see if they have a particular Boussinesq equation that you must use. In my experience, railroads want the equation for a rigid wall (Eq. 12.33 in the above response).

http://www.PeirceEngineering.com

 

[Guest090822]

I've used the Cooper E80 loading with the flexible wall factor of 2.0 in the Northeast - never even had a Railroad company question it.

 

[MPorada]

Thank you for the explanation. I greatly appreciate it!

 

[PEinc]

Rick, that is very interesting but the reduction for a flexible wall does not comply with AREMA. Do you have a reference for allowing the reduction? Which railroads have let you use a 50% reduction (2.0 factor) to the E-80 surcharge? Attached is the Boussinesq equation used by several well-known railroads and AREMA. I am also in the northeast.

EDIT: I forgot to add Amtrak which also requires an additional 50% load for impact.

www.PeirceEngineering.com

 

[Guest090822]

PEinc - I've only dealt with temporary sheeting walls, usually not in place for more than a few weeks. I've dealt with Canadian-Pacific, D&H, Metro North, CSX, Amtrak, and probably a few more I'm forgetting.

I've always did the designs, sent them off for review/approval, and nothing ever got rejected. The best part - surprise! The walls didn't fail!

It may be a different situation for a permanent wall. I'm sure the wall design would get more scrutiny. I also know that dealing with the railroad companies are worse that dealing with state DOTs. You are at the mercy of the reviewers, and most don't know their own standards.

 

[PEinc]

Rick, I agree with you. Most of my walls are temporary. I assume that you have not been commented on about the surcharge reduction because the reviewers are not looking closely and just check to see if you used Bussinesq. In my experience, the surcharge reduction for railroad jobs, temporary or permanent, is not allowed per individual railroad and AREMA specifications. I have specifically be told by Norfolk Southern that my Boussinesq surcharge pressure must at least match those pressures tabulated on their chart that I included in my previous response attachment. I have had to verify that my Boussinesq pressures matched the Norfolk Souithern chart. Maybe I should again try using a reduction for railroad work. I already do use a flexible wall reduction for non-railroad projects.

http://www.PeirceEngineering.com

 

[MPorada]

TheRick109, so just so I’m understanding this correctly, if I have a strip load of 900psf over 3ft. I would enter q as 900psf knowing that the program will apply a factor of 2 to the pressure? Or are you saying I enter q/2 (450psf)?

 

[Guest090822]

MPorada - You would still enter the 900 pdf and the program will apply the appropriate wall factor. I will stress that this is only for the boussinesq pressures. Anyone that knows this topic knows that the work was based on rigid walls and it is often clearly stated in textbooks, commentary in the codes, etc. that his work overestimates surcharge loadings on flexible wall systems such as steel sheeting or solider pile and lagging systems. I have based the majority of my work off the the New York State Department of Transportation's Flexible Wall Design Manual, or GDP-11 if you want to download a copy.

PEinc - I have heard of Norfolk Southern, but I don't recall ever doing work for them. It's a simple fix if they were to make me change the wall to a rigid wall, it may require a different sheeting size or pile, but end the end they just end up paying more for being stubborn and unreasonable.

 

[PEinc]

Ha! Money (other people's) is no object to the RR.

http://www.PeirceEngineering.com