# Considerations for pouring a rather tall concrete pier?



## acro (Jan 14, 2013)

I know my trade says electrical, but that is just one of the things I do. I really do it all around here.

So, in excavating for a footer for a rather large point load, I encountered a very large void. It is basically a large open pit about 12' deep and many square feet in size. We are pumping the water out now, so I have not seen the bottom, but my money is on a thick concrete slab.

Moving the location of my new footer is not really an option, so I need to address the issue of the void. The void is about 60% of the area of my proposed footer. I might post some pics later.

My plan is to install a galvanized culvert pipe vertically in the hole and pour if full of concrete. I plan on getting it in the hole and secured against movement and then drop a few bags of quick-crete down the hole to seal the bottom. After that sets up, I will order the concrete.

So, should I order anything other than what I would pour for a slab? What about the free fall? I don't see how I can limit the fall to less than 13' initially. Should I do it in lifts?

I am assuming the metal culvert can take the pressure, and i already have several of then on hand, but would I be better off with a plastic culvert? 

Total footer size if about 48x48 and the culvert is 22"

Thanks


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## rjconstructs (Apr 26, 2009)

There are a lot of factors to consider. This is a column with "a rather large point load", is one. Is there an engineer around that you can call on to give you some specs for sizes? The culvert pipe is a good idea but what size? (22? 24?) Are you going to lay steel in it? What strength concrete are you thinking? I don't like the idea of dropping the concrete 13' but if you vibrate it as you go up you can lessen the separation that might occur. Keep us posted on what you figure out.


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## 11678 (Jan 11, 2007)

A large void = future sinkhole ?


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## FramingPro (Jan 31, 2010)

Concrete placement rate and consolidation .And finally bracing!!! You will find out that you have too little bracing *much* faster then you will if you have too much.


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## acro (Jan 14, 2013)

11678 said:


> A large void = future sinkhole ?


I can see where my description might imply that.:laughing:

Here are a couple of pics.











The original floor was built up about 27" due to flooding, and this service pit was never filled in, just covered over. I suppose got lucky(or unlucky :lol when I laid out the cuts for the slab, two of them pretty much lined up with the old access hatch.











I have a little prep work to do.


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## acro (Jan 14, 2013)

Is there an engineer around that you can call on to give you some specs for sizes?
I am not familiar with any, but I am in southern Ohio if you know of any.


The culvert pipe is a good idea but what size? (22? 24?)
About 22"


Are you going to lay steel in it?
Was not planning on it.



What strength concrete are you thinking?
5k psi, but that was one of my initial questions.



I don't like the idea of dropping the concrete 13' but if you vibrate it as you go up you can lessen the separation that might occur.
What about adding any friction modifiers or other additives to the mix? The drop would be straight down, so nothing to hit that could separate the mix and cause graveling. That's my thought anyway.


This building is an old service facility for DT&I trains.


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## acro (Jan 14, 2013)

Maybe the point load won't be that great. :blink:











That is just an area of about 50'x70'. Ceiling height is about 30'

I've got more pics of that truss, but they would just cause more concern.


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## griz (Nov 26, 2009)

If that culvert is going to bear a significant point load it will likely be driven into the ground. 

If your goal is to fill the hole & provide a bearing point, why not fill it with CDF and leave the top 6-12" for concrete.

You don't "drop" concrete that far. A pump is used with a snout to place it. You can also push out any water this way.

It would be advisable to consult an Engineer on this.


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## acro (Jan 14, 2013)

I am not familiar with the costs of CDF. I am waiting for the ventilation to run a while before entering the space, but I figure it is at least 80 yards.

I do certainly prefer the option of filling the hole completely, but want to minimize the $$.


When you say you don't drop concrete that far, I have read otherwise. If the forms can hold the pressure.. and a round culvert will be very strong.

What do you think of this?


> That "hard splash" you invisioned is actually good as it helps consolidate the concrete in the lower levels. Thats why you don,t need to vibrate concrete that drops more than 20'.


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## griz (Nov 26, 2009)

CDF- Controlled Density Fill. 

Basically slurry. Cheaper than concrete & you can dump it right out of the truck into the hole. Also very quick.

