Concrete piers and saturated soil

[IHDiesel73L]

I've been kicking around ideas here for a while for a backyard shed I'm planning (it will be good training for a cabin one day) and I had originally intended on building a pole barn.  The problem is the building site.  The ideal spot for the shed is going to be the back corner of my yard-which looks like this:





This is a picture of an exploratory hole I dug to see what the soil looked like 4' down:



The hole began to fill with water as I was digging, so ended up using a wet vac to suck the muck out of the bottom so that I could see the profile of the soil.  It seemed to be uniform to the bottom.  A soil report for my area indicates that it is a "gravelly loam."  Its a brown/orange, gritty but sticky mixture, so I'm guessing the clay content is on the higher end for loam.  There is also a fair amount of broken rock, white/brown in color with flecks of gold (mica?).  It took about 15 minutes for the hole to fill completely to the top with water.  The soil around here is definitely saturated for sure with the snow melt (I live in Northwest NJ), but the speed at which the hole was filling surprised me.  That coupled with the fact that this spot has always been soft, and that the grass is green nearly year round has me wondering if there is a spring in the area.  I've ruled out broken water lines, old septics, etc...the town confirms that there are no lines in the area, we have public water and sewer, and before the subdivision was built in the late 1960s, the area was farmland.  I actually have a 1930s era aerial photo that shows open tilled land where my house stands now. 

Whether its poor drainage, or a spring, I need to figure out what, if any, kind of foundation will work for a 12' x 24' storage shed.  If I were to pour 12" diameter x 48" piers in that kind of soil would they simply sink?  Would it be better to spread stone over the entire area and place the shed on top of the stone, spreading the weight over a larger area?  I've been trying to think of way to drain the soil, but my options are very limited.  I am surrounded by neighbors on all sides so I can't just drain it off somewhere.  A drywell probably won't work because this layer of saturated soil could be 50' deep for all I know.  Is there anything I can do or is this land just not going to support a foundation. 

[rick91351]

It almost / it reminds me of a broken water main.

[Redoverfarm]

You might consider using the "big foot foundation".  It would spread the support in a bigger footprint. 

http://www.bigfootsystems.com/

[cbc58]

i've seen something posted here awhile ago which was an alternative pier system using a composite block with long metal pins that you drive into the ground at angles.  forget what it's called but if it's just a shed you might check that out to see if it could work if you exhaust other possibilities...

that looks like a good place for a garden...

edit: here they are: http://www.pinfoundations.com/

[rick91351]

Rather than the pier and post how about a regular foundation.  Footing or footer and stem walls....

[IHDiesel73L]

http://www.pinfoundations.com/

WOW...  Neat product.  Will definitely keep this in mind when we begin planning our cabin.  Not having to haul tons of concrete to an off grid building site in the Maine woods would make them worth every penny.  For a backyard shed they're a bit pricey at $130 a pop though. 

Rather than the pier and post how about a regular foundation.  Footing or footer and stem walls....

Again, seems like a lot for just a shed, but then again, its looking like if I want to build something that's not going to sink it's going to cost me...

[firefox]

Be sure to check with the local building department, zoning, etc. to see if they allow
that size of a shed and where on the property. There may not be a problem, but
it's better to ask in front. Some areas get really bent out of shape and make you tear it
down along with fines, etc. Spoken from bitter experience.

[IHDiesel73L]

Be sure to check with the local building department, zoning, etc. to see if they allow
that size of a shed and where on the property. There may not be a problem, but
it's better to ask in front. Some areas get really bent out of shape and make you tear it
down along with fines, etc. Spoken from bitter experience.

That part is all worked out.  I spoke with the zoning official about the permitting process and verified that I can put up a building up to 500 SF, up to 21' high, etc...anywhere I want in the yard as long as it's 10' off the property line.  Once I figure out where exactly I'm going to put it, I just need to give him a sketch on the plot plan with the dimensions, pay my $40, and I'm good to go.  The problem now is just the foundation.

[North Sask]

I'd wait until things dry up a bit and dig another test hole. The time of year (spring melt) might be throwing off the results of your experiment. Without knowing the lay of the land, it is difficult to say if a spring might be the cause of your problem. I'd put a small wager against it. I would be more inclined to say it's an area with poor drainage. This is all wild speculation, not being at all familiar with your exact location.

Loam generally refers to a soil composed of a mix of sand and silt with some clay (i.e., none of the three components dominate). Loam soil is good for growing things, so it makes sense that your yard would have historically been used as farmland. Gravelly loam would indicate that there is a greater amount of sand and gravel but still some silt and clay. A passing thought: This sounds like a soil that may be prone to frost heave (lots has been written about frost heave on this forum - give the search function a workout).

