Need more help with pole barn footings
I am stumped at what to do! As I stated in my other post, I hit water while digging footing holes for a polebarn. Digging down 4′ would end up with 2′ of water in the bottom of the hole pretty quickly. I put some stone in a couple holes and put 55 gallon drums in the holes and backfilled as a test. Well with yesterdays all day rain the water table must of come up, and the water pushed the barrels out of the ground. I know a barrel is pretty light and easy to float it since it still had the bottom on, but I am concerned about doing the footings right. How do I make a footing that will not be susceptible to being pushed out of the ground? I assume a concrete footing could be pushed up the same as the barrel. I am at a loss here, any help would be appreciated.
Dave
Replies
Didn't catch your earlier postings but concrete will not push out of the ground. If the bottom of your hole is firm (rock, gravel, firm soil, etc.) you can probably pour the concrete right into the hole (it will cure under water). Ideally, if you could cut the bottom out the barrels, shove them into the holes to act as a cofferdam (like the concept used in doing underwater bridge footings), pump the water out with a sump pump and immediately pour the concrete, you should be in good shape.
Some people would bitch even if they were hung with a new rope.
I can cut the bottom out of the barrels and make the cofferdams, so that will work out ok. How is it that the cured concrete footings will not push out of the ground? I know that hydraulic pressure can move a lot of weight and I am really concerned about this.
Dave
Concrete weighs more than water, 150# cu ft vs. about 62# cu ft. But you definitely need to be below the frost line. Joe H
JoeH,
thank you, no problem getting down below the frost line. I think the weight difference explains how I can pour concrete into the form even if there is water inside, as the cement will displace the water. Here is my concern, and what I am trying to understand. If the water table rises after the footings are set, the water will push in all directions and take the path of least resistance I assume. The soil I am digging in (if you can call it that!) is very dense clay and shale. How can I be sure that the water will find another path rather than push my footing up and out of the ground?
Dave
would increasing the size of the base of the footing as in a cone or bell structure add the desired mental assurance from the backfill acting as a pressure clamp instead of just trusting the weight of the concrete?
If I understand correctly, the scenario you're concerned about is water pressure from below the footing pushing it up like a piston through the top four feet of soil. Wouldn't that require a completely impermeable layer of clay to form the cylinder? It seems unlikely to me that the soil would be porous enough to allow groundwater to rise to the bottom of your footings and then all of a sudden seal up so tight the pressure doesn't have anywhere to go besides your footings.
But even if it does act that way, couldn't you put a layer of gravel under the concrete and backfill the holes with gravel or road base or something that can be compacted enough to resist lateral load but porous enough to relieve the water pressure?
You must Believe in the Force, my son. In this case it's the force of gravity, but any force will do. It just ain't gonna happen unless it freezes beneath your footing. The Dark Force is more powerful the the Regular Force when it's frozen. Joe H :)
You have got to believe these people and pour your concrete so you can get moved in to your new building.
Quit asking already and pour it.
Here is something to think about. If the water could push up a footing, wouldn't all the big ole rocks be squirting up out of the ground when the water table is up? I don't think so either. So I don't think that will happen with footings either. And you have a barn pushing them down anyway. So if I was to worry about something it would be the barn sinking below the earth, what with all the soft mud under the heavy footings with a barn up on top.
Next time you see a flood on the TV, see if you can spot anyone hanging onto their patio as they go by? Every see any cinderblocks floating down a river? Joe H
Now that was an excellent reply!! Thanks for the laugh! Some people would bitch even if they were hung with a new rope.
OK I think I get it now :) Yes I see how leaving the barrel bottom in was the mistake, I already cut the bottoms out of about a dozen to use. Now you are going to get me worried about the building sinking! I have very dense clay like soil where I am building so I hope there wont be any problem with the footings going down. I plan on putting 6" of crushed stone under the footing to help with drainage. Thanks guys and as soon as I get my backhoe repaired (blew a cylinder sunday) I will get back to work.
Dave
Having built pole buildings for over 20 years I can assure you that the footings are not coming out of the ground. These men have given you some good information. The main purpose of a footing in a pole building is primarily to keep the post from sinking. After that, to resist uplift. The post must be anchored in the concrete to achieve both. Either use a short piece of re-bar thru the post, extending out 2" on each side, or 5-6 nails partially driven in, etc. (Use the latter only if other means fail). I have encountered situations like yours. Be sure the bottom is free of lose dirt, drop in a bag (45#) of sackcrete, set the post, drop in another bag & backfill. Even if there is water in the hole, the concrete WILL set up, (see, I told you they were right!) Limestone is probably the best backfill material, but that hard clay is ok to.
P.S. After 500+ never had one float yet.
The only mistake was not cutting the bottom out of the barrel. I was amazed to read that you had left it on.
Just like cutting ther bottom out of your boat...believe me, it'll stay down - just like the Titanic does.
Dig a hole , drop in a Bigfoot (advertised in the FH magazine) , backfill , get it inspected, then pour the footing. The Bigfoot ad will ease your worries.
You're creating yourself a ton of extra unnecessary work with the barrels. Heck why don't you just sink piers to bedrock and remove all your worries?