Soil Surcharge at Abutment Case 2

[Marlow18]

I can't find an example anywhere depicting case 2. All of the tables in the manual show simplified calculations for case 1. I understand how to calculate case 1 entirely but I am having issues visualizing how to compute the lateral pressures due to case 2 in regards to surcharge only.

Would a small approach slab (3') affect the loading?

Any insight or reference would be extremely helpful.

Thank you in advance.

 

[PEinc]

Case 2 is just an area surcharge load of P = q x Ka. The lateral pressure diagram would be rectangular. You may need to read AREMA to see how it recommends applying a perpendicular E80 surcharge. The load would probably be applied to a length of wall that is greater than 9' (the tie length).

http://www.PeirceEngineering.com

 

[Marlow18]

I have gone through and read AREMA but would it only gives a paragraph. Would it still be the "q" calculation shown in the first part of the calc sheet? (the 80,000/(9x5) to get the rectangular distribution for a 1' strip?)

 

[PEinc]

Yes. q = 80,000# / (5' X 9'). If you can't find anything in AREMA about how wide to spread this perpendicular strip load surcharge, you may need to pick some reasonable width that is greater than 9 feet. Or, talk to the railroad's engineer.

http://www.PeirceEngineering.com

 

[Marlow18]

Ok I figured out how to distribute it through ballast over a different area. I know in AASHTO when you're applying surcharge, there's a certain depth where it stops having an effect laterally on a wall; would that be applicable to a scenario like this or do I have to extend the rectangular distribution an infinite length depending on my configuration?

 

[PEinc]

Many times over the past years, I have spread RR loading out over the ballast. For example, for 9' long ties with 3' of ballast below, maybe you will be allowed to spread the load over 9' + 3' + 3' = 15'. Also, the load could be applied at the bottom of the ballast rather than near the ground surface. However, sometimes this is not allowed. You really should check the specific requirements of the particular RR you are dealing with.

http://www.PeirceEngineering.com

 

[Marlow18]

Thanks PEinc. I was able to find a supplemental publication to AREMA that explained in perpendicular situations it spreads over the width of the tie and depending on your ballast like you suggested BUT only up to a max of 14ft; I don't think any further reduction is allowed beyond this point. The last thing I need to figure out is if I have an abutment sitting on a drilled shaft wall, how far down I would have to run this rectangular distribution of a load.

 

[PEinc]

If the drilled shafts are tangent to each other, they behave like a sheet pile wall and the surcharge would extent to the full depth of the shafts. If the shafts are spaced apart, you probably will be required to apply the surcharge to the full width and length of the shaft, at least to the top of bedrock, if any.

http://www.PeirceEngineering.com

 

[Marlow18]

I was hoping that wouldn't be the case but it seems like that's what it's going to end up being. Thanks for helping me out.