E80 COOPER RAIL LOADS TO RETAINING WALL 1

[alumpkin]

Looking for commentary about the design of retaining wall (abutment wall) for rail loads from E80 Cooper engine when rails are perpendicular to the retaining wall …..not parallel.

Alan L. Lumpkin, MS, PE
Greenville, SC

 

[SlideRuleEra]

I've considered the E80 loading to be an 1880 lb/ft² surcharge that starts at the wall but only covers a length of wall equal to width of the ballast (say, 10' +).

Loading magnitude (1880 lb/ft²) from: AREMA's "Retaining Wall Design for the Railroad Infrastructure"

http://www.SlideRuleEra.net

 

[robyengIT]

in addition to what said by SRE (drawn from "Concrete Pipe design manual" - American Concrete Pipe Association)

 

[alumpkin]

Thanks for all responses.

Alan L. Lumpkin, MS, PE
Greenville, SC

 

[alumpkin]

OK guys.....I get the 1880 psf load as surcharge load and I also agree with that number. Now moving towards design, the load cases as defined by AREMA are as follows:
1.4(DL+5/3(LL+I)+E) …...there ia no impact on soils loads per AREMA CHAPTER 8 so that leaves the equation as 1.4DL + 1.4*5/3*(LL)+1.4E. Continuing...1.4DL + 2.34LL +1.4E. So, here's the question. That puts the soil load at 1880 psf * 2.34 = 4399 psf surcharge. If I assume an at rest pressure coefficient of 0.5 then the pressure behind the wall is 2200 psf.

Let me know what you think as these loads are then used to design the abutment/retaining wall.



Alan L. Lumpkin, MS, PE
Greenville, SC

 

[SlideRuleEra]

Agree that the lateral pressure from the live load surcharge, using your assumption for K_o, is 2200 psf. That value is not soil load, it accounts for weight of the train. To design the abutment/retaining wall, lateral earth pressure and hydrostatic pressure from ground water (if any) need to be considered at the same time. IMHO, each of those loads would be treated as dead loads. Earthquake load (appropriate for project location) should be included also.

http://www.SlideRuleEra.net

 

[PEinc]

Make sure that you check if Ko is required for your particular structure or if Ka is allowed. For sheeting walls, I always use Ka. Also, AMTRAK, for instance, requires adding a 50% LL impact factor on top of the Cooper E80 even though AREMA may not require impact. Check if your particular railroad (or railroads for shared tracks) require impact.

http://www.PeirceEngineering.com

 

[r13]

The railroad abutment usually is quite bulky, I opine at rest pressure is more likely to develop into. Make sure the information provided by the geotechnical report is suitable for factored load design method, or LRFD, so no "doubling safety factors" will occur.

 

[alumpkin]

Guys,

Thanks for your input.

Alan L. Lumpkin, MS, PE
Greenville, SC

 

[alumpkin]

@SlideRuleEra,

Yes...the above loading is only from the train itself and you must include the soil load + hydrostatic.

Alan L. Lumpkin, MS, PE
Greenville, SC

 

[SlideRuleEra]

alumpkin - Very good, including all the forces is so important that I risked being rude to make a point of it. Hope it did not come across that way.
If this is the coal unloading pit you have mentioned previously, I agree with your approach using K_o.
Also, train speed is so slow across and unloader that impact loading is probably minimal.

http://www.SlideRuleEra.net

 

[r13]

Does anybody know how the rail track behaves when across two mediums with drastically different stiffness - from soil to rigid abutment? How this situation was handled?

 

[oldestguy]

I once had the job of evaluating a corrugated pipe with oval shape as a pedestrian passageway in the backfill to the abutment of the bridge over the highway for the RR. It had been damaged in handling and was installed even if significantly distorted. Locals feared it might collapse under the loads of the rail road traffic. I installed some nuts on the walls of the pipe to serve as the references for measurements of vertical and horizontal distortion of the pipe when train traffic went over the pipe (and the bridge). Measurements were with dial strain gauges accurate to 1/1000" attached to adjustable "rods" between these reference points. Had the opportunity to control just where the wheel loads of the locomotive might be as well as any loaded cars. The loaded cars carried iron ore with axle groups close together for short cars. Heavy stuff. The axle loads from the locomotive were significantly less than those of the ore cars as demonstrated by the deflections measured. After a few sessions where these static and moving loads were applied and resulting measurements were made, there was no measurable residual distortion of the corrugated metal pipe. Whether the ore car loads were comparable to the old standards for railroad bridge loads I do not know. Certainly the diesel engine axle loads were lighter than for the iron ore cars.

 

[SlideRuleEra]

Does anybody know how the rail track behaves when across two mediums with drastically different stiffness - from soil to rigid abutment? How this situation was handled?

It's not a big problem, but has to be addressed on a regular basis. The following photo is from the web, but shows one of our coal car unloaders (I recognize the setting)

This pit founded on rock, with vertical sides and is over 80 ft. deep, 75+ ft. below the water table. The (welded) rail is on typical RR ballast all the way up to the side of the pit. In coastal SC we have deep poor soil, so all of the track is slowly but continuously settling. As the ballast settles the welded rail cantilevers away from the (non-settling) pit and slopes down over a horizontal distance of, say, 6 or 8 ft. The drop in elevation is very easy to see after a year or two but does not cause problems. Every two to three years we bring in a RR contractor to raise the grade of all of the track on the generating station site. Special equipment moves along the track, lifting it (including attached cross ties), "crams" more ballast under the track, and reset the track to the higher grade.

I discussed my experiences with track loading at the end of this thread.
In a nutshell, oldestguy is right, for modern trains the junction of two heavily loaded railcars remains worse than the locomotive.

http://www.SlideRuleEra.net

 

[r13]

SRE,

Thanks for the excellent detail.