Drilled Pier surcharging a culvert/pipe

[TWC3]

The contractors found a 12" culvert about 5' under where the drilled pier is to go. The vertical loading is only 500 lbs but with the weight on the concrete itself, the load will be around 4 kips vertical. The drilled pier is 2ft in diameter and embeded 5'. Moving the drilled pier is not an option. I can however, reduce the embedment by making the pier wider but I still have the issues with the surcharge. Is surcharge even an issue with these type of loading on an existing culvert that should have been designed for all of the soil weight above it and traffic loads?

Thanks

 

[phamENG]

Coulda shoulda woulda. Best not to assume it was designed for traffic loading if you can avoid it - unless it was previously under a road and didn't collapse. Then I could see it. How far down is the culvert? Is it still active? What material - Brick? Concrete? How big is it? What kind of shape is it in?

What is your post supporting?

Is it that the foundation can't more, or what it's supporting can't move? You could always do two piers, one on either side, and bridge between them to support the super structure.

 

[STrctPono]

You could always do two piers, one on either side, and bridge between them to support the super structure

I would definitely consider this option.

 

[SlideRuleEra]

Cut a hole in the top of the culvert and pressure grout it full.

http://www.SlideRuleEra.net

 

[TWC3]

The drilled pier is supporting a pole structure that can not move. The 12" culvert is 5' below grade and appears to be made up of corrugated steel. I have no idea if it is active or not. Please see below for a picture.

 

[phamENG]

I'd try to find out more about it. If it's still active, then you probably want a geotech to weigh in and give you some recommendations. Though I think just digging deeper on the right side and letting the concrete pour down to a level closer to the bottom of the pipe would probably do the trick - as long as you're not expecting much lateral movement out of it.

If it's not active, then either do that regardless of lateral movement, or follow SRE's advice and grout it.

 

[RPMG]

A section of it can be encased in concrete, or two footings can be installed with a bridge beam/pier above. Sleeves, insulation, or even CMU can be used around the culvert. Anything works really, but it requires a bigger hole.

It would not be appropriate for the new structure to rely on the existing culvert for strength, such as in soil bearing where it is surcharged. The culvert has a life expectancy, and it gets replaced at the end of it.

 

[BridgeSmith]

This is out of my area of expertise, but couldn't you just secure something compressible/collapsible just over the pipe, so that the pier bears on the surrounding soil and not the pipe?

Also, the pressure increase on the pipe is the 500lbs/end area + the difference between the unit weight of the concrete and the soil it's replacing (so, about 30pcf).

Rod Smith, P.E., The artist formerly known as HotRod10

 

[BridgeSmith]

There's also the option to dig the pier deeper to encompass the pipe. Unless the 500lb load added after the concrete hardens will result in significant settlement, the stress on that section of pipe becomes zero.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[LittleInch]

Well I would call it a drain or sewer and not a culvert, but it's a pipe of some sort. Those corrugated spiral ones tend to be quite thin so make sure no one stands on it, or puts any sort of point load on it.

If I was you I would lay a relatively thin slab to cover it - say 300mm over the top and let the slab go off, then just build away.

The issue is more likely to result in damage if you end up with 5 feet of liquid concrete bearing down on it.

Avoid any point loads and generally pipes can handle a lot of pressure if you don't subject them to liquid loading.

BTw what's a "drilled pier exactly??" any drawings of the foundation?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TWC3]

Hello LittleInch, what is the difference between vertical bearing pressure for liquid concrete vs solid concrete. I understand liquid concrete would affect the lateral pressure but vertical pressure should be the same if my understanding is correct. As for my approach, I plan on adding 9" of compacted soil above the corrugated pipe and just pour concrete over it. I effectively reduced embedment but increased the width of my foundation. Considering that the additional load is only 500 lbs vertical, surcharge should not be an issue on this structure especially if my foundation is now going to be 2.5'x2.5'. In addition, this corrugated pipe should be rated for traffic load since it goes under a road and a parking lot. The equipment and the bollards around it, if anything should shield the corrugated pipe from any traffic load that could surcharge it more.

 

[phamENG]

TWC3 - when the concrete is wet, it is a fluid load and has no internal stiffness. Once it sets up, the load follows the most rigid path. So if you fill the hole up with wet concrete, the pipe can collapse and the concrete will just follow it and crush it all the way. Solid concrete, on the other hand, will start to crush it but 1) the encasing concrete will limit distortion and stiffen the pipe (concrete has to crush for the pipe to flatten) and 2) as the pipe "starts" to crush its stiffness will drop and the relative stiffness of the soil supporting the solid concrete next to it will increase as a result. Load goes to the relatively stiffer support. End result - pipe isn't significantly deformed.

 

[r13]

The pipe does not looks like belong to any utility company, nor the city, but I probably would double check with them anyway. Is there any resident or facility around that potentially relying on it for drainage, it wouldn't hurt to talk to the nearby residents, and or business.

 

[r13]

Another way is a little fancy - arch over the pipe. For small load, this might just work.

 

[jdonville]

This is a classic changed condition discovered in the field. Unless you are the SER, kick the can up the chain and ask the designer what they want to do about it. If you are the decider, then I like RPMG's response: dig a bigger hole, if required, to accommodate a redesigned foundation for the pole that doesn't negatively impact the existing utility - they were there first.