RC Box Culvert Headwall-Footing Design

[JHart_11]

I need to design a headwall/foreslope wall & footing with a cutoff wall for a reinforced concrete box culvert using LRFD. Is there any design guidance available for this? The earth will be 6" deep at the back of the headwall and rise at a 2:1 slope. I plan to use dowel bars to connect the headwall to the precast box culvert. Any advice would be appreciated.

 

[TehMightyEngineer]

Oh, box culverts! My specialty!

For the headwall the biggest thing will be if guardrails will be attached to the headwall or not (hopefully not, what a nightmare when they are). Given your 2:1 slope down to the headwall I suspect this is just acting as a soil erosion stop. If so then your biggest load will be the loads during shipping (essentially nothing). Because they will have to be a secondary pour you will want to dowel them enough so they can't just be kicked off or broken off during 75 years of service; but otherwise be nice to the precaster and don't using a million dowels with the most expensive epoxy. I'd honestly leave the dowels, anchoring details, and headwall reinforcement as something the precast details and submits to you. This will allow them to submit materials and details they typically use and can do at low cost. Dowel bars epoxy anchored is the detail we use but I've also used/seen threaded couplings for this.

By foreslope wall & footing I'm not quite sure what you mean. Do you mean the toewall and/or wingwalls? If wingwalls that varies heavily on the site, type of wall, and so on. We've done both precast cantilever retaining walls and modular block MSE walls with geogrid for wingwalls. Both work well and really just depend on what the design engineer/owner specifies.

If you want, just leave it up to the precaster to design and detail and submit to you. This is what my roll is at the company I'm at.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[JHart_11]

Thank you for the very helpful response. I agree that my headwall, which we also refer to as a foreslope wall, will just be a soil erosion stop. It will be a separate pour after the culvert is placed. Since it really doesn't take any load, is it acceptable to just provide temperature and shrinkage reinforcing? My wingwalls, will be designed as retaining walls. This just leaves me with needing to design a footing for the end of the culvert to sit on. Previously, we had standards we could pull the reinforcing and size of footing from but now we have to design using LRFD. The previous standards prescribed a footing with a cutoff wall that extends vertically from the end of the footing at the end of the culvert. I am not sure what loads to use for the footing and cutoff wall. I am thinking self weight of culvert and headwall and weight of water from design frequency storm. Are there other loads I should consider? I wish I could just have the precaster design this, but I am required to have it in my plans. Thanks again for you help.

 

[TehMightyEngineer]

Since it really doesn't take any load, is it acceptable to just provide temperature and shrinkage reinforcing?

That's all I use, some #4 bars for T&S and to control cracking and a bunch of hooked bars at 12" o.c. alternating hooks epoxy anchored into the culvert top slab.

Are there other loads I should consider?

I'm having a bit of trouble picturing exactly what you're talking about but if it is the toewall you're describing then self-weight + water sounds reasonable.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com