Vehicle surcharge at top of Retaining Wall

[Builder604]

How do you calculate or where would you find a chart for how to apply vehicle loads to the top of a retaining wall.

 

[rochplayer]

For MSE walls, the typical live load surcharge due to vehicles is equated to a 2-ft layer of soil at 125 pcf or 250 psf all together per FHWA and AASHTO guidance.

 

[Builder604]

thanks for the reply rochplayer, This is a vertical cantilever retaining wall, would the 250psf still apply here. Large delivery trucks are the vehicles that will be backing up along the top of the retaining wall.

 

[cap4000]

250psf is typically used as the live load surcharge. If your wheel loads are very large and very close to the wall I would go to 300psf. How high is your wall??

 

[Builder604]

The wall is only retaining 6.1 feet at the highest point.

 

[Builder604]

Does anyone have any links to what surcharge is to be used. I have mainly seen 250psf. I have also read 600psf for large trucks. Also could a line load or point load be used to represent the wheel line closest to the wall?

 

[rochplayer]

I think the key is the application. The 250 psf is a uniform traffic surcharge that is used to represent traffic as it flows along the top of the wall and the superposition of thier wheel loads. In analysis, because it is a uniform surcharge, the surcharge times the appropriate K value is applied over the entire height of the wall.

My understanding is that it is not meant to represent a truck parked for long periods of time at the top of a wall. Such a truck would cause a high point load, but the load would be distributed with depth using a Bousineque (sp?) or 2:1 approximation. Therefore the top of the wall may experience localized higer stresses, but overall less than the 250 psf.

How close to the wall will the trucks travel? A conservative approach would be to determine the loading on the wall due to a parked design vehicle or the 250 psf loading, and design for the highest loads. My assumption, having not done any calculations, is that if you design for the moment and shear of the 250 psf surcharge load (plus the appropriate soil loading, of course), you likely will be designing for a higher bending moment than the static truck loads.

 

[MSEdesigns]

The AASHTO Bridge specs incorporate FHWA NHI-00-043 (Design and Construction of MSE Walls and Reinforced Soil Slopes) by reference. This file can be downloaded free from

http://www.fhwa.dot.gov/bridge/geopub.htm

We have done MSE walls for the ramps to primary crushers on quarries that support 200000 lbs vehicles. Bearing capacity has not been an issue due to the good rock substrate typical of a quarry. Main issue is to have what I call a well designed concrete spreading slab with a minimum thickness of 12 inches and well reinforced. This slab will make the load evenly distributed on a larger area making the load easy for the MSE wall. We have used Keystone blocks with polyester grids and A-1-a backfill.