Not permitted to drop concrete like that out here.


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## acro (Jan 14, 2013)

Thanks for mentioning the CDF. I will see if that might be an option around here.


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## Mellissam (Oct 27, 2009)

To take it one step further...if bottom of hole is sound (i.e. good bearing) fill it with a mix (3/8 minus - aka fill) and compact as you fill. Then two feet from top, make your footing with 5/8" rebar and use good concrete 30mpa = 4k psi or better. You'll have a solid footing, and a large one at that. Of course, swing it by an engineer, but it'll likely be your cheapest and less of a headache option...

BTW - A culvert will not blow out when filled with concrete...the max I've gone with sono-tubes (wax cardboard) is 8'...no higher due to drop, not ability of tube to hold it. Just bracing of top and bottom so it stays vertical, and minor uplift force when placing concrete. And I always use rebar so it complicates placement from a height. Almost pointless to use a culvert without rebar, unless an engineer says it can handle the shear requirements. Everything here revolves around seismic considerations.


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## chew (Apr 5, 2012)

The pier will need vertical reinforcement & horizontal ties. No drop more than 5ft. permitted. Use a snout on a pump or a bucket. Call local redi-mix co. they can recommend an engineer. Make sure you protect against vertical lift. I launched an 18" dia. x 14ft form like a missile once.


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## dayexco (Mar 4, 2006)

pump, clean out the debris, use an elephant trunk or a pump...fill it full of k-crete


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## Mellissam (Oct 27, 2009)

chew said:


> The pier will need vertical reinforcement & horizontal ties. No drop more than 5ft. permitted. Use a snout on a pump or a bucket. Call local redi-mix co. they can recommend an engineer. Make sure you protect against vertical lift. I launched an 18" dia. x 14ft form like a missile once.


I would have liked to have seen that...lol
That is quite the column...did the bottom blow out? What type of form? Good to know...

I try to use stiff concrete for columns (tell truck beforehand), filling 1/3, then comeback after a bit 15-30min and ease the rest in there...

Noticed on Sonotube site they say can fill a 20' in one lift...wow. I get nervous at 8'...the bottom when tapped feels like it wants to explode. Just an 1/8" of cardboard between me and disaster...


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## ssconstruction (Apr 13, 2013)

not sure if im understanding right. but from what I do under stand is I think you should install a new construction helical in the ground were you put your peir grip-tite had one of best out there go to there site and check it out
http://griptite.com/ 
they are made to build on unstable ground


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## acro (Jan 14, 2013)

I have seen the helical piers, and they do seem like a nice option in certain cases. However, we moved forward with the 22" culvert. I have not yet raised the roof and set the post, but preparations are being made.

There are definitely some unknowns regarding what is actually under there, but I am assuming that there is substantial concrete footing under the structure I placed the pier on. The pier is only supporting half of the footer. The other half is resting on the poured wall that forms part of the pit.


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## acro (Jan 14, 2013)

Well, there where no issues filling the culvert and then continuing on with the footing. Did them both in one pour.

Sorry, I didn't get any pics of it, but the concrete crew got it in the hole before I got there.



Finally got some of the fabrication done. Here is some of the progress I made today.

Here is the new post - 16" pipe.


This is fabricated from 6" WF beam. Grout is to assure good even contract with the bottom of the truss.






Just put some slight pressure on it until the grout sets.





Still mulling over how much I want to lift it before setting the "post".


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## MTN REMODEL LLC (Sep 3, 2010)

Cool job... great pic's..... creative thinking..... 

but looks like a commercial job.... why did customer not get some engineering stamps???... just curious


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## acro (Jan 14, 2013)

Thanks, We try to keep everything in house.


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## ubcguy89 (Mar 23, 2013)

acro said:


> Is there an engineer around that you can call on to give you some specs for sizes?
> I am not familiar with any, but I am in southern Ohio if you know of any.
> 
> 
> ...


here is the deal, you need to get an engineer!!! 
If you decide not to get an engineer, you need to get a pressure test done on the soil. If the soil is soft, you may need to drive piling, or possibly dig deeper for a caison.


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