Are you planning to build a basic back yard shed for cold storage, or do you plan to turn this into an elaborate man cave with a finished interior? Will there be buried utilities connected to the structure? If it's just a storage shed, strip off the grass and topsoil, put down a layer of geotextile fabric (don't get sucked into the woven vs non-woven debate - it just won't matter much for this application), spread and compact a layer gravel/sand, and plop down your shed. Oh, I forgot the last step. Stand back and say "good enough."

[Don_P]

I wrote a post but didn't post it to avoid confusion between a shed and a dwelling. But, since Sask started it... . I'd build a crib of 6x6's well outside of the footprint, lag them together, maybe 2 rows high above grade. Drill and drive pipe in the ground to locate it firmly. Drape the geotex loosely and fill with clean washed rock to avoid capillary draw. Compact well in lifts.  Build and anchor well to the ground to avoid overturning in the wind, a 6x6 or at a min a 2x6 "sill". You still have a moisture problem inside, metal will rust and mold will grow. Use a 2x12 skirt to keep the siding above grade and to allow another layer of geotex, plastic, geotax, and more gravel. Now you're isolated from ground moisture and have a drainage plane inside. The sandwich keeps the plastic puncture free.

[IHDiesel73L]

I wrote a post but didn't post it to avoid confusion between a shed and a dwelling. But, since Sask started it... . I'd build a crib of 6x6's well outside of the footprint, lag them together, maybe 2 rows high above grade. Drill and drive pipe in the ground to locate it firmly. Drape the geotex loosely and fill with clean washed rock to avoid capillary draw. Compact well in lifts.  Build and anchor well to the ground to avoid overturning in the wind, a 6x6 or at a min a 2x6 "sill". You still have a moisture problem inside, metal will rust and mold will grow. Use a 2x12 skirt to keep the siding above grade and to allow another layer of geotex, plastic, geotax, and more gravel. Now you're isolated from ground moisture and have a drainage plane inside. The sandwich keeps the plastic puncture free.

Thanks!  I just want to be sure I'm understanding this correctly so I made a quick drawing of how I interpreted it:



As I understand it, stick framed walls would be constructed upon the 6x6 sills, which would form the perimeter of the shed inside the raised pad-is that correct?

[Don_P]

What you've drawn is what I was thinking for the foundation, basically the outer crib is containing the gravel "foundation". The sill could be a 2x6, although the 6x would certainly distribute the load better.  From there I was thinking of wrapping the sill with a treated 2x12 up on edge. Then using 6x6 posts for a post frame with horizontal girts rather than studs and vertical siding, board and batten or similar. The 2x12 skirt would be nailed to the posts and would keep the siding well above the gravel and splash zone. If you stic framed it I would want to use treated studs where in the post frame the posts would be treated but the girts could be untreated. If you wanted to go full tilt the 2x12 could be on top of the 2x6 sill and the 6x6 posts would be notched 1-1/2" deep  to accept the skirt, same notching for the girts. That would put the girts and posts in the same plane and build some rack resistance although I'd still work in some angled bracing unless the siding is a sheet good like T111.

[IHDiesel73L]

What you've drawn is what I was thinking for the foundation, basically the outer crib is containing the gravel "foundation". The sill could be a 2x6, although the 6x would certainly distribute the load better.  From there I was thinking of wrapping the sill with a treated 2x12 up on edge. Then using 6x6 posts for a post frame with horizontal girts rather than studs and vertical siding, board and batten or similar. The 2x12 skirt would be nailed to the posts and would keep the siding well above the gravel and splash zone.

Got it-it makes total sense to me now.  How would you anchor the sills?  I was thinking of drilling 1" holes at opposing 45° angles in the 6 x 6 sills and driving 1" x 48" rebar into the ground to create a kind of pin piling. 

If you stick framed it I would want to use treated studs where in the post frame the posts would be treated but the girts could be untreated. If you wanted to go full tilt the 2x12 could be on top of the 2x6 sill and the 6x6 posts would be notched 1-1/2" deep  to accept the skirt, same notching for the girts. That would put the girts and posts in the same plane and build some rack resistance although I'd still work in some angled bracing unless the siding is a sheet good like T111.

I'll definitely be stick framing and siding with T111 of some sort.  The roof will be purlins and steel.  Will post pics this summer-thanks again!

[akwoodchuck]

Now that looks like a perfect situation for screw piles if you ask me:  http://www.technometalpost.com.....I would do like DonP says and build the "sandbox", too though......  that way you won't have to work in the mud