High Water Table

[gdicks]

Ok, so after having provided some valuable feedback in another thread I have another dilemma. I am building a 18 x 24 shed / barn with a Pier and Beam foundation Piers will be poured concrete in sonotubes.

As Ive dug for the pier holes I am hitting standing water. Frost in my area is typically 4 feet so i need to get below that, however the standing water ranges from 3 to 4 feet down depending on the slope of the lot. My initial thinking is to raise the level of the lot such that I have 4 feet of ground above the water. Question is, how much above the water should I try to have my footing for the piers which will determine how much I need to raise the ground level, and how much larger than my 18 x 24 footprint should I raise the ground level?

 

[8N Ren]

What about steel driven piers? No digging required. My house build in 2010 we did that works really well.

 

[gdicks]

Dont know of anyone in my area who does this and the location on my property precludes access by equipment of any magnitude.

 

[6sunset6]

I have poured plenty of sonotube forms in water. Drill the hole with a post hole digger push down the sonotube. When ready to pour use a wet vac to suck out the water and mud at the bottom. I would not leave the tube in a wet hole for a long time. I pour the same day I put the tube in. Another note I have used a 12 inch auger and put 12 inch tubes in. 46 inches down. It s a little tight I have to wiggle the auger around for a while.

 

[gdicks]

I have poured plenty of sonotube forms in water. Drill the hole with a post hole digger push down the sonotube. When ready to pour use a wet vac to suck out the water and mud at the bottom. I would not leave the tube in a wet hole for a long time. I pour the same day I put the tube in. Another note I have used a 12 inch auger and put 12 inch tubes in. 46 inches down. It s a little tight I have to wiggle the auger around for a while.

What is the minimum size you would recommend for the sonotubes.

 

[Tractor Seabee]

This can be tricky depending on all the variables. If you can drill the hole w/o cave in you do not need the sonotube. What is at the bottom of the hole, mud, clay or well compacted material? despite the water table and the frost line you are not going deep enough for a friction to provide bearing so you need something firm at the bottom. You can place concrete in a hole full of water if you tremie or pump the concrete from the bottom up, it will displace the water w/o compromising your water/cement ratio. Raising the area has its own set of problems with compaction of the fill material to have the bearing capacity for what goes on the surface. This sounds technical, it is. Engineers get big bucks to figure this stuff out and prevent failure in the finished product. Lots of luck with your DIY engineering.

Ron

 

[6sunset6]

Size of tubes Depends on the load size of building, how many posts and snow load. You said 18 x 24 shed and you said frost at 48". You must be way north and so a lot of snow. A lot of posts are done by throwing a bag of mix in the hole and setting the post on that and filling the hole with dirt. I like to keep the posts out of the dirt completely. Lately I have seen pressure treated material fail in 3 years in contact with dirt. Out of the dirt seems ok. It is a little tricky doing 12 " tubes in 12" holes Because the post anchor hardware wants to be in the center of the concrete so the hole has to be in the right place. Tricky with a post hole digger. but it can be done. Need to stake the hole location local outboard of the hole and drill it plumb. Take your time. Enough about 12" tubes in 12 " holes. I would use 10" tubes for a shed. I have attached some pictures of 12 in 12 that I did for a lean to shed roof. I was going to use 10" tubes Building inspector made me use 12"

 

[skyhook]

Have you considered "Techno Post's'....

Just google it for more info.

 

[MacLawn]

Oh me boys, about the time I think we've got this pole barn posts figured out, me old haid starts spinnin' again. 1/2" I-Beam aluminum, that'd be the ticket I reckon! Techno Posts, eh? Ok, I'll research those thingamajigs too. Well OP (that'd be original poster for geezers like me), keep us posted...heheheheeee, that's a good one.

 

[BHD]

I would do some thing like the PERMI POST https://www.permacolumn.com/

Benefits of Perma Columns | Permanent Solution for Pole Building Posts

basically a concrete post bottom with some steel to attach it to the wood above ground, I think Morton buildings has gone to this type of construction, Foundation Options » Morton Buildings or offer it,