Pier block or alternative uneven ground?

[Zeth]

So my ground is lava covered in about a foot of soil. Site is on top of mound. I'm going to start on the 12 x 18 soon. Not sure how to build the piers considering ground is uneven. Thought about sonotube and just pouring but sonotube is extremely expensive on the big island. Buying wood for forms seems just as big of a waste. Any suggestions? I though about just a lot of manual labor breaking up the lave and filling with concrete and Simpson tie then leveling the 4x4 post. Thanks for ideas.

[MountainDon]

lava covered in about a foot of soil

Not sure what that really is.  Our place sits on about 10-12 inches of more or less dirt on top of several hundred feet of pumice that is of variable size, nearly dust to small apple size, well packed and firm. That was blown out of the volcano and fell as debris. Or is your lava more like that from a hot lava flow that is like a rock layer?

[John Raabe]

For a utility building you might consider the concrete block pier shown here. http://countryplans.com/foundation/index.html

Take a look around the neighborhood at what has been done (and what has lasted). Also check if you are under code requirements. You might want to find out the bearing capacity of the lava. I see lots of pier and beam when I've been on the big island, but don't know if things are different on more recent lava flows.

[rick91351]

First off 

You might want to move this thread to General Forum.  That gets a lot more traffic.... (Done - Moderator)

I can see several issues using sonotubes or piers from lumber and only a foot to the bed rock.  One problem I see is securing either well enough to keep them from floating up when you fill them.  There are a few ways to prevent that and be aware that can happen.

Sonotubes some places for some reason are out of sight expensive.  A couple places in Alaska and Canada are so the big island I would also be suspect.  So rather than buy boards - though in most cases you can really find uses for them latter.  You might start looking around for other stuff you might use for free.  Discarded wooden shipping crates or discarded pipe or culvert.  Hawaii might be a great place to try a rubble stone foundation if legal.  Sort of think out side the box you might say!   

[Redoverfarm]

Not sure of the availability of materials but if they are available you might consider Flue blocks laid on a concrete footing. Even standard 12" corner or line blocks could be substituted.   8-10" of concrete footing then stack the flue blocks which will act as form, filling them with concrete, rebar and fastner on top.  I am sure you probably have no frost issues so the depth is not a concern as long as you can hit something solid enough with your footings to rest on.  The amount of concrete is minimal in comparison to sonotubes and you can work on one at a time using bagged premix verses bulk copncrete from a plant whereas you normally pour all at the same time.  I might be wrong but I have heard that termites are a problem in that area and the blocks might give you some protection from them.

Here is 12" AND 8" Blocks used in different configurations to meet the design. The piers can either be faced later or even parged to give a somewhat finished appearance.

[Don_P]

Do remember that the big island is in the highest and second highest seismic design category depending on where you are. I'd be looking to local resources for what works under those conditions. From a paper I recall that rigid well braced posts that could slip on footing pads worked as long as they couldn't leave or topple the pad. Less well braced posts simply hinged over and collapsed under the structures.

[rick91351]

I would most likely drill and rebar the bedrock.  I would secure them with epoxy or molten sulfur.   BTW Mouna Kea  on the Big Island does get frost and snow.

Don_P's reference to the seismic area was one of the first things that came to mind.  One reason I brought up the rubble stone foundation.  I am sort of wondering if a rubble stone foundation would not be a good alternative here?  Or pin everything to the bed rock and let'er rock and roll and shimmy and shake?  Would the rubble stone use up energy and not transfer it so readily to the structure?

Where as I have never really read all that much on the subject I find it very interesting...

[JRR]

I'm certainly no expert, but I wonder how a massive steel reinforced slab ... sitting atop some well-drained loose stuff ... would fare?  The slab should be smooth-bottomed to prevent any "keying" to the earth.  The wall/footings could be attached to the slab steel.

[UK4X4]

"but I wonder how a massive steel reinforced slab ... sitting atop some well-drained loose stuff ... would fare?  The slab should be smooth-bottomed to prevent any "keying" to the earth"

I would imagine on a flat area OK accept for where the srvices come in...

However on the side of a volcano I imagine the ride down hill would be pretty outstanding.....till it stopped !

My foundation is a sort of floating bath tub over 4ft of crushed rock for drainage
it too is designed to sort of float in one piece even if things move.......we all joke about it ending up on the plot below if everthing shifts !

[Patrick]

A cheap way to do tubes is using 5 gallon buckets or regular tubes cut in 1/2 or 1/3  depending on the height you want if the soil can be dug without collapsing on itself cut the bottom out of the bucket and screw boards on both sides of the bucket supporting and leveling the bucket on top of the hole do the same thing with the tubes the boards will rip off after the concrete has set works well and saves $ sometimes the tubes want to lift a little when pouring so be proactive for that if you use this method!