Culvert extension settlement analysis 2

[vollEngineer]

I have never performed culvert settlement analysis before. I will have (4-foot to 8-foot) box culverts and (36-inch to 54-inch) pipes (RCP and CMP). My predecessor assumed 75%-full culverts and wrote up recommendations to limit settlement to one inch. He/she also neglected wheel loads. It all seems easy enough, but that is what makes me nervous. I am asking for lessons learned, if anyone is willing to provide.

 

[lovethecold]

I am assuming this is a culvert under a road. I would think that in most cases there shouldn't be a problem. However, it all depends on the soil below the culvert and how much the site will be built up over original grade. If you have some soft soils, then this could be a problem. I would want soil borings before giving any settlement recommendations.

I am thinking that if there is a road already at the site, a culvert may actually unload the site (from the void in the culvert). From culverts that I have seen, the culvert would cause some settlement, but the majority would come from the backfill covering the culvert.

Hope this helps, others can provide better guidance.

- EIT Geotechnical Engineer. I am here hoping to help, and learn a little along the way.

 

[fattdad]

Duncan has a worksheet on the stress concentrations beneath various culvert shapes for both the bedrock and the embankment condition. Bear in mind there is shear support that can develop on the sidewalls and the "roof" load must be conveyed by the sidewalls, which in turn must be redistributed at the base. If the base slab is strong enough, there can be some redistribution of stress. I'm just not sure I can get this scanned tomorrow and I'm travelling early next week. Otherwise, I wouldn't mind giving you a link to what I'm talking about.

On the topic of lessons learned: Don't forget internal drainage. Consider enveloping the lower 1/3rd of the culvert structure with a bedding layer of gravel and the sidewalls also! That way, seepage forces acting along the interface of the culvert concrete and the bearing soil/culvert backfill will be protected from piping failure.

Hope some of this helps. Some of this is common sense, other then the structural design of the sidewalls and base slab.

f-d

¡papá gordo ain’t no madre flaca!

 

[vollEngineer]

Thanks so much, y'all. I did get some borings and will certainly be looking at the results of the fill placement.

I will be looking into the cradle option today (I don't know yet if the original culverts were installed on cradles or not and how the difference would be good or bad.)

There's a FEMA Technical Manual about "conduits" through emabnkment dams that had some interesting points about over-compaction around structures and erosion in case anyone else is interested.

http://www.fema.gov/library/viewRecord.do?id=1827

I think I'm comfortable with my approach, now. Thanks so much for responding. Of course, feel free to continue to pass anything along. Report isn't due until Friday